Synoptic environments associated with predecessor rain events in advance of

landfalling tropical cyclones

Benjamin J. Moore, Lance F. Bosart, and Daniel KeyserDepartment of Atmospheric and Environmental Sciences, University at

Albany/SUNY, Albany, NY 12222

Michael L. Jurewicz, Sr.NOAA/NWS, Binghamton, NY

Northeast Regional Operational Workshop XI, Albany, NY

5 Nov 2009

NOAA/CSTAR Grant NA07NWS4680001

Outline

• Motivation• Definition of a PRE• Data and methodology• TC-relative composite analysis• PREs associated with TC Frances (2004) and TC

Rita (2005)• Concluding remarks

Motivation

• Identify preferential dynamic and thermodynamic configurations for PREs to improve forecasts

• Establish physical mechanisms accounting for different spatial and temporal characteristics of PREs

TC Frances12Z 8 Sep 2004

TC Rita06Z 25 Sep 2005

66 66PRE

PRE

Motivation

Definition of a PRE

• Defined as distinct mesoscale regions of heavy rainfall [~100 mm (24 h)−1] ~1000 km downstream of landfalling and recurving TCs (Cote 2007)

• Develop as a poleward stream of deep moisture from the TC interacts with a baroclinic environment

Conceptual model from Bosart and Carr (1978) for a rain event associated with TC Agnes (1972)

Data and Methodology

• PREs for 1988–2008 identified using:• National base reflectivity radar mosaics (cases during

1995–2008)• 1° GFS analyses and 2.5° NCEP–NCAR reanalysis data • NCDC Hourly Precipitation Dataset• NPVU QPE • UPD

• PREs stratified by TC recurvature at time of PRE initiation

• Pre-recurvature – no component of TC motion vector in the positive x-direction• Post-recurvature – component of TC motion vector in

the positive x-direction

Data and Methodology

• TC-relative compositing:– 6 hourly 2.5° NCEP–NCAR grids for PRE cases were

shifted so that TCs were located at same position– PRE cases were stratified into pre- and post-

recurvature categories and composited at time of initiation

– Cases which deviated significantly in synoptic environment were excluded

– Only one PRE from each parent TC was used in compositing

PREs 1988−2008

PRE-REC

URVATURE

POST-RECURVATURE

05

10152025303540

Num

ber o

f PRE

s

PRE-REC

URVATURE

POST-REC

URVATURE0

5

10

15

20

25

DURA

TIO

N (h

)

• 65 PREs associated with 37 TCs• Pre-recurvature category is

characterized by larger separation distance and longer duration

PRE-RECURVATURE POST-RECURVATURE300

500

700

900

1100

1300

1500

SEPA

RATI

ON

DIS

TAN

CE (k

m)

29

34

N=63

TC-Relative Composites

Pre-recurvature PREs Post-recurvature PREsN=12 N=13

kts

200 hPa heights (dam, black), winds (kts, barbs ≥40 kts), wind speed (kts, shaded ≥50 kts); 850 hPa relative vorticity (10−5 s−1, blue)

200 hPa

TC-Relative Composites

Pre-recurvature PREs Post-recurvature PREsN=12 N=13

mm

700 hPa heights (dam, black), 500-850 hPa layer-averaged wind (kts, barbs ≥10kts), total column precipitable water (mm, shaded)

700 hPa

TC-Relative Composites

Pre-recurvature PREs Post-recurvature PREsN=12 N=13

850 hPa heights (dam, black), Q-vectors (10 −11 K m −1 s −1), Q-vector convergence (10 −16 K m −2 s−1, shaded), potential temperature (K, red)

850 hPa

10 −16 K m −2 s −1

PRE associated with TC Rita 24–26 Sep 2005Pre-recurvature PRE

1200 UTC 24 Sep – 0000 UTC 26 Sep 2005: 200 hPa mean geopotential height (dam, black), wind speed (≥70 kts, red), and total precipitation (mm, shaded)

mm

00Z25 Sep

06Z19 Aug

03Z25 Sep

06Z25 Sep

12Z25 Sep

Source: NCAR case selection archive

Radar EvolutionWSR-88D base reflectivity

Synoptic Environment

mm850 hPa heights (dam, black),

Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)

kts

200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);

850 hPa relative vorticity (10−5 s−1, blue)

0600 UTC 25 Sep 2005

850 hPa 200 hPa

Synoptic Environment

mm850 hPa heights (dam, black),

Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)

kts

200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);

850 hPa relative vorticity (10−5 s−1, blue)

0600 UTC 25 Sep 2005

850 hPa Pre-recurvature composite

Synoptic Environment

mm850 hPa heights (dam, black),

Q-vectors (10−11 K m−2 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)

kts

200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);

850 hPa relative vorticity (10−5 s−1, blue)

0600 UTC 25 Sep 2005

200 hPaPre-recurvature composite

1200 UTC 7 Sep – 0000 UTC 9 Sep 2004: 200 hPa mean geopotential height (dam, black), wind speed (≥70 kts, red), and total precipitation (mm, shaded)

mm

PRE associated with TC Frances 7–8 Sep 2004Post-recurvature PRE

Radar Evolution

06Z8 Sep

12Z08 Sep

09Z8 Sep

15Z8 Sep

Source: NCAR case selection archive

WSR-88D base reflectivity

Synoptic Environment

mm850 hPa heights (dam, black),

Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)

kts

200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);

850 hPa relative vorticity (10−5 s−1, blue)

1200 UTC 8 Sep 2004

850 hPa 200 hPa

Synoptic Environment

mm850 hPa heights (dam, black),

Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)

kts

200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);

850 hPa relative vorticity (10−5 s−1, blue)

1200 UTC 8 Sep 2004

Post-recurvature composite850 hPa

Synoptic Environment

mm850 hPa heights (dam, black),

Q-vectors (10−11 K m−2 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)

kts

200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);

850 hPa relative vorticity (10−5 s−1, blue)

1200 UTC 8 Sep 2004

Post-recurvature composite 200 hPa

PREs in context of extreme rain producing MCSs

Frontal type flash flood pattern from Maddox et al. (1979)

PRE Composite

Surface 1000 hPa winds (m s−1), heights (dam), θe (K)

66

LH

5 m s−1

Concluding RemarksKey features of composites– Pre-recurature PREs• PRE develops in equatorward entrance region of

anticyclonically curved upper-level jet streak

• Upper-level flow characterized by ridge overlying the TC and broad, positively tilted trough well upstream and poleward of TC

• Low-level anticyclone downstream of TC facilitates poleward flow towards zonally oriented baroclinic zone frontogenetical forcing, moisture transport from the TC

Concluding RemarksKey features of composites– Post-recurvature• PRE develops in equatorward entrance region of

anticyclonically curved upper-level jet streak

• TC much closer to axis of upstream trough and jet streak

• TC circulation impinges upon low-level baroclinic zone

• Frontogenetical forcing at the terminus of low-level jet associated with TC circulation and downstream anticyclone

• Tropical moisture plume extends poleward and eastward along a SW−NE oriented baroclinic zone

Case studies– Rita (2005): Pre-recurvature PRE

• PRE was quasi-stationary and long-lived• PRE developed along zonal baroclinic zone in equatorward

entrance region of upper-level jet• Anticyclone over the eastern U.S. aided in the transport of TC

moisture to region of lift– Frances (2004): Post-recurvature PRE

• PRE was small-scale and quasi-stationary• PRE developed on the warm side of baroclinic zone in

equatorward entrance region of upper-level• Strong low-level flow associated with TC and downstream ridge

was associated with moisture transport and warm air advection

Concluding Remarks