Special Weather Briefing Isaac 530 PM - 08/29/ Keith Stellman Meteorologist National Weather Service Shreveport, Louisiana

Isaac Summary A little better agreement this afternoon A little better agreement this afternoon Official Isaac Forecast Official Isaac Forecast Winnfield -> Ruston -> Prescott, AR Winnfield -> Ruston -> Prescott, AR A little Faster in moving out A little Faster in moving out Rainfall threat highest Rainfall threat highest Jena->Monroe->El Dorado->Hope/Nashville Jena->Monroe->El Dorado->Hope/Nashville Model Data Model Data A couple models still on a more westward track A couple models still on a more westward track Largest impacts over N LA/S AR, but some wind impacts into E TX/SE OK possible Largest impacts over N LA/S AR, but some wind impacts into E TX/SE OK possible National Weather Service Shreveport, Louisiana

Radar Imagery

Current Position H Ridge to the northwest…causing slower motion. It is forecast to shift east and allow Isaac to sling northward

Model Forecast of Upper Ridge H Ridge begins bridging east north of Isaac GFS Thu AM GFS Thu PM H Ridge gets East of Isaac and begins to sling it north

Timing + Precip (Thu -> 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

Official Rainfall Forecast Locally higher totals may be possible

Official Forecast Impacts: Flooding N LA N LA Greatest risk for flooding Greatest risk for flooding Overnight Wed -Fri AM Overnight Wed -Fri AM S AR S AR 2 nd greatest risk area 2 nd greatest risk area Early Thu AM-Fri PM Early Thu AM-Fri PM Extreme E TX Extreme E TX..Only in a western track scenario..Only in a western track scenario Flash Flooding Possible

Official Forecast Impacts: Winds 8 PM Wed Tropical Storm force winds N Central LA N Central LA ~40-45 mph ~40-45 mph Wed night-most of Thu Wed night-most of Thu SW AR/SE OK SW AR/SE OK mph mph Peak in 30s on Thu Peak in 30s on Thu Deep E TX Deep E TX mph mph Late Wed PM – most of Thu Late Wed PM – most of Thu E TX E TX mph mph Thu Thu 5 AM Thu

Official Forecast Impacts: Winds 3 PM Thu Tropical Storm force winds Timing of TS winds Timing of TS winds Primarily in gusts Primarily in gusts Central LA Central LA After 12 AM -> 5 PM After 12 AM -> 5 PM North West LA North West LA 1 PM - > 8 PM 1 PM - > 8 PM North Central/North East LA North Central/North East LA 5 AM -> 9 PM 5 AM -> 9 PM 7 PM Thu

Official NHC Track Forecast 1 AM Friday Latest track forecast 1 PM Thu 1 AM Thu Potential Tropical Storm force winds area

Official Forecast Impacts: Tornadoes Thu AM – Fri AM US 165 Corridor-> eastward US 165 Corridor-> eastward Most at risk Most at risk Quick spin-ups Quick spin-ups Not much lead time Not much lead time Elsewhere Elsewhere Can’t rule it out, but very low risk Can’t rule it out, but very low risk

Watches/Warnings/Advisories Flash Flood Watch 7 AM Thu - 7 PM Thu Topical Storm Warning Flash Flood Watch 7 PM Wed - 1 PM Thu

Track Model Spread Key is in first 24 hour spread

“What if” Isaac is a little West Officialtrack “What if” track

Potential Impacts On forecast Track On 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 PM Greatest impact timeframe: Thu/Thu PM Winds mph with higher gusts Late Wed PM-Thu PM for N/LA; ~25 mph with higher gusts for S AR Winds mph with higher gusts Late Wed PM-Thu PM for N/LA; ~25 mph with higher gusts for S AR Prime tornado threat area east of US 165 Prime tornado threat area east of US 165 Power outages possible primarily in LA east of I-49 corridor Power outages possible primarily in LA east of I-49 corridor E TX/SE OK E TX/SE OK Rainfall: 1-2” isolated 3” Rainfall: 1-2” isolated 3” Winds mph with higher gusts Thu AM-Thu PM Winds mph with higher gusts Thu AM-Thu PM

NEXT CONFERENCE CALL: August 30, 10:00 AM National Weather Service Shreveport, Louisiana