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