Title: Predecessor Rainfall Events (PRE) in Tropical Cyclones - Results from a Recent Northeastern U.S. Collaborative Science, Technology, and Research (CSTAR) Project
1Predecessor Rainfall Events (PRE) in Tropical
Cyclones - Results from a Recent Northeastern
U.S. Collaborative Science, Technology, and
Research (CSTAR) Project
- Matthew Cote, Lance Bosart, and Daniel Keyser
- State University of New York, Albany, NY
- Michael L. Jurewicz, Sr.
- National Weather Service, Binghamton, NY
- July 10, 2008 HPC, Camp Springs, MD
2Outline
- Data Sources
- Definition of PRE
- Motivating factors / goals for this session
- Methodologies for the project
- Categorize PRE / Establish climatologies for the
Eastern U.S. / Atlantic Basin TC - Provide operational forecasting resources
- Composites / Conceptual models
- Case Study Examples
- Summary
3Data Sources
- WSI NOWRAD Radar Imagery
- HPC Surface / Radar Analyses
- SPC Upper-Air / Mesoanalyses
- Archived TC Tracks / Positions from TPC
- NARR 32-km Datasets
- NWS WES Imagery
- NPVU QPE Data from NWS RFCs
4PRE What are They ?
- Coherent areas of heavy rainfall observed
poleward of Tropical Cyclones (TC) - Distinct from the main precipitation shields of
TC, or their extra-tropical remnants - Yet, still indirectly tied to TC
5PRE Example Frances (2004)
Main Precipitation Shield of the TC
PRE
6Results of the Frances PRE
7Motivation for Research
- PRE can be particularly challenging phenomena for
operational meteorologists - NWP models often underestimate / misplace heavy
rainfall associated with PRE - Poor handling of diabatic heating transfer /
upper-jet intensification - Attention is frequently diverted to different
areas / times - Closer to where TC make landfall
- Future time periods when the more direct impacts
of TC or their remnants may be expected
8Goals
- To provide NWS forecasters / operational
meteorologists with - Background Knowledge / Awareness of PRE
- Forecast Tools
- PRE Climatologies
- Conceptual Models / Composite Charts
- Case Study Examples
9Methodology
- We restricted classifications of PRE to systems
that met the following criteria - 100 mm (4) of rainfall needed to be observed
within a 24-hour period - Such rainfall had to be connected with a well
defined region of precipitation - Not scattered / isolated convection
10Frequency of Occurrence
- Our period of study ran from 1998 to 2006
- 47 PRE were identified, which were tied to a
total of 21 TC - An average of about 2 PRE per PRE-producing TC
(PPTC) - About 1/3 of all Atlantic Basin TC that made U.S.
Landfall for this period were PPTC - A few outlier PPTC did not actually make landfall
11PRE Statistics
Agnes PRE
Separation Distance 1086 482 km
Median 935 km
Bosart and Carr (1978) conceptual model of
antecedent rainfall indirectly associated with TC
Agnes (from 1972)
12PRE Statistics (Continued)
Agnes PRE
Separation Distance 1086 482 km
Median 935 km Event Duration 14 7 h
Median 12 h
Bosart and Carr (1978) conceptual model of
antecedent rainfall indirectly associated with TC
Agnes (from 1972)
13PRE Statistics (Continued)
AT
ROT
Separation Distance 1086 482 km
Median 935 km Event Duration 14 7 h
Median 12 h Time
Lag 45 29 h Median 36 h
LOT
Bosart and Carr (1978) conceptual model of
antecedent rainfall indirectly associated with TC
Agnes (from 1972)
14PRE Track-Relative Positions
26
12
9
15PRE Track-Relative Positions
Potential for excessive flooding beginning before
arrival of TC rainfall
26
12
9
16PRE Track-Relative Positions
Potential for flooding in areas not directly
impacted by TC rainfall
26
12
9
17Further Sub-Classifications
- Separation by Similarity of TC Track
- Southeast Recurvatures (SR)
- Highest percentage of PPTC
- Atlantic Recurvatures (AR)
