SEVERE WEATHER WARNINGS

ATTENTION COASTAL STATES BORDERING THE GULF OF MEXICO

000
WTNT42 KNHC 280904
TCDAT2
TROPICAL STORM GUSTAV DISCUSSION NUMBER 13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072008
500 AM EDT THU AUG 28 2008

AN AIR FORCE RECONNAISSANCE PLANE HAS FOUND A SURPRISE THIS MORNING. GUSTAV HAS EITHER REFORMED TO THE SOUTH OR BEEN MOVING MORE TO THE SOUTH-SOUTHWEST OVERNIGHT. IN ADDITION ... THE PRESSURE IS DOWN 10 MB DURING THE LAST SIX HOURS. THE PLANE HAS NOT YET SAMPLED THE ENTIRE STORM...BUT IT IS ASSUMED THE WINDS HAVE COME UP SLIGHTLY WITH THE SIGNIFICANT PRESSURE FALL AND THE INITIAL INTENSITY IS INCREASED TO 45 KT. MID-LEVEL DRY AIR...SOME NORTHEASTERLY SHEAR...AND INTERACTION WITH JAMAICA MAY LIMIT THE INTENSIFICATION OF THIS SYSTEM DURING THE NEXT DAY OR SO. THUS THE OFFICIAL INTENSITY FORECAST IS ONLY SLIGHTLY RAISED FROM EARLIER. THEREAFTER...THE GLOBAL MODELS ARE FORECASTING AN UPPER ANTICYCLONE TO BE NEAR THE CENTER OF GUSTAV...WHICH WOULD BE QUITE FAVORABLE FOR STRENGTHENING. IT IS EXPECTED THAT GUSTAV WILL BE A POWERFUL HURRICANE AS IT MOVES INTO THE SOUTHERN GULF OF MEXICO ON SUNDAY. SOUTHWESTERLY VERTICAL WIND SHEAR COULD INCREASE LATE IN THE PERIOD WHEN THE SYSTEM IS FORECAST TO BE IN THE NORTHERN GULF BUT THERE IS CONSIDERABLY UNCERTAINTY AT THAT TIME.

THE BEST ESTIMATE OF INITIAL MOTION IS 215/7. THE REFORMATION OF THE CENTER HAS CAUSED A BIG SOUTHWARD CHANGE IN THE EARLY PART OF THE FORECAST...AND GUSTAV IS NOW FORECAST TO PASS NEAR THE SOUTH COAST OF JAMAICA. THE NORTHEAST-SOUTHWEST ORIENTED RIDGE CENTERED OVER THE FLORIDA PENINSULA THAT HAS BEEN CAUSING THIS SOUTHWESTWARD MOTION IS EXPECTED TO WEAKEN OVER THE NEXT FEW DAYS. THIS SHOULD ALLOW GUSTAV TO TURN MORE TO THE WEST AND THEN NORTHWEST AROUND THE TIME IT ENTERS THE GULF OF MEXICO. A MID-LATITUDE HIGH IS FORECAST
TO BE IN THE OHIO VALLEY IN ABOUT 5 DAYS...WHICH MAY CONTINUE STEERING THE STORM IN A NORTHWESTWARD FASHION RATHER THAN ALLOW A MORE NORTHWARD MOTION LIKE THE GFDL SUGGESTS. THE OFFICIAL FORECAST IS SHIFTED WESTWARD IN THE LONGER-TERM...ON THE EASTERN SIDE OF THE MODEL GUIDANCE ENVELOPE...BUT THE ECMWF AND GFDL ARE TO THE RIGHT OF THE NHC FORECAST.

FORECAST POSITIONS AND MAX WINDS

INITIAL      28/0900Z 17.8N 75.6W    45 KT
12HR VT     28/1800Z 17.5N 77.0W    55 KT
24HR VT     29/0600Z 17.8N 78.5W    60 KT
36HR VT     29/1800Z 18.5N 80.3W    65 KT
48HR VT     30/0600Z 19.5N 82.0W    75 KT
72HR VT     31/0600Z 22.0N 85.5W    95 KT
96HR VT     01/0600Z 26.0N 89.0W   100 KT
120HR VT     02/0600Z 28.5N 91.0W   100 KT

$$
FORECASTER BLAKE/AVILA