Mesoscale Precipitation Structures Accompanying Landfalling and

Transitioning Tropical Cyclones in the Northeast United States

Jared Klein, Lance F. Bosart, and Daniel KeyserUniversity at Albany, SUNY, Albany, NY

CSTAR II Grant NA04NWS4680005

David ValleeNWS Weather Forecast Office, Taunton, MA

M.S. Thesis Seminar5 July 2007

Objectives

• Examine the distribution of rainfall in relation to tropical cyclone (TC) track and identify smaller-scale areas of enhanced rainfall accompanying landfalling and transitioning TCs in the Northeast U.S.

• Identify key synoptic- and mesoscale processes that impact the precipitation distribution for these TCs.– Upstream thermal trough and downstream thermal

ridge–jet interactions– Upper-level jet (ULJ) and lower-level jet (LLJ)

interactions– TC-induced coastal frontogenesis– Orographic precipitation enhancement

Motivation

• Timing and location of mesoscale features is difficult to predict.

• Inland flooding is responsible for nearly 60% of fatalities from landfalling TCs (Rappaport 2000).

• There has been a recent increase in frequency of TC-related flooding events over the Northeast.– 1950–2003: Average of 1 event every year– 2004–2005: 10 events in 2 years

NPVU QPE

Total precip (in.) vs. TC track: 2004-2005 Total Precip (in.)–10 Storms

Max Rainfall: Max Rainfall:

35 in.35 in.

Data and Methodology

• Identify TCs that produced ≥ 100 mm (4 in.) of rainfall in the Northeast U.S. for 1950–2006.

1950 Able1950 Dog1952 Able1953 Barbara1953 Carol1954 Carol1954 Edna1954 Hazel1955 Connie1955 Diane1955 Ione1958 Helene1959 Cindy

1959 Gracie1960 Brenda1960 Donna1961 Esther1962 Alma1962 Daisy1963 Ginny1969 Gerda1971 Doria1971 Heidi1972 Agnes1972 Carrie 1976 Belle

1979 David1985 Gloria1988 Chris1991 Bob1996 Bertha1996 Edouard1996 Fran1997 Danny1998 Bonnie1999 Floyd2001 Allison2002 Isidore2002 Kyle

2003 Bill2003 Isabel2004 Alex2004 Bonnie2004 Charley2004 Frances2004 Gaston2004 Ivan2004 Jeanne2005 Cindy2005 Katrina2005 Ophelia2006 Ernesto

• Construct a climatology of precipitation distribution vs. TC track.– 2.5° NCEP–NCAR reanalysis for synoptic diagnostics– 0.25° NCEP 24 h daily (1200–1200 UTC) UPD– Higher resolution precipitation analysis produced by Ron

Horwood (NERFC)– 10 km RFC NPVU archived QPE– NHC best-track data

• Diagnose synoptic- and mesoscale processes associated with heavy precipitation for Ivan (2004) and Ernesto (2006).– Upper-air analyses and Q vector (geostrophic wind) diagnostics

using 1.0° GFS dataset– Surface analyses and F vector (full wind) diagnostics using ~0.6°

dataset created from GEMPAK

Data and Methodology

Climatology Results

LOT = left of trackROT = right of track

0

5

10

15

20

25

30

35

Number of TCs

LOT ROT Distinct ROT toLOT Shift

Distinct LOT toROT Shift

No PreferredDistribution

Jun–Oct Climatology of Precipitation Distribution vs. TC Track: 1950–2006

Jun Jul Aug Sep Oct

34

3

5

1

9

• Upper-level downstream ridge and jet development.– Occurred in nearly every case– Placed Northeast U.S. in equatorward jet-entrance region– Amplified LLJ and positive θe advection

• Enhanced precipitation as TC interacts with a pre-existing mesoscale boundary or coastal front.– Occurred in almost every case– Heavy precipitation region along and in cold sector of

coastal front (CF)– Stronger θ gradient when interacting with a upstream

midlatitude trough during extratropical transition (ET)

Climatology Results

• Possible orographic enhancement of precipitation.– Occurred in almost half the cases– Track far enough inland so that low-level easterly flow

ahead of storm was upslope on the eastern sides of the Appalachian Mountains

Climatology Results

Preferred Areas of Possible Orographic Precipitation Enhancement in the Northeast U.S.

