HEAVY RAIN EVENTS PRECEDING THE ARRIVAL OF TROPICAL CYCLONES
Matthew R. Cote, Lance F. Bosart, and Daniel KeyserDepartment of Earth and Atmospheric Sciences
University at Albany/SUNY, Albany, NY
Michael L. Jurewicz, Sr.National Weather Service Forecast Office
Binghamton, NY
CSTAR II Grant NA04NWS4680005
8th Northeast Regional Operational Workshop 2 November 2006
• Observations
- Predecessor rain events (PREs) form with some regularity well in advance of tropical cyclones (TCs)
- Rainfall can be at least as significant as that directly associated with the TC
• Forecasting Issues- Most operational focus on track and intensity of the TC itself when PREs occur
- Heavy rain in advance of the TC may increase flooding risks
- Flooding may occur where it was otherwise not expected
OVERVIEW AND MOTIVATION
• Demonstrate the PRE identification process
• Present preliminary climatological results
• Follow the evolution of the PREs associated with Katrina (29-30 August 2005)
• Compare the synoptic setup surrounding Katrina with that of the null case of Cindy (6-7 July 2005)
GOALS
IDENTIFYING PREs
• Coherent area of rain displaced downstream from the parent TC
- NCDC and WSI NOWRAD radar imagery - NHC best-track data
• Normalized rainfall greater than 100 mm/day- NPVU QPE archive - NWS text products
• Diagnosis of important synoptic-scale features- NCEP/NARR gridded datasets
PRE
EXAMPLES OF PREs
1800 UTC 05829 WSI NOWRAD 2 km US Radar Mosaic
EXAMPLES OF PREs
PREs
0900 UTC 05830 WSI NOWRAD 2 km US Radar Mosaic
0
1
2
3
4
5
6
21-3
0 A
pr
1-10
May
11-2
0 M
ay
21-3
1 M
ay
1-10
Jun
e
11-2
0 Ju
ne
21-3
0 Ju
ne
1-10
Jul
y
11-2
0 Ju
ly
21-3
1 Ju
ly
1-10
Aug
11-2
0 A
ug
21-3
1 A
ug
1-10
Sep
t
11-2
0 S
ept
21-3
0 S
ept
1-10
Oct
11-2
0 O
ct
21-3
1 O
ct
1-10
Nov
11-2
0 N
ov
21-3
0 N
ov
1-10
Dec
11-2
0 D
ec
21-3
1 D
ec
1-10
Jan
Date
Freq
uenc
y of
TC
s w
ith P
REs
0
10
20
30
40
50
60
70
80
TC F
requ
ency
TCs with PREsTCs
CLIMATOLOGY
Frequency Comparison of TC Occurrence with TCs Producing PREs 1979-2005
0
2
4
6
8
10
12
14
16
18
20
PRE Left of TC Track PRE Along TC Track PRE Right of TC Track
Relative Locations
Freq
uenc
y
CLIMATOLOGY
TC Track vs. PRE Location 32 Cases 2004-2005
• Composition of Data Catalog- PRE 3 h positions based on rainfall centroid - TC positions and intensities during PREs - Approximate rainfall amounts isolated for each PRE
• Major PRE Characteristics- 12 TCs produced 32 PREs in 2004 and 2005
- Median Separation Distance: 987 km - Median Time Lag: 30 h - Median Event Duration: 12 h - Slow-moving TCs more likely to produce multiple PREs compared to those moving more quickly
CLIMATOLOGY
Heavy rainfall developed in association with:
• Mid- and upper-level jet-entrance region confluence zone
• Differential CVA caused by a weak short wave
• Moisture tongue extending through low-level ridge line
Bosart and Carr (1978) conceptual model of antecedent rainfall
PAST RESEARCH ON PRE WITH AGNES (1972)
CASE STUDY: KATRINA (29-30 AUG 2005)
1200 UTC 050829 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
1200 UTC 050829 200 hPa Ht (dam) and Winds (kts) 1200 UTC 050829 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
1200 UTC 050829 WSI NOWRAD 2 KM US Radar Mosaic
1800 UTC 050829 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
1800 UTC 050829 200 hPa Ht (dam) and Winds (kts) 1800 UTC 050829 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
1800 UTC 050829 WSI NOWRAD 2 KM US Radar Mosaic
0000 UTC 050830 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
0000 UTC 050830 200 hPa Ht (dam) and Winds (kts) 0000 UTC 050830 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
0000 UTC 050830 WSI NOWRAD 2 KM US Radar Mosaic
0600 UTC 050830 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
0600 UTC 050830 200 hPa Ht (dam) and Winds (kts) 0600 UTC 050830 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
0600 UTC 050830 WSI NOWRAD 2 KM US Radar Mosaic
1200 UTC 050830 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
1200 UTC 050830 200 hPa Ht (dam) and Winds (kts) 1200 UTC 050830 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
1200 UTC 050830 WSI NOWRAD 2 KM US Radar Mosaic
1800 UTC 050830 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
1800 UTC 050830 200 hPa Ht (dam) and Winds (kts) 1800 UTC 050830 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
1800 UTC 050830 WSI NOWRAD 2 KM US Radar Mosaic
NULL CASE: CINDY
6-7 July 2005
1200 UTC 050706 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
1200 UTC 050706 200 hPa Ht (dam) and Winds (kts) 1200 UTC 050706 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
1200 UTC 050706 WSI NOWRAD 2 KM US Radar Mosaic
1800 UTC 050706 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
1800 UTC 050706 200 hPa Ht (dam) and Winds (kts) 1800 UTC 050706 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
1800 UTC 050706 WSI NOWRAD 2 KM US Radar Mosaic
0000 UTC 050707 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
0000 UTC 050707 200 hPa Ht (dam) and Winds (kts) 0000 UTC 050707 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
0000 UTC 050707 WSI NOWRAD 2 KM US Radar Mosaic
0600 UTC 050707 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
0600 UTC 050707 200 hPa Ht (dam) and Winds (kts) 0600 UTC 050707 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
0600 UTC 050707 WSI NOWRAD 2 KM US Radar Mosaic
1200 UTC 050707 925 hPa Ht (dam), Theta-e (K), and Winds (kts)
1200 UTC 050707 200 hPa Ht (dam) and Winds (kts) 1200 UTC 050707 700 hPa Ht (dam), AVor (10-5 s-1), and 1000-500 hPa Thck (dam)
1200 UTC 050707 WSI NOWRAD 2 KM US Radar Mosaic
CONCLUSIONS• Katrina vs. Cindy Comparison
- Bosart and Carr (1978) schematic model, coupled with separation distance, time lag, and TC speed statistics, may aid in predicting if, where, and how many PREs will develop
- Longitude and orientation of trough axes appear important in determining potential PRE development
• Katrina Case Study- Weak forcing for ascent may be sufficient to trigger coherent areas of heavy rain downstream of approaching TCs
- Positive θe advection and divergent jet entrance and exit regions promote favorable conditions for heavy rain formation
• Expand PRE climatological data further back in time
• Provide adequate physical explanations for the differences between left-of-track, along-track, and right-of-track PREs, and the apparent left-of-track preference
• Examine the role mesoscale features may have played in the development of recent PREs
• Classify and subdivide the different modes of predecessor rain events
FUTURE RESEARCH