[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 301447
TCDAT3
TROPICAL STORM HANNA DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
1100 AM EDT SAT AUG 30 2008

HANNA CONTINUES TO PRODUCE A LARGE AREA OF DEEP CONVECTION WITH
CLOUD TOP TEMPERATURES BELOW -80 DEGREES C. HOWEVER...THE CENTER OF
THE TROPICAL CYCLONE IS LOCATED NEAR THE SOUTHWESTERN EDGE OF THIS
CONVECTION.  THE EXACT CENTER HAS BEEN DIFFICULT TO LOCATE AS A
COUPLE OF SMALL VORTICES HAVE BEEN SEEN ROTATING AROUND THE LARGER
CIRCULATION THIS MORNING.  SATELLITE INTENSITY ESTIMATES REMAIN
T3.0 OR 45 KT AND AN EARLIER QUIKSCAT PASS SUGGEST MAXIMUM WINDS
WERE NEAR THAT VALUE.  THERE WERE SOME STRONGER WINDS SEEN IN THE
QUIKSCAT DATA...BUT THESE WINDS WERE WELL REMOVED FROM THE CENTER
AND APPEAR TO HAVE BEEN RAIN-INFLATED.

THE SOMEWHAT UNCERTAIN INITIAL MOTION ESTIMATE IS 275/7.  HANNA HAS
CONTINUED TO MOVE MORE WESTWARD DURING THE PAST 12-24 HOURS...WHICH
HAS REQUIRED A LITTLE SOUTHWARD ADJUSTMENT TO THE TRACK FORECAST IN
THE SHORT-TERM.  THE TRACK GUIDANCE PREDICTS A GENERAL WEST TO
WEST-NORTHWEST MOTION DURING THE NEXT 24-36 HOURS.  THEREAFTER...
THERE IS A GREAT DEAL OF SPREAD AMONG THE MODELS...AS A STRONG HIGH
PRESSURE RIDGE BUILDS OVER THE EASTERN UNITED STATES.  THE GFDL AND
HWRF RESPOND BY SHOWING A VERY SLOW AND ERRATIC MOTION IN ABOUT 3
DAYS...WHILE THE UKMET TURNS HANNA SOUTHWESTWARD TOWARDS EASTERN
CUBA.  VERY LATE IN THE PERIOD...THE HIGH OVER THE EASTERN U.S. IS
FORECAST TO MOVE OFF THE EAST COAST INTO THE WESTERN ATLANTIC AND
SEVERAL OF THE FORECAST MODELS NOW INDICATE A WEST-NORTHWESTWARD
AROUND DAY 5.  THE NEW FORECAST WHICH IS VERY SIMILAR TO THE
PREVIOUS ADVISORY...BUT SMOOTHS THROUGH THESE POSSIBLE UNDULATIONS
AND SHOWS A SLOW WESTWARD MOTION BETWEEN 72-120 HOURS. THE NEW
TRACK IS GENERALLY ALONG OR JUST SOUTH OF THE MODEL CONSENSUS.

THE MUCH DISCUSSED UPPER-LOW JUST WEST OF THE STORM APPEARS TO HAVE
WEAKENED A LITTLE THIS MORNING.  THE SHIPS GUIDANCE SUGGESTS THE
WESTERLY SHEAR MAY RELAX JUST A LITTLE OVER THE NEXT 24 HOURS.
GIVEN THE RESILIENCE OF HANNA...THE OFFICIAL FORECAST SHOWS A
LITTLE STRENGTHENING DURING THE NEXT DAY OR SO.
THEREAFTER...STRONG NORTHWEST TO NORTH UPPER-LEVEL WINDS ARE
FORECAST...SO THE OFFICIAL INTENSITY FORECAST NOW KEEPS HANNA JUST
BELOW HURRICANE STRENGTH.  IT SHOULD BE NOTED ONCE AGAIN...THAT THE
NHC INTENSITY FORECAST REMAINS BELOW ALL OF THE RELIABLE GUIDANCE.

BASED ON THE NEW FORECAST TRACK...THE GOVERNMENT OF THE BAHAMAS HAS
ISSUED A TROPICAL STORM WATCH FOR THE SOUTHEASTERN BAHAMAS AND
TURKS AND CAICOS ISLANDS.

FORECAST POSITIONS AND MAX WINDS

INITIAL      30/1500Z 21.9N  66.4W    45 KT
 12HR VT     31/0000Z 22.4N  67.9W    50 KT
 24HR VT     31/1200Z 22.9N  69.6W    55 KT
 36HR VT     01/0000Z 23.2N  71.0W    60 KT
 48HR VT     01/1200Z 23.2N  72.1W    60 KT
 72HR VT     02/1200Z 23.0N  73.5W    55 KT
 96HR VT     03/1200Z 23.0N  75.0W    55 KT
120HR VT     04/1200Z 23.0N  76.5W    55 KT

$$
FORECASTER BROWN

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