http://fermi.jhuaple.edu/states.htmlBlue RidgeBlue Ridge

CatskillsCatskills

BerkshiresBerkshires

WhiteWhite

Q vector: Time rate of change ofQ div–con: QG forcing for descent– ascent

Qs: Time rate of change of direction ofQs div–con: QG forcing for descent–ascent within thermal trough–ridge

Qn: Time rate of change of magnitude of Qn div–con: QG forcing for descent–ascent on cold–warm side of frontal zone

θΔθΔAdapted from Martin (1999)

Q Vector Partitioning in Natural Coordinates

θΔ

Case Study 1:

Ivan

September 2004

LOT PrecipDistribution

NPVU QPE

09/1709/17

09/1909/1909/1809/18

Dates denoteDates denote0000 UTC positions0000 UTC positions

Total precip (in.) vs. TC track: 1200 UTC 16 Sep–1200 UTC 19 Sep 2004

Ivan

Case Study 1: Ivan

300 hPa h (dam), wind speed (m s−1), and div (10−5 s−1)

300 hPa Analyses: 1200 UTC 16 September 2004

300 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

1.0° GFS

Confluent flow in equatorward jet-entrance region

300 hPa Analyses: 1200 UTC 17 September 2004

300 hPa h (dam), wind speed (m s−1), and div (10−5 s−1)

300 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

1.0° GFS

Frontogenesis in jet-entrance region

300 hPa Analyses: 1200 UTC 18 September 2004

Strengthening downstream ULJ and ridge

300 hPa h (dam), wind speed (m s−1), and div (10−5 s−1)

300 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

1.0° GFS

Strong frontogenesis in jet-entrance region

925 hPa Analyses: 1200 UTC 16 September 2004

925 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

WSI radar, 925 hPa θe (K) and wind barbs (kt)

Pre-existing baroclinic zoneSymmetric reflectivity structure

1.0° GFS

925 hPa Analyses: 1200 UTC 17 September 2004

925 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

WSI radar, 925 hPa θe (K) and wind barbs (kt)

Northeastward extension of precip field along baroclinic zone

1.0° GFS

Band of frontogenesis along baroclinic zone

925 hPa Analyses: 1200 UTC 18 September 2004

925 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

WSI radar, 925 hPa θe (K) and wind barbs (kt)

Highest reflectivity near nose of LLJ/θe ridge axis

1.0° GFS

Strong frontogenesis along warm frontal zone

925 hPa Q Vector Diagnosis: 0000 UTC 18 September 2004

Radar at 1200 UTC 17 September 2004

Q Qn

QsRadar at 0000 UTC 18 September 2004

Highest reflectivity near strongest QG forcing for ascent

Radar at 0000 UTC 18 September 2004

WSI radar

Qs div–con couplet within thermal trough–ridge

Q vectors (10−10 K m−1 s−1 beginning at 2.5 × 10−11), θ (K) contoured in green, and Q div–con (10−15 K m−2 s−1) shaded in cool–warm colors

Qn div–con bands within frontal zone

1.0° GFS

Radar at 1200 UTC 17 September 2004

Q Qn

QsRadar at 0000 UTC 18 September 2004

Highest reflectivity near strongest QG forcing for ascent

Radar at 0600 UTC 18 September 2004

WSI radar

925 hPa Q Vector Diagnosis: 0600 UTC 18 September 2004

Q vectors (10−10 K m−1 s−1 beginning at 2.5 × 10−11), θ (K) contoured in green, and Q div–con (10−15 K m−2 s−1) shaded in cool–warm colors

1.0° GFS

Radar at 1200 UTC 17 September 2004Radar at 0000 UTC 18 September 2004Radar at 1200 UTC 18 September 2004

Q Qn

Qs

WSI radar

925 hPa Q Vector Diagnosis: 1200 UTC 18 September 2004

Q vectors (10−10 K m−1 s−1 beginning at 2.5 × 10−11), θ (K) contoured in green, and Q div–con (10−15 K m−2 s−1) shaded in cool–warm colors