- Most common TC Track
- Central Gulf Landfalls (CG)
- Lower percentage of PPTC, but high frequency PRE
production within those PPTC - Other Hybrid TC that were harder to categorize
18SR TC Tracks and PRE Locations
All SR PPTC Tracks with PRE centroids (colored
dots)
All SR TC Tracks
19AR TC Tracks and PRE Locations
All AR PPTC Tracks with PRE centroids (colored
dots)
All AR TC Tracks
20CG TC Tracks and PRE Locations
All CG PPTC Tracks with PRE centroids (colored
dots)
All CG Tracks
21Favorable Locations for PRE
- Within the Right-rear quadrant (RRQ) of an
Upper-level Jet - Ahead of the Mean Long-Wave Trough Axis at
Mid-levels (trough axis is west of the parent
TCs longitude) - Near or just upstream from Short-wave Ridging
- Near a Low-level Front / Baroclinic Zone
- On the periphery of a Tropical Moisture Plume
- Near or just west of a Low-level Theta-E Ridge
Axis
22SR PPTC Composites (PRE - 12)
Trough axis
Ridge axis
?e-Ridge axis
700 mb heights (dam) and upward
vertical motion (shaded, µb s-1)
925 mb heights (dam), ?e (K), and
200 mb winds (shaded, m s-1)
Center of composite TC
23SR PPTC Composites (At Time of PRE)
Trough axis
Ridge axis
?e-Ridge axis
700 mb heights (dam) and upward vertical motion
(shaded, µb s-1)
925 mb heights (dam), ?e (K), and
200 mb winds (shaded, m s-1)
Center of composite TC
Centroid of 1st composite PRE
24SR PPTC Composites (PRE 12)
Ridge axis
Trough axis
?e-Ridge axis
700 mb heights (dam) and upward
vertical motion (shaded, µb s-1)
925 mb heights (dam), ?e (K), and
200 mb winds (shaded, m s-1)
Center of composite TC
Centroid of 1st composite PRE
Centroid of 2nd composite PRE
25Common Detracting Elements for PRE Formation
- A Zonal Flow Pattern is in place Poleward of the
TC - Lack of merdional flow discourages northward
return of deep tropical moisture away from the TC
itself - The Long-wave Mid-level Trough Axis is already
east of the TCs Longitude - A Low-level Blocking Ridge is located north /
northeast of the TC - Tends to prevent significant moisture inflow into
any frontal boundaries or jet circulations that
may be poleward of the TC
26SR Null-Case Composites
700 mb heights (dam) and upward vertical motion
(shaded, µb s-1)
925 mb heights (dam), ?e (K), and
200 mb winds (shaded, m s-1)
Center of composite TC
27Case Study (TC Erin, 2007)
- CG Landfall PPTC
- Several PRE were associated with Erin (typical of
CG PPTC) - Erins PRE exhibited many of the classic
synoptic-scale ingredients - Within RRQ of an upper-level jet
- Deep moisture was fed northward into the PRE /
pronounced theta-e ridging developed - A low-level boundary was in the vicinity
28Track of Erin (Aug. 15-20, 2007)
20/00z
19/12z
19/06z
19/00z
18/12z
29Multiple PRE Producer (First 2 PRE)
PRE 2 4-8 (100-200 mm) of rain early on
8/18/07
PRE 1 3-6 (75-150 mm) of rain late on 8/17/07
(Along-track PRE)
30Erins 3rd PRE
Locally 10
Locally 12 (300 mm) of rain on the evening of
8/18/07
31Ramifications of PRE 3
- 12 - 15 of rain fell in 6 hours or less over
parts of Southeastern MN and Southwestern WI - Record flooding
- Several fatalities
32Water Vapor 02z, 8/19/07
Significant PRE
Erins Moisture Plume
L
TD Erin
MSLP Isobars and Mean 925-850 mb Winds
33300 mb Analysis 00z, 8/19/07
PRE
Jet Entrance Region
34850 mb Moisture Transport - 00z, 8/19/07
PRE
L
TD Erin
35Surface Analysis Radar - 00z, 8/19/07
PRE
36Flooding Pictures
37Null-Case Study (TC Gabrielle, 2007)
- Became a Tropical Storm over the western
Atlantic, before brushing the Outer Banks of NC - Then recurved towards the east-northeast over the
open Atlantic (Would be categorized as an AR TC) - No PRE were associated with this TC
- Expansive ridge axis blocked advection of deeper
moisture into the U.S.
