[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 291453
TCDAT3
TROPICAL STORM HANNA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
1100 AM EDT FRI AUG 29 2008

A 1031 UTC QUIKSCAT OVERPASS WAS VERY HELPFUL IN LOCATING THE CENTER
OF HANNA EARLY THIS MORNING.  VISIBLE IMAGERY SHOWED THAT THE CENTER
BRIEFLY BECAME EXPOSED...HOWEVER...NEW CONVECTION FORMED SINCE THAT
TIME AND THE CENTER IS POSITIONED JUST BENEATH THE COLDER CLOUD
TOPS.  DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB CONTINUE TO
SUPPORT 45 KT...SO THE INITIAL INTENSITY REMAINS UNCHANGED.  IN THE
NEAR TERM...THE DYNAMICAL MODELS SUGGEST THAT THE UPPER-LOW TO THE
WEST-NORTHWEST OF HANNA WILL MOVE WESTWARD AND WEAKEN...WHICH
SHOULD RELAX THE SOUTHWESTERLY SHEAR THAT IS CURRENTLY IMPINGING
UPON THE CYCLONE.  THE INTENSITY FORECAST FOLLOWS THIS SOLUTION
AND CALLS FOR GRADUAL STRENGTHENING DURING THE NEXT 2 DAYS...
BRINING HANNA TO HURRICANE STATUS.  THEREAFTER THERE IS A LARGE
AMOUNT OF UNCERTAINTY IN THE INTENSITY FORECAST. THE GLOBAL MODELS
PREDICT STRONG NORTHWEST TO NORTH UPPER-LEVEL WINDS OVER
HANNA...WHICH ONE WOULD THINK SHOULD HALT ADDITIONAL STRENGTHENING
OR EVEN WEAKEN THE STORM.  HOWEVER...NEARLY ALL OF THE INTENSITY
GUIDANCE SHOW STRENGTHENING OR LITTLE INTENSITY CHANGE DURING THAT
TIME.  ASSUMING THAT THE SHEAR WILL PRODUCE A NEGATIVE AFFECT ON
HANNA...THE NEW INTENSITY FORECAST FOLLOWS PERSISTENCE OF PREVIOUS
ADVISORY AND IS A LITTLE BELOW MOST OF THE GUIDANCE.

HANNA MOVED WEST-NORTHWESTWARD DURING THE PAST 12 HOURS AND THE
INITIAL MOTION ESTIMATE IS 285/10.  THE TRACK GUIDANCE IS
IN GOOD AGREEMENT THROUGH 48 HOURS ON A WEST-NORTHWEST TO NORTHWEST
MOTION.  THEREAFTER...THE MODELS GENERALLY SHOW A WEST-
SOUTHWESTWARD OR SOUTHWARD TURN..SOUTH OF A BUILDING RIDGE OVER
THE EASTERN UNITED STATES.  HOWEVER...THE SHARPNESS OF THE TURN
AND SPEED OF MOTION VARIES GREATLY.  THE NEW NHC TRACK HAS BEEN
ADJUSTED SOUTHWARD DURING THE FIRST COUPLE OF DAYS...MAINLY DUE TO
THE MORE WESTWARD INITIAL MOTION.  THIS IS IN CLOSE AGREEMENT WITH
THE MODEL CONSENSUS.  AFTER 72 HOURS...THE NEW TRACK IS A LITTLE
FASTER THAN THE PREVIOUS ADVISORY...BUT IS NOTICEABLY SLOWER THAN
THE UKMET AND GFDL MODELS.  THE HWRF...WHICH SHOWS A CYCLONIC LOOP
NORTH OF THE BAHAMAS AND A NORTHEASTWARD MOTION AT DAY 5...IS
CONSIDER AN OUTLIER AT THIS TIME.

INTERESTS IN THE SOUTHWESTERN BAHAMAS AND TURKS AND CAICOS SHOULD
MONITOR THE PROGRESS OF HANNA.  IMPACTS IN THESE AREAS COULD OCCUR
MUCH SOONER THAN INDICATED BY THE EXACT TRACK...ESPECIALLY IF THE
MORE NORTHWESTWARD MOTION DOES NOT MATERIALIZED LATER TODAY OR ON
SATURDAY.


FORECAST POSITIONS AND MAX WINDS

INITIAL      29/1500Z 21.3N  62.7W    45 KT
 12HR VT     30/0000Z 22.2N  64.5W    50 KT
 24HR VT     30/1200Z 23.6N  66.7W    55 KT
 36HR VT     31/0000Z 24.6N  68.6W    60 KT
 48HR VT     31/1200Z 25.1N  70.1W    70 KT
 72HR VT     01/1200Z 24.7N  71.6W    65 KT
 96HR VT     02/1200Z 24.0N  72.5W    65 KT
120HR VT     03/1200Z 23.0N  73.5W    60 KT

$$
FORECASTER BROWN

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