1.0° GFS

Highest reflectivity near strongest QG forcing for ascent

Cross Section of Fn Magnitude: 0000 UTC 18 September 2004

Deep frontogenesis tilting toward cold air w/height

925–500 hPa layer-avg Fn vectors (10−10 K m−1 s−1),θ (K) contoured in green, and Fn div–con (10−15 K m−2 s−1) shaded in cool–warm colors

Fn magnitude [K (100 km)−1 (3 h)−1] shaded, θ (K) contoured in gray, wind barbs (m s−1), and ω<0 (µb s−1) contoured in red1.0°

GFS

Cross Section of Fn Magnitude: 1200 UTC 18 September 2004

Deep frontogenesis tilting toward cold air w/height

925–500 hPa layer-avg Fn vectors (10−10 K m−1 s−1),θ (K) contoured in green, and Fn div–con (10−15 K m−2 s−1) shaded in cool–warm colors

Fn magnitude [K (100 km)−1 (3 h)−1] shaded, θ (K) contoured in gray, wind barbs (m s−1), and ω<0 (µb s−1) contoured in red1.0°

GFS

Heaviest 6-h precip along and on cold side of surface boundary

6-h precipitation (in) ending at 0600 UTC 18 September 2004

0000 UTC 18 September 2004

NPVU QPE

Flow of tropical air into surface boundary

Fn vectors (10−10 K m−1 s−1 beginning at 1.0 × 10−10), θ (K) contoured in green, streamlines contoured in black, and Fn div–con (10−14 K m−2 s−1) shaded in cool–warm colors

~0.6° surface data

0600 UTC 18 September 2004

Heaviest 6-h precip along and on cold side of surface boundary

6-h precipitation (in) ending at 1200 UTC 18 September 2004

0600 UTC 18 September 2004

NPVU QPE

Flow of tropical air into surface boundary

Fn vectors (10−10 K m−1 s−1 beginning at 1.0 × 10−10), θ (K) contoured in green, streamlines contoured in black, and Fn div–con (10−14 K m−2 s−1) shaded in cool–warm colors

~0.6° surface data

1200 UTC 18 September 2004

Case Study 2:

Ernesto

August–September 2006

ROT PrecipDistribution

NPVU QPE

Dates denoteDates denote0000 UTC positions0000 UTC positions

09/0109/01

09/0209/02

09/0309/03

Total precip (in.) vs. TC track: 1200 UTC 31 Aug–1200 UTC 1 Sep 2006

Case Study 2: Ernesto

300 hPa h (dam), wind speed (m s−1), and div (10−5 s−1)

300 hPa Analyses: 1200 UTC 31 August 2006

300 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

Jet much farther downstream than with Ivan

1.0° GFS

300 hPa h (dam), wind speed (m s−1), and div (10−5 s−1)

300 hPa Analyses: 1200 UTC 1 September 2006

300 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

1.0° GFS

925 hPa Analyses: 1200 UTC 31 August 2006

925 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

WSI radar, 925 hPa θe (K) and wind barbs (kt)

1.0° GFS

925 hPa Analyses: 1200 UTC 1 September 2006

925 hPa frontogenesis [K (100 km)−1 (3 h)−1], θ (K), and wind barbs (kt)

WSI radar, 925 hPa θe (K) and wind barbs (kt)

Highest reflectivity near nose of LLJ/θe ridge axis

Strong frontogenesis along warm frontal zone

1.0° GFS

Radar at 0000 UTC 1 September 2006

Qn div–con bands within coastal boundary as Ernesto nears landfall

Strong forcing for descent–ascent associated with Qn and Qs div–con

925 hPa Q Vector Diagnosis: 0000 UTC 1 September 2006

Q Qn

Qs

WSI radar

Q vectors (10−10 K m−1 s−1 beginning at 2.5 × 10−11), θ (K) contoured in green, and Q div–con (10−15 K m−2 s−1) shaded in cool–warm colors

1.0° GFS

Radar at 0600 UTC 1 September 2006

925 hPa Q Vector Diagnosis: 0600 UTC 1 September 2006

Q Qn

Qs

WSI radar

Highest reflectivity near strongest QG forcing for ascent

Q vectors (10−10 K m−1 s−1 beginning at 2.5 × 10−11), θ (K) contoured in green, and Q div–con (10−15 K m−2 s−1) shaded in cool–warm colors

