Water Resources Research Center University of Hawaii

2610 Pope Road Hbnolulu, Hawaii 96822

March 23, 1973

ERRATA SHEET

Please note the following corrections to our Technical Report No. 61 en­titled, A Rainfall Climatology of Hil03 Hawaii (by Charles M. Fullerton) and Technical Report No. 60 entitled, The Quality of Coastal Waters: First Annual FPogress Repopt (by L. Stephen Lau, Principal Investigator).

Technical Report No. 61

Page 1, Paragraph 3

Error: The Annual Summary of the "Hilo Local Climatological Data,11 published by the Environmental Data Service of the National Oceanic and Atmospheric Administration, contains a synopsis of the Hilo climate, as well as that of the published summary, together with additional data on the extremes of Hilo rainfall.

Correction: The Annual Summary of the "Hilo Local Climatological Data," publish­ed by the Environmental Data Service of the National Oceanic and Atmospheric Administration, contains a synopsis of the 11ilo climate, as well as that of the Island of Hawaii. The· following infOrmation is based largely on that pUblished summary, together with additional data on the extremes of Hilo rainfall.

Page 5, Lines 24 to 27

Error: amounts measures at the Hil0 airport. There appears to be no correlation between the frequency of frontal passages with the December~January monthly rainfall for Hilo during the 30-year period results in a curious inverse relationship (see Table 1).

Correction: amounts measures at the Hilo airport. There appears to be no corre­lation between the frequency of frontal passages and annual rainfall Comparing December-January frontal passages monthly rainfall for Hilo during the 30-year period results in a curious inverse rela­tionship (see Table 1).

Page 16, Figure 6

Shaded portion refers only to rainfall received during 50% of the years of record. Arrow should point at the dot in the center of the shaded area.

Page 18, Figure 7

Shaded portion refers only to rainfall received during 50% of the years of record.

Page 21, Figure 9

Time intervals 3-4: upper block should be shaded to indicate rainfall intensity of 0.50 - 0.99 IN/HR. Time intervals 13-14: the upper block is correctly shaded; the next block down, now unshaded, should be shaded to indicate rainfall intensity of 0.25 - 0.49 IN/HR.

Page 23, Figure 11

Time interval 2-3; the upper block is correctly shaded; the next block down should be shaded to indicate rainfall intensity of 0.25 - 0.49 IN/HR. Time interval 12-13: the upper block is correctly shaded, the next block down should be shaded to indicate rainfall intensity of 0.25 - 0.49 IN/HR.

Page 34, 7th Reference

Error: U.S. Department of Commerce, National Oceanic and Atmospheric Administra­tion, Environmental Data Service. 1970. Local climatological data, annual summary with comparative data, Hilo, Hawaii. 4 p. (In addition, weather parameters including hourly rainfall, as measured at the Hilo airport station.)

Correction: U.S. Department of Commerce, Na.tional Oceanic and Atmospheric Admin­istration, Environmental Data Service. 1970. Local climatological data3 annual summary with conrparative data, Hilo, Hawaii. 4 p. (In addition, Local Climatological Data is published monthly, re­porting a variety of weather parameters including hourly rainfall, as measured at the Hilo airport station.) - __ t_""'""=

Technical Report No. 60

Page 7, Line 1

Error: a) Undeveloped land areas, e.g., Waialua Bay, Oahu

Correction: a) Undeveloped land areas, e.g., Kahana Bay, Oahu

A RAINFALL CLIMATOLOGY OF HILO, HAWAII

by

Charles M. Fullerton

Technical Report No. 61

UHiVlET 72-03

December 1972

Partial Project Completion Report of

SPACE-TIME VARIATIONS IN HIGH INTENSITY RAINFALL ON THE WINDWARD COAST OF THE ISLAND OF HAWAII, PHASE I

OWRR PROJECT NO. B-024-HI, GRANT AGREEMENT NO. 14-31-0001-3575 Principal Investigator: Charles M. Fullerton

PROJECT PERIOD: July 1, 1971 to December 31, 1972

The programs and activities described herein were supported in part by funds provided by the United States Department of the Interior as au­thorized under the Water Resources Act of 1964, Public Law 88-379, and were performed with the cooperation of the Cloud Physics Observatory Department of Meteorology, University of Hawaii.

ABSTRACT

Annual~ monthly~ and houply rainfall data for Hilo~ Hawaii are plotted and analyzed as a preliminary phase of the study of spaae-time variations in high intensity rainfall in this loaality. A brief summary of the Hilo alimate is provided. Annual rainfall amounts are shown to be highly vari­able~ while the annual rainfall frequenay remains relatively aonstant at about 33 peraent. Monthly rainfall and maximum 24-houp rainfall amounts are displayed in the form of a monthly rainfall expectancy graph.

Houply rainfall amounts are divided into four intensity categories: O.Ol - 0.24~ 0.24 - 0.49~ 0.50 - 0.99 and ~ l.OO inches per clock hour. The percentage distribution of annual and monthly rainfall amounts and fre­quencies by rainfall intensity category are plotted and discussed. Hourly data are displayed in a series of monthly diurnal distributions by rainfall intensity category.

iii

CONTENTS

LIST OF FIGURES ............•..•.................•........•............... i v

LIST OF TABLES ....................................•...................... IV

I NTRODUCTI ON .............................................................. ,

CLIMATOLOGICAL SUMMARy ....•..........•.......•.•..•.....•..••....•...•.... 1

HILO ANNUAL RAINFALL ......•............•.•....•...........•..•....•..•.... 7

MONTHLY RAINFALL IN HILO ................................................. 14

HILO DIURNAL RAINFALL ..................•.....•.•...•......•.............. 17

OTHER SOURCES OF INFORMATION ...................•.............•........... 32

ACKNOWLEDGEMENTS ..•.......•..•...•............•................•....•.... 33

REFERENCES ............•...••..•......•........•.....••......•.........•.. 34

LIST OF FIGURES

1. Topographic r~ap of the Island of Hawaii .............................. 3

2. Annual Rainfall in Hil0 for 1931-1970 ..•..•......•................... 8

3. Percentage Variation in the Annual Rainfall in Hil0 in Four Intensity Categories (1953-1970) ..............•....•........... 10

4. Percentage Variation in Annual Rainfall Frequency in Hil0 in Four Intensity Categories and Trace Amounts .•.................•.. 13

5. Monthly Rainfall for Hil0 (1931-1970) ..•......•..•.................. 15

6. Quartile Distribution of Rainfall in Hil0 by Month (1931-"1970) ....•.....••......•.....................•.........•...... 16

7. Quartile Distribution of Maximum 24-hour Rainfall in Hi 10 by Month (1953-1970) ........................................... 18

8. Percentage Variation "In Monthly Rainfall Amounts in Hil0 by Four Intensity Categories (1953-1970) ....................... 19

9. Monthly Diurnal Rainfall Distr"ibution for Hil0 Showing Total Rainfall per Clock Hour by Intensity Category: January 1953-1971111 ..••.••••••••..•••.••.•.•..••.•........•••.••••... 20

