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Special Weather BriefingSpecial Weather BriefingIsaacIsaac
530 PM - 08/29/2012 530 PM - 08/29/2012
www.srh.noaa.gov/shv/briefingwww.srh.noaa.gov/shv/briefing
Keith StellmanKeith StellmanMeteorologistMeteorologist
National Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana
Isaac Summary A little better agreement this afternoon A little better agreement this afternoon Official Isaac ForecastOfficial Isaac Forecast
Winnfield -> Ruston -> Prescott, ARWinnfield -> Ruston -> Prescott, AR A little Faster in moving outA little Faster in moving out Rainfall threat highestRainfall threat highest
Jena->Monroe->El Dorado->Hope/NashvilleJena->Monroe->El Dorado->Hope/Nashville Model DataModel Data
A couple models still on a more westward trackA couple models still on a more westward track Largest impacts over N LA/S AR, but some wind Largest impacts over N LA/S AR, but some wind
impacts into E TX/SE OK possibleimpacts into E TX/SE OK possible
National Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana
Radar ImageryRadar Imagery
Current PositionCurrent Position
H
Ridge to the northwest…causing Ridge to the northwest…causing slower motion. slower motion.
It is forecast to shift east and allow It is forecast to shift east and allow Isaac to sling northwardIsaac to sling northward
Model Forecast of Upper Model Forecast of Upper RidgeRidge
H
Ridge begins bridging east Ridge begins bridging east north of Isaacnorth of Isaac
GFS forecast @ Thu AM GFS forecast @ Thu AM
GFS forecast @ Thu PM GFS forecast @ Thu PM
H
Ridge gets East of Isaac and Ridge gets East of Isaac and begins to sling it northbegins to sling it north
Timing + Precip (Thu -> Timing + Precip (Thu -> Fri)Fri)Midnight – 6 AM 6 AM - Noon
Noon – 6 PM 6 PM - Midnight Midnight – 6 AM
**based on GFS track which is
~30 miles west of official
OfficialOfficial Rainfall Forecast Rainfall Forecast
Locally higher totals may be possible
Official Forecast Official Forecast Impacts: Impacts: FloodingFlooding N LAN LA
Greatest risk for Greatest risk for floodingflooding
Overnight Wed -Fri Overnight Wed -Fri AMAM
S ARS AR 22ndnd greatest risk area greatest risk area Early Thu AM-Fri PMEarly Thu AM-Fri PM
Extreme E TXExtreme E TX ..Only in a western ..Only in a western
track scenariotrack scenario
Flash Flooding Flash Flooding PossiblePossible
Official Forecast Official Forecast Impacts: Impacts: WindsWinds
8 PM Wed8 PM WedTropical Tropical
Storm force Storm force windswinds
N Central LA N Central LA ~40-45 mph~40-45 mph Wed night-most of Wed night-most of
Thu Thu
SW AR/SE OK SW AR/SE OK 15-20 mph15-20 mph Peak in 30s on ThuPeak in 30s on Thu
Deep E TXDeep E TX 20-25 mph 20-25 mph Late Wed PM – Late Wed PM –
most of Thumost of Thu
E TX E TX 10-15 mph10-15 mph ThuThu
5 AM Thu5 AM Thu
Official Forecast Official Forecast Impacts: Impacts: WindsWinds
3 PM Thu3 PM ThuTropical Tropical
Storm force Storm force windswinds
Timing of TS Timing of TS windswinds Primarily in gustsPrimarily in gusts
Central LACentral LA After 12 AM -> 5 PMAfter 12 AM -> 5 PM
North West LANorth West LA 1 PM - > 8 PM1 PM - > 8 PM
North North Central/North Central/North East LAEast LA 5 AM -> 9 PM5 AM -> 9 PM
7 PM Thu7 PM Thu
Official NHC Track ForecastOfficial NHC Track Forecast
1 AM 1 AM FridayFriday
Latest trackforecast
1 PM 1 PM ThuThu
1 AM 1 AM ThuThu
Potential Potential Tropical Tropical
Storm force Storm force winds areawinds area
Official Forecast Official Forecast Impacts: Impacts: TornadoesTornadoes
Thu AM – Fri AM
US 165 US 165 Corridor-> Corridor-> eastwardeastward Most at riskMost at risk Quick spin-Quick spin-
upsups Not much Not much
lead timelead time
ElsewhereElsewhere Can’t rule it Can’t rule it
out, but very out, but very low risklow risk
Watches/Warnings/Watches/Warnings/AdvisoriesAdvisories
Flash Flood Watch
7 AM Thu - 7 PM Thu
Topical Storm
WarningFlash Flood
Watch7 PM Wed - 1 PM Thu
Track Model SpreadTrack Model Spread
Key is in first 24 hour
spread
““What if” Isaac is a little What if” Isaac is a little WestWest
Off
icial
Off
icial
track
track““What if”What if”
tracktrack
Potential ImpactsPotential Impacts On forecast TrackOn forecast Track
N LA/S AR N LA/S AR Heavy rainfall/flooding (5-10”) Heavy rainfall/flooding (5-10”) Greatest impact timeframe: Thu/Thu PMGreatest impact timeframe: Thu/Thu PM Winds 40-45 mph with higher gusts Late Wed PM-Thu Winds 40-45 mph with higher gusts Late Wed PM-Thu
PM for N/LA; ~25 mph with higher gusts for S ARPM for N/LA; ~25 mph with higher gusts for S AR Prime tornado threat area east of US 165Prime tornado threat area east of US 165 Power outages possible primarily in LA east of I-49 Power outages possible primarily in LA east of I-49
corridorcorridor E TX/SE OKE TX/SE OK
Rainfall: 1-2” isolated 3”Rainfall: 1-2” isolated 3” Winds 20-30 mph with higher gusts Thu AM-Thu PMWinds 20-30 mph with higher gusts Thu AM-Thu PM
NEXT CONFERENCE CALL:
August 30, 2012 @ 10:00 AMAugust 30, 2012 @ 10:00 AM
www.srh.noaa.gov/shv/briefing
National Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana