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