10. Monthly Diurnal Rainfall Distribution for Hil0 Showing Total Rainfall per Clock Hour by Intensity Category: February 1953-1971 ...•..............•.....•.....•...•..........•.•.. 21

11. l\1onthly Diurnal Rainfall Distr"ibution for Hilo Showing Total Rainfall per Clock Hour by Intensity Category: \\1arch 1953-1971 ......•.••...•....................•...........••...•. 22

iv

12. Monthly Diurnal Rainfall Distribution for H"ilo Showing Total Rainfall per Clock Hour by Intensity Category: April 1953-1971 .••.•...•••••••.•••..•.•••••••..•..•.•.•••.••.•...•.. 23

13. Monthly Diurnal Rainfall Distribution for Hi10 Showing Total Rainfall per Clock Hour by Intensity Category: May 1953-1971 ........................................................ 24

14. Monthly Diurnal Rainfall Distribution for Hilo Showing Total Rainfall per Clock Hour by Intensity Category: June 1953-1971 ........................................................ 25

15. Monthly Diurnal Rainfall Distribution for Hil0 Showing Total Rainfall per Clock Hour by Intensity Category: Jul y 1953-1970 .......................................................... 26

16. Monthly Diurnal Rainfall Distribution for Hilo Showing Total Rainfall per Clock Hour by Intensity Category: August 1953-1970 •.•.••.•..•.•..••.............•.............•.•••.•. 27

17. Monthly Di urnal Rainfall Di str-j buti on for Hilo Showi ng Total Rainfall per Clock Hour by Intensity Category: September 1953-1970 .•..•......•...............•.....•.•......••••..• 28

18. Monthly Diurnal Rainfall Distribution for Hil0 Showing Total Rainfall per Clock Hour by Intensity Category: October 1953-1970 .....•.•..•......•..••.•••..••....•••.•...•..•...•. 29

19. Monthly Diurnal Rainfall Distribution for Hilo Showing Total Rainfall per Clock Hour by Intensity Category: November 1953-1970 .•..••..•.......•.••..•.•...•.•......•..••........ 30

20. Monthly Diurnal Rainfall Distribution for Hilo Showing Total Rainfall per Clock Hour by Intensity Category: December 1953-197 O ................................ III •••••••••••••••••• 31

LIST OF TABLES

1. Frontal Passages and Hilo Rainfall (December-January) .•.•.••.•.••... 6 2. Percentage Amounts and Frequencies by Rainfall Rate ..•••..••.•.••.•• 11 3. Rainfall Data by Intensity Categories ............................... 12

v

INTRODUCTION

As a preliminary phase of the study of space and time variations in

high intensity rainfall on the windward coast of the island of Hawaii, it

seems advisable to examine the general characteristics of rainfall in

Hilo. In particular, it is of interest to know the diurnal variation in

rainfall; that is, the total quantity of rain recorded during each hour in

the various months of the year. From these monthly diurnal values, it is

possible to construct seasonal or annual diurnal curves to study yearly

rainfall trends or to compare conditions during limited experimental

periods with historical variations over longer intervals of time (see, for

example, Takahashi and Fullerton, 1972). Furthermore, it appears appro­

priate to evaluate available rainfall records in the light of hourly varia­

tions in rainfall. This analysis can be viewed as a first approximation to

the study of instantaneous rainfall rates in Hilo and its vicinity on the

island of Hawaii.

The basic data used in this report are hourly rainfall amounts, in

inches, measured at the National Weather Service first order station at

the Hilo airport from 1953 through 1971. The information is available

as a part of the one-page summary, "Local Climatological Data," published

monthly by the National Weather Service. Reported rainfall amounts are

those measured during the clock hour. There is no information in the cited

publication on instantaneous rainfall rates.

CLIMATOLOGICAL SUMMARY

The Annual Summary of the "Hilo Local Climatological Data," published by

the Environmental Data Service of the National Oceanic and Atmospheric Adminis­

tration, contains a synopsis of the Hilo climate, as well as that of the pub­

lished summary, together with additional data on the extremes of Hilo rainfall.

The state of Hawaii consists of eight major islands and 124 minor islands

with a total land area of 6,425 square miles and a coastline of 750 miles. The

island of Hawaii is by far the largest of the Hawaiian chain, with an area

of 4,038 square miles, more than twice the area of all the other islands

combined. It is diamond-shaped, about 93 miles long from north to south and

76 miles wide (Fig. 1).

2

Hawaii lies well within the belt of northeasterly trade winds generated

by the semi-permanent Pacific high pressure cell to the north and east.

The climate of the island is greatly influenced by its topography which is

dominated by the volcanic masses of Mauna Loa and Mauna Kea. The highest

point on the island, and in the north Pacific Ocean basin, is the 13,796-

foot summit of Mauna Kea closely followed by Mauna Loa which rises to

13,680 feet. Other major topographic features are Hualalai (8,271 feet),

the Kohala Mountains (5.480 feet) and Kilauea (4,090 feet). The island of

Hawaii is made up of these five volcanic mountains, their slopes, and the

broad saddles between them. Mauna Loa and Kilauea, which occupy the entire

southern half of the island, are still active volcanoes and, hence, smooth­

sloped in contrast to the deeply eroded valleys found along the slopes of

Mauna Kea and the Kohala Mountains.

The principal features of the island's climate are the marked varia­

tions in rainfall with location and elevation, the persistent northeasterly

trade winds in areas exposed to them, and the equable temperatures, both

daily and seasonally~ in localities near the coastline.

Over the island's windward slopes, precipitation occurs as a result

of one or a combination of climatic effects. Rainfall, in general, may

be related to (1) trade-wind showers, (2) frontal or cyclonic storms and

(3) intense convective storms referred to, for convenience, as thunder­

storms. High intensity rainfall is generally associated with the latter

two cases. Most precipitation on the windward coast, in terms of frequency of occur-

rence, takes the form of showers within the ascending moist trade winds. Mean

annual rainfall increases from 100 inches or more along the coasts to over 300

inches at elevations of 2,000 to 3,000 feet, and then declines to about 15 inches

at the summits of Mauna Kea and Mauna Loa. Leeward areas, the southern and

western sections of the island. are, in general, topographically sheltered

from the trades, hence from trade-wind showers, and are therefore drier.

Even in lee areas, however, afternoon and evening cloudiness and showers re-

sult from the onshore and upslope movement of sea breezes caused by the day-

time heating of the land.

Where mountain slopes are steeper, mean annual rainfall may range

from 30 inches along the coast to 120 inches at elevations of 2,500 to

3,000 feet. The driest locality on the island, and in the state, is the

OLiHUE

KAUAI

OAHU ~ MOLOKAI

HONOLULU /'-"--.,

'-----/~ LANAI <V ~

Q

MAUl

FIGURE 1. TOPOGRAPHIC ML\P OF THE ISLAND OF HAWAII.

3

4

coastal strip just leeward of the southern portion of the Kohala Mountains

and the saddle between the Kohala Mountains and Mauna Kea, whi.ch has an

average annual rainfall of less than 10 inches.