1.0° GFS

Radar at 1200 UTC 1 September 2006

925 hPa Q Vector Diagnosis: 1200 UTC 1 September 2006

Q Qn

Qs

WSI radar

Highest reflectivity near strongest QG forcing for ascent

Q vectors (10−10 K m−1 s−1 beginning at 2.5 × 10−11), θ (K) contoured in green, and Q div–con (10−15 K m−2 s−1) shaded in cool–warm colors

1.0° GFS

Cross Section of Fn Magnitude: 0000 UTC 1 September 2006

925–500 hPa layer-avg Fn vectors (10−10 K m−1 s−1),θ (K) contoured in green, and Fn div–con (10−15 K m−2 s−1) shaded in cool–warm colors

Fn magnitude [K (100 km)−1 (3 h)−1] shaded, θ (K) contoured in gray, wind barbs (m s−1), and ω<0 (µb s−1) contoured in red

Strongest frontogenesis focused near surface

1.0° GFS

Cross Section of Fn Magnitude: 1200 UTC 1 September 2006

925–500 hPa layer-avg Fn vectors (10−10 K m−1 s−1),θ (K) contoured in green, and Fn div–con (10−15 K m−2 s−1) shaded in cool–warm colors

Fn magnitude [K (100 km)−1 (3 h)−1] shaded, θ (K) contoured in gray, wind barbs (m s−1), and ω<0 (µb s−1) contoured in red

Strongest frontogenesis focused near surface

1.0° GFS

Heaviest 6-h precip along and on cold side of surface boundary

6-h precipitation (in) ending at 1200 UTC 1 September 2006

0600 UTC 1 September 2006

NPVU QPE

Fn vectors (10−10 K m−1 s−1 beginning at 1.0 × 10−10), θ (K) contoured in green, streamlines contoured in black, and Fn div–con (10−14 K m−2 s−1) shaded in cool–warm colors

1200 UTC 1 September 2006

~0.6° surface data

Heaviest 6-h precip along and on cold side of surface boundary

6-h precipitation (in) ending at 1800 UTC 1 September 2006

1200 UTC 1 September 2006

NPVU QPE

Fn vectors (10−10 K m−1 s−1 beginning at 1.0 × 10−10), θ (K) contoured in green, streamlines contoured in black, and Fn div–con (10−14 K m−2 s−1) shaded in cool–warm colors

1800 UTC 1 September 2006

~0.6° surface data

Upper-level

Upper-level

jet streak

jet streak

low-level Qn

LLJLLJ

QQss div div

QQ nn div div

QQss con con

QQ nn con con

low-level θ

Summary of Case Studies: Conceptual Model 1

Heavy

Heavy

ra

infa

ll

rain

fall

sfc boundary

LOTLOTPrecipitation DistributionPrecipitation Distribution

ROTROTPrecipitation DistributionPrecipitation Distribution

ColdCold WarmWarm

ZZ

θθColdCold WarmWarm

ZZ

θθ

Strongest frontogenesis focused near surface

Deep frontogenesis tilting toward cold air w/height

Summary of Case Studies: Conceptual Model 2

Acknowledgements

• Special thanks to:– Lance Bosart and Dan Keyser– David Vallee– John Cannon and Dan St. Jean - WFO

GYX– Kevin Tyle and Alan Srock– The rest of the grad students for

keeping me sane for the past two years!

– My family– Adrienne

Summary of Case Studies

• Heaviest precipitation occurs in the presence of strong surface F vector convergence and upper-air Q vector convergence.– Qn forcing for descent–ascent bands located within low-

level frontal zone beneath equatorward jet-entrance region

– Qs forcing for descent–ascent couplet located within upstream–downstream thermal trough–ridge over eastern U.S.

• Heaviest 6-h precipitation occurs along and on cold side of mesoscale surface boundary.

• Both environmental circulation of TC and downstream LLJ induce the poleward transport of high θe air into a pre-existing low-level baroclinic zone.

• LOT and ROT precipitation distribution is related to vertical structure of frontogenesis.– Ivan: LOT precipitation distribution with deep

frontogenesis tilting toward cold air with height– Ernesto: ROT precipitation distribution with strongest

frontogenesis focused near the surface

Summary of Case Studies

• Introduction– Objectives– Motivation

• Data and Methodology

• Results– Climatology– Case Studies

• Conceptual Models

Outline