[Tropical] Tropical Cyclone Discussion

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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



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