These contrasts in rainfall are reflected in the soil and vegetation,

which are characterized by frequent and abrupt transitions from lush

tropical growth to near-desert conditions, such as occurs between the wet

windward slopes of Kilauea volcano and the Ka'u desert just to the south.

Hilo is a small city (population of about 28,000) located near the

midpoint of the windward (eastern) coast of the island. Within the city

the average rainfall varies from about 130 inches near the shore to as much

as 200 inches in the higher elevations. The wettest part of the island of

Hawaii, with a mean annual rainfall exceeding 300 inches, is at an eleva­

tion of about 3,000 feet about 6 miles upslope from the city limits. It

rains on an average of about 280 days a year in the Hilo area.

Rainfall is measured in Hilo at several stations. Most of the data

used in the present report were obtained from records of the National

Weather Service's airport station for 1953 to the present. During this

period, the annual rainfall varied from a maximum of 173.23 inches (1969)

to a minimum of 71.40 inches (1962), the maximum monthly rainfall was 50.82

inches (December, 1954) and the minimum monthly rainfall was 0.36 inches

(January, 1953), and the maximum 24-hour rainfall was 15.70 inches (February,

1969).

Hawaii's equable temperatures are associated with its mid-ocean loca­

tion and the small seasonal variation in incident solar radiation. At Hilo,

the range in average temperature from February and March, the coldest

months, to August, the warmest month, is only 5.2°F and the average daily

range is approximately 15°F. The highest temperature of record at the Hilo

airport is 94°F; the lowest 53°F. Greater variations occur in localities

with less rain and cloud cover, but temperatures in the mid-90's and low

50's are uncommon anywhere near the coastline of the island.

The trades prevail throughout the year, although, because of large

scale climatic reasons, they may be absent for days or even weeks at a time,

particularly in the winter. The trade winds which are predominantly north­

easterly and their interaction with the topography have a profound influence

on the climate of the island. Places on the windward side of the island

exposed to the trades may be affected by local mountain circulations. For

example, the prevailing wind at the Hilo airport is not the northeasterly

trade, but the southwesterly wind that drifts downslope off Mauna Loa

during the night and early morning hours. The island's entire western

5

'(Kona) coast is sheltered from the trades by the high mountains. Occasionally,

however, unusually strong trade winds may sweep through the relatively low

(2,600 foot) saddle between the Kohala Mountains and Mauna Kea and reach the

a.reas to the lee.

Except for occasionally heavy rains, severe weather seldom occurs on

the island as a whole. During the winter, cold fronts or cyclonic storms

may bring high intensity rainfall to the island from the north or from the

south, often producing blizzards on the upper slopes of Mauna Loa and Mauna

Kea with snow extending downward at times to the 9,DOD-foot level or below

and icing near the summit.

Worthley (1967) studied the number and frequency of frontal passages

over the four principal islands of the Hawaiian chain from 1937 through

1966. His report on the study includes a variety of interesting relation-

ships in graphical form such as the mean monthly number of frontal passages

and the 3D-year frequency of frontal passages per winter season. Since the

number 6f frontal passages varies with latitude, Hilo is the least affected

of any of the stations (Lihue, Honolulu, Kahului, Hilo) and has the shortest

"winter season" (number of days between the first and the last frontal passage),

which lasts on an average of 140 to 145 days. Worthley's data on frontal

passages through the Hilo area were compared with monthly and annual rainfall

amounts measures at the Hilo airport. There appears to be no correlation

between the frequency of frontal passages with the December-January monthly

rainfall for Hilo during the 30-year period results in a curious inverse re­

lationship (see Table 1).

According to Table 1, if Hilo experiences two or more frontal passages

during the December-January period, the monthly rainfall is tess than would

be expected if there were no frontal passages, assuming no rain mechanism

other than the frontal passage. Data are not available to calculate the ef­

fect of frontal passages on daily rainfall amounts measured in Hilo. It is

probable that frontal passages increase the rainfall at other island stations

which are more exposed to the direct influence of winter storms.

Heavy rains also are produced as a result of intense convective activity,

6

TABLE 1. FRONTAL PASSAGES AND HILO RAINFALL (DECEMBER­JANUARY, 1937-66).

DEC.-JAN. MONTHLY FRONTAL PASSAGES NUMBER OF RAINFALL % OF MEAN

PER MONTH MONTHS (INCHES) RAINFALL

0 9 15.62 128

1 20 16.02 131 2 9 9.69 79 3 11 11.10 91 4 7 6.13 50 5 4 5.46 45

60 MEAN 12.25

which often occurs during the absence of the trade-wind inversion, which is

normally present at an elevation of about 6,000 feet. Such storms usually

are accompanied by electrical activity and are classified as thunderstorms,

even if lightning and thunder are not obvious. While Hilo averages only

8 thunderstorms per year, periods of enhanced convective activity can occur

particularly in the winter. For example, in the single month of January

1971, Hilo recorded 9 thunderstorms.

Lee (1967) studied the occurrence of thunderstorms in Hawaii and pre­

sented an analysis of monthly and diurnal thunderstorm and lightning dis­

tributions for the four pricipal islands of the state. He used data from the

the Hilo Airport station from February 1946 to August 1966 to plot the fol­

lowing variations for Hilo:

(1) Monthly distribution of thunderstorm days

(2) Diurnal distribution of thunderstorm occurrences

(3) Diurnal distribution of lightning occurrences

While Lee's data will not be repeated in this report, it is of interest

to summarize his principal findings with respect to thunderstorms in Hilo.

Lee notes that there are nearly equal numbers of thunderstorm days

during October, November, and December which increase rapidly to maximum

activity during February and March. Thunderstorm days decrease substantially

in April and May and reach a minimum during June through September. Hilo

thunderstorms are clearly a "winter-time" phenomenon, as indicated by the

fact that thunderstorm days during October through March are nearly four

times as numerous as during April through September.

7

The diurnal distribution of Hilo thunderstorms is distinctly bimodal,

with the primary maximum near 1500 local time, and a secondary maximum at

0300. Minimum activity occurs between 0700 and 1100 with little variation

between 1800 and 0200.

ANNUAL RAINFALL IN HILO

As previously noted, the annual rainfall in Hilo is highly variable.

Figure 2 shows the annual rainfall over the 40-year period from 1931 to

1970. The values plotted on the graph are from the Annual Summary of the

"Local Climatological Data" for Hilo, Hawaii, 1970.

Rainfall measurements during this period were made at two different

locations. From 1931 through April 1942 and from January 1945 through

February 1946, rainfall data shown in Figure 2 were recorded at the

Federal Building in downtown Hilo at an elevation of 40 feet above sea

level. All other values were measured at the Hilo airport, approximately

2 miles east of the Federal Building site. While minor changes in the

location of the rain gauge occurred during the 1940's and early 1950's,

the instrument has been in a relatively fixed position since February

1954. The Hilo Airport station is located at 19°43'N, l55°04'W, at an

elevation of 27 feet above sea level.