38Track of Gabrielle (Sept. 8-12, 2007)
3924 Hour QPE Ending 12z, Sept. 10, 2007
Localized 1-2 (25-50 mm) rainfall amounts in a
24 hour period Available moisture was not
associated with Gabrielle
40Water Vapor 09z, 9/09/07
Frontal Plume of MoistureDisconnected from
Gabrielle
Dry Wedge
Gabrielle
MSLP Isobars and Mean 925-850 mb Winds
41300 mb Analysis 12z, 9/09/07
Trough Axis
Ridge Axis
L
Gabrielle
42850 mb Moisture Transport 12z, 9/09/07
Axis of minimum Theta-e
L
Gabrielle
43Surface Analysis Radar - 12z, 9/09/07
Ridge axis blocks inflow of moisture towards
poleward front
44Conceptual Model LOT PRE (SR/AR TC)
UL Jet
LL ?e-Ridge Axis
PREs
See inset
ML Streamlines
TC Rainfall
Revised and updated from Fig. 13 of Bosart and
Carr (1978)
Representative TC Tracks
45Conceptual Model (More Detailed Inset)
UL Jet
LL ?e-Ridge Axis
Mountain Axes
LL Temp/ Moisture Boundary
UL Jet
LL ?e-Ridge Axis
PREs
PREs
Idealized LL Winds
ML Streamlines
TC Rainfall
TC Tracks
46Summary Forecast Challenges
- NWP models are often poor with the placement /
intensity of PRE - Attention is frequently diverted away from
potential PRE development - PRE can impact almost any area of the CONUS
47Summary PRE Statistics
- About 1/3 of U.S. Landfalling TC in our period of
study (1998-2006) were PPTC - LOT PRE were the most common
- Typically the best synoptic enhancement
- AT PRE can be the most dangerous
- Double-shot of heavy rainfall
- ROT PRE tended to display the highest rainfall
rates - Typically slower moving PRE, with less synoptic
forcing - Orography perhaps more important
48Summary Similarity of TC Tracks
- SR TC had the highest percentage of PPTC
- AR TC were the most common in our period of study
- However, had a lower percentage of PPTC
- CG TC had the lowest percentage of PPTC
- However, CG PPTC were the most prolific PRE
producers (an average of 3-4 PRE per TC)
49Summary Favored PRE Locations
- Within the RRQ of a strengthening poleward
upper-level jet streak - Downstream of a mid-level trough, which is well
west of the parent TCs longitude - Near a low-level boundary
- On the northern or western fringes of a deep
tropical moisture plume (evident on water vapor
imagery) - Near or just west of a low-level theta-e ridge
axis
50Summary Unfavorable Setup for PRE
- A de-amplified, zonally oriented flow pattern is
in place north of the TC - The main poleward mid-level trough axis is
already at, or east of the TCs longitude - A low-level blocking ridge is north / northeast
of the TC
51Future Work
- Expand PRE database to include the western U.S.
(Pacific Basin TC) - Add composites / conceptual models for AT and ROT
PRE, and possibly other TC tracks (i.e. CG) - Develop a technique to identify / quantify PRE
rainfall in TC precipitation analyses - Perform modeling studies to interrogate the role
that TC have in modulating the strength of
poleward jets
52References
- Atallah, E. H., and L. F. Bosart, 2003 The
extratropical transition and precipitation
distribution of Hurricane Floyd (1999). Mon. Wea.
Rev., 131, 10631081. - Atallah, E., L. F. Bosart, and A. R. Aiyyer,
2007 Precipitation distribution associated with
landfalling tropical cyclones over the eastern
United States. Mon. Wea. Rev., 135, 21852206. - Bosart and F. H. Carr, 1978 A case study of
excessive rainfall centered around Wellsville,
New York, 20-21 June 1972. Mon. Wea. Rev., 106,
348362. - Bosart and D. B. Dean, 1991 The Agnes rainstorm
of June 1972 Surface feature evolution
culminating in inland storm redevelopment. Wea.
and Forecasting, 6, 515537. - Brooks, H. E., and D. J. Stensrud, 2000
Climatology of heavy rain events in the United
States from hourly precipitation observations.
Mon. Wea. Rev., 128, 11941201. - DeLuca, D. P., 2004 The distribution of
precipitation over the Northeast accompanying
landfalling and transitioning tropical cyclones.
M.S. thesis, Department of Earth and Atmospheric
Sciences, University at Albany, State University
of New York, 177 pp. - DiMego, G. J., and L. F. Bosart, 1982a The
transformation of tropical storm Agnes into an
extratropical cyclone. Part I The observed
fields and vertical motion computations. Mon.
Wea. Rev., 110, 385411. - LaPenta, K. D., and Coauthors, 1995 The
challenge of forecasting heavy rain and flooding
throughout the eastern region of the National
Weather Service. Part I Characteristics and
events. Wea. Forecasting, 10, 7890. - Schumacher, R. S., and R. H. Johnson, 2005
Organization and environmental properties of
extreme-rain-producing mesoscale convective
systems. Mon. Wea. Rev., 133, 961976. - Uccellini, L. W., and D. R. Johnson, 1979 The
coupling of upper and lower tropospheric jet
streaks and implications for the development of
severe convective storms. Mon. Wea. Rev., 107,
682703. - Ulbrich, C. W., and L. G. Lee, 2002 Rainfall
characteristics associated with the remnants of
tropical storm Helene in upstate South Carolina.
Wea. Forecasting, 17, 12571267.
53Any Questions ??
54WFO BGM Usage of HPC Products
- Days 4-7 Gridded Output (Medium Range)
- Common starting point
- HPC has access to more model data / better
ensembling capabilities (Master Blender) - Preferable to always populating with one model
(GMOS grids) - Lets us focus on short-term issues
55Usage of HPC Stuff (Shorter Range)
- Model diagnostics
- Will view discussions / graphics in more
complicated scenarios - Especially when theres significant model
discrepancies - QPF / Excessive Rainfall
- Will often use HPC QPF, or a blend of HPC and
other model QPFs in the first 24 48 hours - Depending on timing, may use data from a previous
model cycle - Will utilize Excessive Rainfall discussions /
graphics as guidance in heavy precipitation
situations - Winter Weather Desk
- Will typically view WWD graphics as a reality
check against our thinking - Particularly with mixed phase events / model
disagreements