Tuesday, August 28, 2012

T.S. Isaac Discussion #27

000
WTNT44 KNHC 272058
TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL  AL092012
400 PM CDT MON AUG 27 2012

THE MUCH ANTICIPATED INTENSIFICATION 
PROCESS APPEARS TO HAVE FINALLY 
STARTED BASED ON REPORTS FROM AN AIR 
FORCE RESERVE RECONNAISSANCE 
AIRCRAFT AND FROM NEARBY NOAA BUOY 
42003. THE CENTRAL PRESSURE HAS 
DECREASED BY AT LEAST 7 MB SINCE THE 
PREVIOUS ADVISORY. THE HIGHEST FLIGHT-
LEVEL WINDS OBSERVED HAVE BEEN 74 KT 
IN THE SOUTHWEST QUADRANT AND THE 
HIGHEST BIAS-ADJUSTED SFMR WINDS ARE 
NEAR 58 KT. THESE DATA SUPPORT AN 
INTENSITY OF 60 KT.

ISAAC WOBBLED WESTWARD THIS 
AFTERNOON...BUT A REPRESENTATIVE 
INITIAL MOTION ESTIMATE IS 305/10. THE 
LATEST 12Z NHC MODEL GUIDANCE IS IN 
BETTER AGREEMENT ON A WEST-
NORTHWEST TO NORTHWEST MOTION 
TOWARD THE SOUTHEAST LOUISIANA AND 
MISSISSIPPI COASTAL AREAS OVER THE 
NEXT 36-48 HOURS. AFTER 48 
HOURS...HOWEVER...THE MODEL GUIDANCE 
REMAINS DIVERGENT ON THE HANDLING OF 
A SHORTWAVE TROUGH FORECAST TO DIG 
SOUTHEASTWARD FROM THE UPPER 
MIDWEST AND INTO THE MID-ATLANTIC 
REGION...FOLLOWED BY A RIDGE BUILDING 
IN BEHIND THE TROUGH. THE GFS AND 
ECMWF...OUR MOST RELIABLE MODELS... 
NOW HAVE VERY SIMILAR SOLUTIONS 
THROUGH DAY 5...AND THE OFFICIAL 
FORECAST TRACK IS BETWEEN THOSE TWO 
MODELS.

SATELLITE DATA INDICATE ISAAC HAS 
BECOME BETTER ORGANIZED OVER THE 
PAST 6 HOURS WITH THE DEVELOPMENT OF 
A CENTRAL DENSE OVERCAST CLOUD 
PATTERN OVER THE CENTER ALONG WITH A 
DEVELOPING EYE IN RECON DATA. 
SATELLITE DATA T-NUMBERS HAVE 
INCREASED TO T4.5/77 KT FROM TAFB AND 
SAB. RECON WIND DATA INDICATE THE 
RADIUS OF MAXIMUM WINDS HAS ALSO 
PULLED INWARD TO ABOUT 30 N MI. 
ALTHOUGH ADDITIONAL CONVECTION HAS 
BEEN DEVELOPING IN THE NORTHEASTERN 
QUADRANT...DRY MID-LEVEL AIR STILL 
LURKS JUST TO THE EAST AND SOUTHEAST 
OF THE CDO FEATURE... WHICH COULD BE 
ENTRAINED INTO THE INNER CORE AT ANY 
TIME AND DISRUPT THE DEVELOPMENT 
PROCESS. DUE TO THE PROXIMITY OF DRY 
AIR...THE INTENSITY FORECAST INDICATES 
ONLY MODEST DEVELOPMENT FOR THE 
NEXT 24 HOURS. 

HOWEVER...STRENGTHENING IS EXPECTED 
TO CONTINUE  RIGHT UP UNTIL LANDFALL 
OCCURS DUE TO THE VERY WARM WATERS 
THE CYCLONE WILL BE PASSING OVER AND 
THE VERY FAVORABLE UPPER-LEVEL 
OUTFLOW REGIME THAT ISAAC IS 
FORECAST TO DEVELOP BY 24 HOURS. THE 
INTENSITY FORECAST IS JUST SLIGHTLY 
HIGHER THAN THE MODEL GUIDANCE.

BECAUSE SIGNIFICANT HAZARDS EXTEND 
WELL AWAY FROM THE CENTER...IT IS 
IMPORTANT NOT TO FOCUS ON THE EXACT 
FORECAST TRACK. THE SLOW FORWARD 
SPED OF AROUND 5 KT AFTER LANDFALL 
WILL RESULT IN A HEAVY RAIN AND FLOOD 
SITUATION FOR PORTIONS OF THE CENTRAL 
GULF COAST AND LOWER MISSISSIPPI 
VALLEY REGIONS.

FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 26.4N  86.2W   60 KT  70 MPH
 12H  28/0600Z 27.4N  87.5W   70 KT  80 MPH
 24H  28/1800Z 28.6N  89.0W   80 KT  90 MPH
 36H  29/0600Z 29.5N  90.0W   85 KT 100 MPH...NEAR THE COAST
 48H  29/1800Z 30.3N  90.7W   75 KT  85 MPH...INLAND
 72H  30/1800Z 32.2N  91.8W   35 KT  40 MPH...INLAND
 96H  31/1800Z 35.9N  92.1W   25 KT  30 MPH...INLAND
120H  01/1800Z 38.7N  89.3W   20 KT  25 MPH...INLAND

$$
FORECASTER STEWART