The mean annual rainfall during the period 1931-1970 was 136.18 inches

(the currently used climatolo"gical mean annual rainfall is 136.62 inches).

Except for the three-year period of 1936 to 1938, when the annual rainfall

measurements exceeded 180 inches each year, records obtained from the

Hilo Federal Building appear comparable to more recent ones from the

airport station.

During 1953 to 1971, the average annual rainfall was 133.86 inches.

Values ranged from a high of 173.23 inches (129 percent of the average) to

a low of 71.40 inches (53 percent of the average). Twelve of the 19 years

of record fell within 20 percent of the average rainfall amount.

The insert in Figure 2 indicates the annual rainfall frequency at the

Hilo airport over the interval of 1953 to 1970. The frequency is defined

fI) LIJ

is ~

.. ..J ..J

~ z <t a: ..J <t :::;) Z Z <t

200

160

80

HI LO FEDERAL BLDG. If .--,.. AIRPORT •

I I AIRPORT

t­Z LIJ () a:: LIJ a..

· · · · . . ANNUAL RAiNFALL FREQUENCY

500

400

(f)

ffi t­LIJ

300::E t= z LIJ ()

200

o iii i 0 1930 1940 1950

YEARS 1960 1970

FIGURE 2. ANNUAL RAINFALL IN HILO FOR 1931 TO 1970. INSERT SHOWS RAINFALL FREQUENCY (RATIO OF RAIN PLUS TRACE HOURS TO TOTAL HOURS) FOR EACH YEAR FROM 1953 TO 1970.

00

9

by the ratio of the number or rain hours to the total number of hours

in the year. A rain hour is any clock hour in which rain was recorded at

the airport station and includes both measurable and trace rainfall amounts.

As the graph indicates, rain fell at the Hilo airport during approxi­

mately one-third of all the hours in the 18-year period. On the average,

96 percent of all rain hours indicate light rains of lees than 0.25 inches

recorded in a clock hour. These light rains contributed approximately

62 percent of the total rainfall during the period. On the other hand

heavy rainfall, defined as more than one inch in a clock hour, accounted

for slightly more than 5 percent of the total precipitation, yet occurred

in less than 0.2 percent of the hours in the year.

The relative constancy of the annual rainfall frequency indicates the

necessity of investigating rainfall rate as the dominant factor contributing

to the total amount of rainfall in Hilo. If rainfall occurs at the Hilo

airport during approximately one-third of all the hours, year after year,

then the high variability in the annual rainfall can only be due to variations

in rainfall intensity. Furthermore, the relative constancy of the annual

frequency indicates that most rainfall in the Hilo area probably is produced

by a simple and regular physical process, possibly ralated to the local

wind circulation.

In his investigation of the association of synoptic and local wind

circulations with diurnal rainfall over Malaya, Ramage (1964) found that

the rainfall variation was substantially controlled by local wind changes

within the prevailing flow. It appears that similar relationships may

exist on the windward coast of the island of Hawaii.

To more fully investigate the variation in the annual rainfall in Hilo

with rainfall rate, the hourly precipitat~on data have been divided into

four intensity categories: 0.01 to 0.24 inches per clock hour, 0.25 to

0.49 inches per clock hour, 0.50 to 0.99 inches per clock hour, and rainfall

of 1.00 or more inches per clock hour and tabulated (Table 2).

Figure 3 shows the percentage of the total annual rainfall in each of

the four intensity categories for each year in the period 1953-1970 (note

that 1971 is not plotted). Table 3 shows the average contribution of each

intensity category to the annual rainfall and the range of values about

the average. It is interesting to observe that heavy rains of one or more

inches per clock hour, while occuring on an average of only five hours per

L&J o 0::: L&J a..

.. ..J ..J

80

60

........ Of .. " ........... .

:. ..... ..- ... . :" If". .: •••• .. •••• :.. • ••

0.01 - 0.24 IN I HR

0.09 § o :t:

: 40 ...... .: •.. ..- a.. ........ .*.......... ...... . ...... _

." •••• *, .* *. .. .. .. •• : A, ._.. : z -<[ 0:::

i -: a.. ..a -". .: : a". .. •••• _ ••

.. .. .. .." .. ~ : .... .:" MEAN ANNUAL RAINFALL RATE

0.07 (/) L&J :t: o Z ':

----...... ' 0.05 ..J <[ :::J Z Z <[ 20 0.25 - 0.49 IN I HR

0.50-0.99 IN/HR

::: 1.0 IN I HR o , ¥

1955 1960 1965 1970 YEAR

FIGURE 3. PERCENTAGE VARIATION IN THE ANNUAL RAINFALL IN HILO IN FOUR INTENSITY CATE­GORIES (1953-1970). INSERT SHOWS THE MEAN ANNUAL RAINFALL RATE (TOTAL RAIN­FALL DIVIDED BY TOTAL HOURS OF MEASURABLE RAIN).

..... o

TABLE 2. RAINFALL DATA BY INTENSITY CATEGORIES

INTENSITY CATEGORIES

1 IN./HR. 0..50.-.99 IN./HR. 0.25-.49 IN./HR. 0.0.1-.24 IN./HR. RAINFALL AMOJNT AMOUNT AMOUNT AMOUNT TRACE TOTAL RA I NFALL FREQUENCY

YEAR (INCHES) HRS. (INCHES) HRS. (INCHES) HRS. (INCHES) HRS. (HRS.) (INCHES) (HOURS) %

1953 4.8 3 9.65 13 10..24 32 65.27 1403 1321 89.64 2772 31.64

1954 19.27 14 23.18 35 33.94 10.0. 85.94 1692 10.89 162.33 2930. 33.44

1955 0. 0. 8.0.9 11 29.12 82 86.21 170.2 1351 123.42 3146 35.91

1956 9.16 6 28.18 43 40..33 121 90..61 1715 1233 168.28 3118 35.50.

1957 8.0.9 6 14.78 23 26.44 80. 89.95 1750. 1305 139.26 3164 36.12

1958 1.58 1 10..38 17 17.34 51 76.60. 160.4 1247 105.90. 2920. 33.33

1959 10.12 8 13.82 20. 18.32 54 75.55 1654 1242 117.81 2978 34.0.0.

1960. 9.45 6 17 .33 26 26.0.4 78 94.10. 1693 10.21 146.92 2824 32.15

1961 3.30. 2 14.15 21 21.67 66 80..53 1590. 1236 119.65 2915 33.28

1962 1.0.4 1 3.17 5 9.67 31 57.52 1316 1277 71.40. 2630. 30.0.2

1963 6.27 4 16.10. 24 29.18 87 73.43 1460. 10.84 124.98 2659 30..35

1964 5.31 4 24.0.2 37 33.37 102 103.78 1987 118a 166.48 3310. 37.68

1965 10..91 9 20..99 32 23.0.4 66 72.33 140.2 1151 127.27 2660. 30..36

1966 9.28 6 11.53 18 25.33 75 n.87 1540. 1264 124.0.1 290.3 33.13

1967 6.83 5 24.91 36 38.32 111 83.94 1482 10.0.9 154.0.0. 2643 30..17

1968 8.96 7 16.51 25 37.n 112 70..90. 1321 10.0.9 134.14 2474 28.16

1969 13.49 10. 29.18 42 38.42 114 92.14 1657 949 173.23 2772 31.64

1970. 4.70. 4 26.68 39 32.39 94 90..21 1736 10.25 153.98 2898 33.0.8

1971 4.25 3 23.41 36 34.96 124 77 .99 1547 10.27 140..69 2737 31.24

TOTAL 136.49 99 336.14 50.3 525.89 1580. 1544.87 30.251 220.20. 2543.39 54453 621.20.

