[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 292054
TCDAT3
TROPICAL STORM HANNA DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
500 PM EDT FRI AUG 29 2008

THE CENTER OF HANNA REMAINS NEAR THE WESTERN EDGE OF THE RATHER
SHAPELESS AREA OF DEEP CONVECTION SEEN IN SATELLITE IMAGERY.  A
1412 UTC ASCAT PASS FOUND WINDS OF 40 KT OVER THE NORTHEASTERN
SEMICIRCLE.  GIVEN THE LOW BIAS TYPICAL OF ASCAT WINDS IN THIS
RANGE...IT SUPPORTS MAINTAINING THE INITIAL INTENSITY AT 45 KT.
THIS INTENSITY IS ALSO SUPPORTED BY SATELLITE ESTIMATES FROM
TAFB AND SAB WHICH REMAIN T3.0 OR 45 KT.

WATER VAPOR IMAGERY SHOWS THAT THE UPPER-LEVEL LOW LOCATED A
COUPLE HUNDRED MILES WEST-NORTHWEST OF HANNA HAS NOT BUDGED
TODAY AND IT CONTINUES TO IMPART SOUTHWESTERLY SHEAR ON THE
TROPICAL CYCLONE.  THE DYNAMICAL MODELS REMAIN EMPHATIC
SUGGESTING THAT THE UPPER-LOW WILL MOVE WEST OR WEST-
SOUTHWESTWARD AND WEAKEN...ALLOWING HANNA TO GRADUALLY
STRENGTHEN.  THE NEW NHC INTENSITY FORECAST CONTINUES TO ALLOW FOR
SOME STRENGTHENING DURING THE NEXT COUPLE DAYS BUT SHOWS A LOWER
PEAK INTENSITY THAN WAS FORECAST IN THE PREVIOUS ADVISORY.  IN
ABOUT 3 DAYS...THE MODELS CONTINUE TO FORECAST STRONG NORTHWEST TO
NORTH UPPER-LEVEL WINDS OVER THE WESTERN ATLANTIC.  THESE WINDS ARE
PARTIALLY THE RESULT OF OUTFLOW FROM GUSTAV.  DESPITE THE HOSTILE
UPPER-LEVEL WIND FORECAST...THE INTENSITY GUIDANCE DOES NOT PREDICT
WEAKENING.  OUR INTENSITY FORECAST REMAINS ON THE LOW SIDE OF THE
GUIDANCE AND STILL ASSUMES THAT THE NORTHERLY SHEAR WILL HAVE A
NEGATIVE IMPACT ON HANNA'S INTENSITY.

HANNA CONTINUES MOVING WEST-NORTHWESTWARD OR 295/9.  IN
GENERAL...THE FORECAST GUIDANCE HAS COME INTO A LITTLE BETTER
AGREEMENT ON THE FUTURE TRACK OF HANNA.  THE TROPICAL STORM IS
FORECAST TO CONTINUE WEST-NORTHWESTWARD DURING THE NEXT 2
DAYS...FOLLOWED BY A TURN TOWARD THE WEST-SOUTHWEST.  THE HWRF
CONTINUES TO BE AN OUTLIER SHOWING A CYCLONIC LOOP NORTH OF THE
SOUTHEASTERN BAHAMAS.  THE NEW TRACK FORECAST IS VERY SIMILAR TO
THE PREVIOUS FORECAST THROUGH 48 HOURS...BUT IS A LITTLE FASTER
AND FARTHER WEST THEREAFTER.

FORECAST POSITIONS AND MAX WINDS

INITIAL      29/2100Z 21.8N  63.8W    45 KT
 12HR VT     30/0600Z 22.8N  65.4W    50 KT
 24HR VT     30/1800Z 24.0N  67.7W    55 KT
 36HR VT     31/0600Z 24.8N  69.8W    60 KT
 48HR VT     31/1800Z 25.0N  71.1W    65 KT
 72HR VT     01/1800Z 24.5N  72.5W    65 KT
 96HR VT     02/1800Z 23.7N  73.7W    60 KT
120HR VT     03/1800Z 23.0N  75.0W    60 KT

$$
FORECASTER BROWN



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