YEAR 7.18 5.21 17.69 26.47 27.68 83.16 81.31 1592.16 1158.95 133.86 2865 32.69 f-' f-'

til! ""411l<V,,,t.:::mH' •• ~ .".,,,·m",,,"~_z:;· """"'"'

12

TABLE 3. PERCENTAGE AMOUNTS Al\lD FREQUENCIES BY RAINFALL RATE.

RAINFALL RATE AMOUNT (PERCENT) FREQUENCY (PERCENT) (INCHES/CLOCK HR.) AVERAGE RANGE AVERAGE RAN:;E

TRACE AMOUNTS 41 34 - 48 0.01 - 0.24 62.3 53 - 80 55 50 - 60

0.24 - 0.49 19.9 12 - 28 2.8 1.2 - 4.5 0.50 - 0,99 12.5 4.5 - 16.8 1.0 0.2 - 1.5

> 1.00 5.3 0 - 12 0.2 0 - 0.4

100.0 100.0

year, contribute about 5 percent of the annual rainfall.

The insert diagram in Figure 3 shows the mean rainfall rate; that is,

the annual rainfall divided by the total hours of measurable rain. Since

light rains constitute the major contribution to the total rainfall in

Hilo, it is not surprising that the rainfall rate curve is approximately a

mirror image of the 0.01 to O.~4 inches per hour intensity curve. The

average rainfall rate is 0.078 inches per hour and the rate varies, as

would be expected, from 0.053 inches per hour in the year of minimum

rainfall (1962) to 0.095 inches per hour in the year of maximum rainfall

(1969). While rainfall rate is probably a meaningless expression when applied

to periods of one year, the variations in the rate indicate the relative

importance of the different rainfall categories. For example, during 1962

and 1967, while the rainfall frequency was approximately the same (30 per­

cent), the recorded rainfall in 1967 (154.00 inches) was more than twice

that of 1962 (71.40 inches). In 1962, approximately 80 percent of the

total rainfall was from light rains, while the corresponding value in 1967

was 54 percent. Annual frequency relationships for the various rainfall intensity

categories are shown in Figure 4. The number of hours of trace rainfall

and measurable rainfall in each of the intensity categories is expressed

as a percentage of the total rain hours in each year and plotted on a

logarithmic scale. Averages and ranges of values are given in Table 3.

The curve labeled "rainfall frequency (all hours)" shown in Figure 4

is for comparison with the other curves, although it is derived

13

100

0.01- 0.24 IN I HR

••••••••••••• ~:: • .:.:.:.::~: ....................................... )1'0(. •••••••••••••••••••••••••••••••••••• TRACE AMOUNT

----- ---------............ ---/ " ................................................ --- RAINFAll FREQUENCY

(All HOURS)

... Z I.IJ U 10 a: I.IJ a..

-..J ..J

~ z <i a: 0.25-0.49 IN I HR

u. 0

)-u Z I.IJ ::> 0.50 -0.99 IN I HR 0 I.IJ a: u.

2: 1.0 IN/HR

1955 1960 1965 1970 YEAR

FIGURE 4. PERCENTAGE VARIATION IN ANNUAL RAINFALL FREQUENCY IN HILO IN FOUR INTENSITY CATEGORIES AND TRACE AMOUNTS. THE CURVE LABEL­ED "RAINFALL FREQUENCY (ALL HOURS)" IS THE SAME AS THAT SHOWN IN THE INSERT IN FIGURE 2.

14

in a different way. It is the same curve shown in the insert box in

Figure 2, and it thus indicates the percentage of rain hours in the year.

MONTHLY RAINFALL IN HILO

Firgure 5 is a plot of the Hilo monthly rainfall during the 40-year

period 1931 through 1970. As previously mentioned, data were taken at the

Hilo Federal Building from 1931 through April 1942 and from January 1945

through February 1946. All other rainfall data were measured at Hilo air­

port. Monthly amounts in excess of 40 inches were recorded during five

months: March 1939; March 1942; December 1946; December 1954; and February

1969. There were also four months in the 40-year period when the monthly

rainfall was less than one inch: January 1940; February 1941; January 1953;

and December 1963. It is interesting to note that all of the monthly ex­

tremes occurred during the winter season in Hilo.

The 40 years of record for each calendar month were divided into three

groups: the 10 years with the highest monthly rainfall (upper quartile),

the 10 years with the lowest monthly rainfall (lower quartile), and the

intermediate 20 years of record. This information is plotted in Figure 6,

which may be considered a monthly rainfall expectancy graph for Hilo.

The maximum monthly rainfall, 50.82 inches, occurred in December 1954

and the minimum, 0.36 inches, occured in January 1953. The months of

highest rainfall, both in the maximum recorded amount and in the upper

limit of the 50 percent section, are February, March, and December. If

the February monthly rainfall is normalized to 31 days (for better compari­

son with the March and December data), it exceeds the amount measured in

March. The two months which have the highest normalized rainfall are

December and February. The decrease in monthly rainfall in January, occur­

ring in mid-winter and directly between the two months of highest rainfall,

is probably a result of the reduced rainfall frequency in January (see

Figure 8, p. 19).

The months of lowest mean rainfall amount in Hilo are June, July, and,

September. Since Figure 6 was drawn, three new monthly lows have been es­

tablished and have been added to the figure.

Figure 7, showing the maximum 24-hour rainfall in each month, is plotted

LEGEND:

C VALUES > 40" 40-1 4 VALUES < I"

20

f3 oJ liiii","""';""""";""""'" ',j,,', j"""""""""';"""":;""""""""""'"Iliii~""'it"'~ii"i"'ii"'i""'t'i'[""i"'[i'i'1""""""-"""'1"";"""1"""""'1""""i"I"""""'I"'I"""" ::I: 1935 1940 1945 1950 U ~

40

20

o I';'; iiii 'ii,""""""'." Ii ii;I 'I'i" "iiii' ii"" "; "I' Ii Ii Ii "il'i" "t:';II" " "iil" II ": Ii "1,1 •• Ii' Ii iii. t """; 'I II' Ii" "i~ iiii. ".4." Ii"" Ii iii Ii' 'i' 'i,i Ii' 'i; "1"""""" Ii;: Ii' li'I',II:' II: iii., I';" 1955 1960 1965 1970

FIGURE 5. MONTHLY RAINFALL FOR HILa (1931 TO 1970). ~

U1

16

C/) I.LJ % 0 Z

. -J -J

~ Z <t p:

~ % t-Z 0 ::i

60

40

20

RANGE OF MONTHL( RAINFALL DURING 50"0 OF YEARS OF RECORD l

EAN MONTHLY VALUES USED BY NATIONAL WEATHER SERVICE

1971 • 1971

150

00

50

O~~--~~~~=T--r-~~~~~--~~--~--O J F MJ J AS 0 NO

MONTHS

FIGURE 6. QUARTILE DISTRIBUTION OF RAINFALL IN HILO BY MONTH (1931-1970) •

C/) 0::: I.LJ t-I.LJ ~

t-Z I.LJ 0

17

in the same fashion as Figure 6, except that the period of record considered

is 1953-1970. The months of highest 24-hour rainfall are February and

November, while the lowest 24-hour maximum rainfalls were recorded in

January and December. Excluding the high rainfall months of February and

November and the lower summer months of June, July, and September, all

maximum 24-hour rainfall amounts fall in the range of 9.5± O.S inches.

The concentration of heavy rainfall in the winter months is shown

clearly in Figure 8, where the total rainfall in the IS-year period,

1953 to 1970, is plotted by month and by intensity category. More than

75 percent of the total rainfall in June, July, and September is associated

with light rains, i.e.~those less than 0.25 inches per clock hour. On the

other hand, about 50 percent of the monthly rainfall in February and

November is associated with rainfall of more than 0.25 inches per hour.

Figure S also indicates the monthly frequency of rainfall in the Hilo

area. Whi 1 e 1 es s than 25 percent of t.he January hours are rain hours,

rain falls in more than 35 percent of the hours in April, May, and August.

DIURNAL RAINFALL IN HILO

More than 160,000 hours of rainfall data recorded by the National

Weather Service at the Hilo airport have been used to construct diurnal

rainfall graphs. Hourly rainfall amounts have been divided into the four

intensity categories previously described and plotted by month. The

January through June graphs (Figures 9 through 14) show total rainfall for

each hour of the day over the 19-year period from 1953 through 1971. The

graphs for July through December (Figs. 15 through 20) are for the IS-year

period from 1953 to 1970.

On an annual basis, heavy rains may occur during any hour of the day,

particularly in the winter months. During the entire period of record

studied, there were no heavy rains recorded in June and only one such event

in July. Furthermore, in the daytime hours between OS 00 and 1400, there

was only one hour of heavy rainfall recorded during the six-month period

from May through October. Heavy rains occur most frequently in the hourly

periods ending at 0800, 1500, lSOO, and 2200 local time.

The data demonstrate convincingly that the annuaZ diurnal rainfall

curve for Hilo exhibits a minimum in the afternoon, between 1400 and 1500

hours. This effect, however, is masked during the winter months by the

18

en LaJ :::t: 0 z

.. ::t ~ Z « a: a: ::l 0 :::t: I

V

'" :E :l :E x « ~

15

10

5

JANGE OF MAXIMUM 24-HOUR RAINFALL RECEIVED DURING 50"0 OF THE YEARS OF RECORD. J

• 1911

J A SON 0

MONTHS

40

30

en 0: LaJ t-LaJ

20 :E t-z LaJ 0

10

FIGURE 7. QUARTILE DISTRIBUTION OF MAXIMUM 24-HOUR RAINFALL IN HILO BY MONTH (1953-1970).

t-Z W 0 0:: W Q. .. ~ g w ~ 0

>-t: (f) z W t-Z -~ ...J ...J

~ z <t 0::

b J: t-Z 0 ::IE

30

J

MONTHS

o N 0

19

0.01-0.24 IN/HR

MONTHLY FREQUENCY

OF RAINFALL

0.25 - 0.49 IN I HR

0.50-0.99 IN IHR

~ 1.0 IN I HR

FIGURE 8. PERCENTAGE VARIATION IN MONTHLY RAINFALL AMOUNTS IN HILO BY FOUR INTENSITY CATEGORIES (1953-1970).

20

relatively heavy rainfall associated with synoptic disturbances and con­

vective activity. It is difficult to see any particular diurnal pattern

in the January and February rainfall (Figs. 9 and 10). The tendency toward

decreasing afternoon precipitation, particularly of the light rains, begins

to appear in the diurnal graph for March (Fig. 11). The months of May

through October (Figs. 13 through 18) illustrate clearly the normal summer­

time diurnal variation in Hilo rainfall. This pattern also can be seen in

the November graph (Fig. 19), although not as distinctly, and by December

(Fig. 20) the predominantly winter-type rainfall again complicates the

simple nighttime maximum-daytime minimum relationship.

The graph for August (Fig. 16) illustrates a diurnal pattern frequently

observed in Hilo. In addition to the afternoon minimum, the rainfall often

shows two maxima, one in the early evening between 2000 and 2300 and another

in the early morning between 0300 and 0500.

The diurnal variation in rainfall frequency also has been calculated for

each month. The frequency curves have not been reproduced in this report

since they are quite similar to the diurnal variation in light rainfall amounts.

The boundary between the shaded and unshaded portion of each diurnal curve

(Figs. 9 through 20) may be taken as a close approximation to the frequency

curve for that month. This result might be anticipated, since more than 93%

of the hours of measurable rain are hours of light rainfall, that is, less

than 0.25 inches per clock hour.

The monthly diurnal graphs may be combined to study seasonal variations

or to derive an annual curve. Such a curve has been plotted for each year

from 1953 to 1970. While the curves have not been reproduced in this report,

it is of interest to note that they are quite similar to one another, year

after year. The annual rainfall amounts vary widely, but the diurnal pattern

persists. This fact suggests, as does the relative constancy of the annual

rainfall frequency, that Hilo rainfall is produced by a simple and regular

process. The details of the physical mechanism underlying rainfall in Hawaii

are currently being investigated at the Cloud Physics Observatory.

OTHER SOURCES OF INFORMATION

ProbablY the best single source of data on rainfall in the State of

Hawaii is Taliaferro's (1959) RainfaZZ of the Hawaiian IsZands. Taliaferro

CJ) L&J ::t: (,)

z ..

..J

..J ct LL. z ct a::

..J

~ ~

LEGEN D: .40 15..., RAINFALL DISTRIBUTION

1.0 OR MORE IN IHR

0.50 - 0.99 IN IHR

nf{~:1 0.25 - 0.49 ~30

IN I HR

10~ I I 0.01 - 0.24 IN I HR

20

5

I ~r:-:-:-:;l"""1 ~ t:;::}::]:::::::}]}::~;::]::':::':·:·:·:1 I::::; ;[}}:F';':':':':~ I:::::::;::::l~~:::::it;,··········r·;,;,:·:·:·r··· ..... ;:~ ~IO

4 I 0

o 24 20 8 12 16 LOCAL TIME, CLOCK HOURS

FIGURE 9. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: JANUARY 1953-1971.

~~~~~~~'~~~'llWmn"~=-E:==maED"" __ PB __ _

CJ)

a:: L&J t-L&J ::E t-z L&J (,)

N .....

(J)

w !r 0 z -

.. ...J ..J

~ Z <i 0::

...J <l I-0 I-

20, LEGEND: RAINFALL DISTRIBUTION

1.0 OR MORE IN/HR

0.50 - 0.99 IN IHR

0.25 - 0.49 IN/HR I 40 15~ - r:';';-;'1

0.01 - 0.24 IN/HR • '---I

- I .. ···· ........ 1m:: :1 1-30

10

20

5 p:::::::q I}~\:})\::::::] 11 10

20 I 0 o M 4 8 12 16

LOCAL TIME. CLOCK HOURS

FIGURE 10. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: FEBRUARY 1953-1971.

"1',)-

IV

(J)

0:: W I-w :::E I-Z ll.I 0

C/) I.&J :::t: 0 z

.. ..J ..J e( La. z e( 0:::

..J e( I--0 I--

LEGEND: .40 151

RAINFALL DISTRIBUTION - 1.0 OR MORE IN IHR

0.50 - 0.99 IN IHR .······1 ~30 ...... ......

r"J 0.25 - 0 49 INI HR ......

~ ...... '.:-:.:.:.:.: .. ... , .. ...... 0.01 - 0.24 :::::: ;::::: IN I HR ...... -_ ... _,. ....

10 ----_._ .. - ----------------

;:::::;:;:::;: ...... ::: ~:::::::::: ::;: ::: :::: :~:

••••••••••••••

20

-5

.... ·1:~r?:::I::::: :f~:::~::::}I::::::::::::::[:::::::::J:::::::::::::J 1-10

o ~

4 16 ..... _~.1 ~LLL~~---.-l----'-----:2~4 0

8 12 20 LOCAL TIME, CLOCK HOURS

FIGURE 11. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR INTENSITY CATEGORY: MARCH 1953-1971.

SHOWING TOTAL RAINFALL PER CLOCK HOUR BY

C/) 0::: I.&J I--I.&J :::E l-Z I.&J 0

N VI

C/) W IX: (.) z

.. ...J ...J e( I.L. Z e( 0::

...J e( I-10 I-

20.., LEGEND: r 50 RAINFALL DISTRIBUTION

1.0 OR MORE IN IHR

0.50 - 0.99 IN IHR

r::::::::::1 ~:~~ ~ ~::: IN I HR ~40

15 1 ~ IN I HR ............ ...... '" .. "

30

10

20 [':'~':':':':'~'.';~~':'~'~';;J a..:...:...:...:·:·:·>:':·:·l·:-:·:·:~:·:·:t~·~·~·~·~·:·~~~ '" '" '" '" ~I I::';';;;; :1"''''' ··"'1 ..... '" •• :':':':':':':.(':':':':':';'~'~':'~.;';';'J'.'.'.'.'.'.'.1 •.... " ... -.-.-,

5 r:<:<:<:<:<r:::::::::::I::::: :1:::::::::::::[:~:~:~:~:~l::::~:~:::l~:)~{:rI

10

I 0 o ' 24 4 8 12 16 20

LOCAL TIME, CLOCK HOURS

FIGURE 12. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: APRIL 1953-1971.

N ~

C/) 0:: W I-ILl :E -l-Z ILl (.)

LEGEND: .40 15., RAINFALL DISTRIBUTION

1.0 OR MORE IN I HR

0.50 - 0.99 IN I HR ........... . _······1 ...... bd-30

J I roo r:1........... .. ........ .. Ul ,',',','0',·, .... ooL """"'.'.' 0 25 0 9 f N H ................. .

~ ~}» :~m; >~<{ . -.4 I R o (~}) "" ........ ::::: 001 - 024 IN I HR z ::;:::::;:::: :::::: :::::: ::::: ...... . . 10 .:-;.;.:.:.; ...... .I ...... <........... . ................. , ............ ' ........ , ·L·.·.·.·.·.·.·. (f)

.. 0:: ~ ~ ~ ~

~ 20 ~ z -- ~ ~ Z 0:: ~

............. ~ 0 ~ 5 j:! ~ t F.;~F::;:::::;:;I;'~ .. :'~ __ F~:::~:~:~:I:;::;::::}:I 1-10

0----'-----" 4 8 12 16

LOCAL TIME, CLOCK HOURS 20

I 0 24

FIGURE 13. MONTHLY DIURNAL RAINFALL DISTRIBUTION. FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: MAY 1953-1971.

_+~~~.!I':.~ :iiUilllitlii!ilOtililill!Giii""""

tv (,n

(J)

'" ~ 0 z

.. ....J ....J « I&. z « a: ....J « I-0 I-

15

10

:«f~

5 ~~~}~~~}~~i :::::::::::::.i

LEGEND: RAINFALL DISTRIBUTION

":':~:':':':-:':';';':':"

1.0 OR MORE IN / HR

0.50 - 0.99 IN / HR

0.25 - 0.49 IN / HR

0.01 - 0.24 IN / HR

::.:.:.:.~

40

30

en a: '" ~ I-:::::. :::::. '"

::x::::t:t:«ff 2 0 ~

10

I­Z kI o

I 0 o 24 4 8 12 16 20

LOCAL TIME, CLOCK HOURS

FIGURE 14. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: JUNE 1953-1971.

N 0\

I 0 o 24 4 8 12 16 20

LOCAL TIME, CLOCK HOURS

FIGURE 15. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: JULY 1953-1970.

N "-I

en W :I: u z

.. ...J ...J

~ z ct a::

...J

~ 0 ....

LEGEND: ,40 15..., - RAINFALL DISTRIBUTION

1.0 OR MORE IN IHR

0.50 - 0.99 IN IHR

Mr:-?!::: :::L:»~ L:}}I 0.25 - 0.49 IN I HR ~······I ............. ~30

I 0 -r[:::~:[[::[:E[:[::::::::I[:[:::::~:~r:::::~~[:~\:rn:~:~:~::~:~:l:::::::::::::1 U 0.01 - 0.24 IN I HR - ................ •. -.--'_Y_'-'--.,

....... ; \ :;;;;: ::: • ••••••••••••

·\I:I:·~I~~~I~ ~m~~~~~~~~~~ ...... 20

.......

5

1:?W:1 · .... ·1· .. · .. 1 .:::-:.:::.:~ :::::: f-IO

0~-L~~~~L-~~~~~~--L-~~~~~--~~~~~~-;;24 0 4 8 12 16 20

LOCAL TIME, CLOCK HOURS

FIGURE 16. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: AUGUST 1953-1970.

N 00

en a:: w .... w ~ -.... z w u

rn LLI ::z:: 0 z

.. ..J ..J

~ z « a: ..J « .... 0 ....

LEGEND: r40

15l RAINFALL DISTRIBUTION - 1.0 OR MORE IN IHR

0.50 - 0.99 IN IHR

tfI tf} 0.25 - 0.49 IN I HR 1-30

0.01 - 0.24 IN I HR 10

20

5

r-1 II r;·:·:·;.:·l··········l ........ .i - ~ ...... , ::::: ~

, ...... , 1-10

4 1 I 0

01

U 8 12 16 20 LOCAL TIME, CLOCK HOURS

FIGURE 17. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: SEPTEMBER 1953-1970.

~.".~"'~).:i';;;$:h::w>,,:;;;:a;;;;;;;s:::.:::;;:;:;:::;;wz:m:tiiRQ£ swz:::;u::u:;;; _ZW !&£

(f)

a: w ~ w ::t ~ z w 0

N \0

en ILl ::r::: 0 Z

.. ...J ...J

~ z -<t a: ...J <t I-0 I-

LEGEND: r-40 15, RAINFALL DISTRIBUTION

1.0 OR MORE IN IHR

0.50 - 0.99 IN IHR

lol ......ITITITIl 1-30

~ - ........... ;:::;:;:::;: 0 25 - 0 49 IN I HR

............ .:-:.:.:-:-:" ..

0.01 - 0.24 IN I HR _ •••••• __ • ____ I_;.~~ __ •• ____ .. I:·~··-

20

1·· .... 1 ........ I' ..

5

h:;:;:=:;:;:[{::::=Lj{{:}j;:;; ~ :1 r}}~rI 1-10

01-~JL-L-L-L~~~~~~~L-L-L-~~~~~~~~~-2~40 4 8 12 16 20

LOCAL TIME, CLOCK HOURS

FIGURE 18. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: OCTOBER 1953-1970.

CA 0

en a: ILl I-ILl :E ~ z LLI (J

C/) LLI J: U Z

.J'

...I

~ z <[ 0:

...I

~ 0 I-

20.., LEGEND: RAINFALL DISTRIBUTION .50

1.0 OR MORE IN IHR

0.50 - 0.99 IN IHR

15~:::. 0.25 - 0.49 IN/HR - ~40

':: : r····1 0.0 I - 0.24 :::::.:: : IN I HR ...... :: . ........ :

1::::::::::::3::::::1,""'1..-- j;;;;;;I::::::_::::::L 30

10

20

5 ~:;}::;:::F::>~:;l:::;:;::d~:;:::::J;;:;; :I

10

0 ......... --11-----'-----1---'---'

4 8 12 16 _LJ....---.lL--L--'-_~-------=-1 0 L_L...---.L_-'--~_ 24

20 LOCAL TIME, CLOCK HOURS

FIGURE 19. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: NOVEMBER 1953-1970.

(J) 0: LLI I-LLI :!: j:: z LLI u

tN ......

(I) LIJ :J: (,) z

.. ..J ..J <t I.L Z

C2 ..J

~ 0 t-

LEGEND: RAINFALL DISTRIBUTION

1.0 OR MORE IN IHR

0.50 - 0.99 IN IHR r 40 15.., M:1N:~ 0.25 - 0.49 IN I HR

0.01 - 0.24 IN I HR

111_ '--'

IillTIL I!:::::~;~~~:I ::::::1- 30 -10 ,. ,. ~ ... ,. .......

20

5 ,..-".", ... , r·········1 """"1 1-10

o 0 4 8 12 16 20 24

LOCAL TIME, CLOCK HOURS

FIGURE 20. MONTHLY DIURNAL RAINFALL DISTRIBUTION FOR HILO SHOWING TOTAL RAINFALL PER CLOCK HOUR BY INTENSITY CATEGORY: DECEMBER 1953-1970.

--<A N

(I) cr I.LI t-LIJ ::Ii i= Z LIJ (,)

33

presents annual and monthly median isohyetal maps for the islands of Hawaii,

Maui, Molokai and Lanai, Oahu, and Kauai, based on data for the 25-year

period, 1933 to 1957. In addition, he provides tables of median and extreme

monthly rainfall amounts and median, upper and lower quartile, and extreme

annual rainfall amounts for approximately 1400 active and discontinued rain

gauges. The compilation includes an index of rain gauges, along with loca­

tor maps, and a useful bibliography of 88 publications related to Hawaiian

rainfall.

The Department of Land and Natural Resources of the State of Hawaii

has published An Inventory of Basic Water Resources Data: IsZand of Hawaii

(1970). The report contains monthly and annual rainfall amounts for more

than 100 stations and an isohyetal map of the island showing mean annual

rainfall during 1931 to 1960, based on records from 97 gauges. Additional

selected data on temperatures, evaporation, wind, humidity, stream flow,

ground-water resources, and water quality are also provided.

A valuable source of literature on rainfall and other weather phenomena

in Hawaii has been compiled by Ekern and Worthley (1968). In most cases

the author's abstract or a brief description of the paper is given.

ACKNOWLEDGEMENTS

It may please (or perhaps shock) the reader to learn that the data

presented in this report were not processed by computer. The author is

indebted to Myra Enriques, Melody Meier, Florence Miyamoto, Margaret Okumoto,

and Sue Nakashima for their countless hours of dedicated data reduction.

Thanks also go to Bob Mitchel, who did most of the drafting, and to Darla

Serrao who typed the manuscript.

Raymond Busniewski of the Hilo airport station of the National Weather

Service furnished most of the data. The author has profited from helpful

discussions with Howard Ellis, of Mauna Loa Observatory, James Hunter, of

Beaumont Agricultural Research Center, and with David Raymond, Tsutomu

Takahashi, and Ronald Taylor of the Department of Meteorology, University of

Hawaii.

34

REFERENCES

Ekern, P.C. and L.E. Worthley. 1968. Annotated bibliography of publica­tions and papers relevant to Hawaiian weather. Hawaii Institute of Geophysics Technical Report 68-11, University of Hawaii. p. 126.

Lee, C.B.H. 1967. "A preliminary study of thunderstorms in Hawaii," In Weather Phenomena in Hawaii. Hawaii Institute of Geophysics Technical Report 67-9, University of Hawaii. p. 41-53.

Ramage, C.S. 1964. "Diurnal variation of summer rainfall of Malaya." J. Trop. Geog., University of Singapore and University of Malaya. Vol. 19. p. 62-68.

State of Hawaii, Department of Land and Natural Resources, Division of Water and Land Development. 1970. An inventory of basic water resources data: island of Hawaii. Report R34. p. 188.

Takahashi, T. and C.M. Fullerton. 1972. "Raindrop charge-size measure­ments in warm rain." J. of Geophys. Research, Vol. 77, No.9. p. 1630-1636.

Taliaferro, W.J. 1959. RainfaU of the Hawaiian islands. Hawaii Water Authority, State of Hawaii, Honolulu. 394 p. (This book is out-of print. It is currently being revised, expanded, and updated by com­puterized methods.)

U.S. Department of Commerce, National Oceanic and Atmospheric Administra­tion, Environmental Data Service. 1970. Local climatological data, annual summary with comparative data, Hilo, Hawaii. 4 p. (In addition, weather parameters including hourly rainfall, as measured at the Hilo aiport station.)

Worthley, L.E. 1967. "Synoptic climatology of Hawaii", in Weather pheno­mena in Hawaii. Hawaii Institute of Geophysics Technical Report 67-9, University of Hawaii. p. 1-40.