[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 300259
TCDAT3
TROPICAL STORM HANNA DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
1100 PM EDT FRI AUG 29 2008

CONVENTIONAL SATELLITE IMAGERY SUGGESTS THAT HANNA REMAINS WITHIN A
VERY HARSH VERTICAL WIND SHEAR ENVIRONMENT.  THE SURFACE
CIRCULATION...EXPOSED WELL WEST OF THE REMAINING CONVECTIVE
BAND...PASSED ABOUT 60 MILES NORTH OF BUOY 41043 WHICH RECORDED A
SEA LEVEL PRESSURE OF 1004 MB.  CONSEQUENTLY...HANNA'S CENTRAL
PRESSURE IS INCREASED SLIGHTLY TO 1002 MB BASED ON THIS DATA.  A
QUIKSCAT OVERPASS JUST CAME IN A FEW MINUTES AGO AND INDICATED THAT
THE CIRCULATION MAY BE JUST A BIT SOUTH OF THE ADVISORY POSITION AS
WELL AS ALSO REVEALING A FEW BELIEVABLE 40-45 KT WINDS OVER THE
NORTHEAST QUADRANT.  THEREFORE...THE INITIAL INTENSITY IS HELD AT
45 KT.  THE GLOBAL MODELS CONTINUE TO INDICATE THAT THE UPPER-LEVEL
LOW LOCATED A FEW HUNDRED MILES WEST-NORTHWEST OF CYCLONE WILL
EITHER INCREASE IN DISTANCE BETWEEN THE TWO FEATURES WITH TIME OR
WEAKEN AND OPEN UP INTO A TROUGH.  THE SHIPS MODEL FOLLOWS SUIT BY
SUGGESTING THAT THE SHEAR WILL DECREASE IN 12 TO 24 HOURS...WHICH
IS REFLECTED IN THE INTENSITY FORECAST WITH GRADUAL STRENGTHENING
THROUGH THE 72 HOUR PERIOD.  THROUGH THE REMAINING PORTION OF THE
FORECAST...THE LARGE-SCALE MODELS SHOW STRONG NORTH TO
NORTHWESTERLY UPPER-LEVEL WINDS SETTING UP OVER THE WESTERN
ATLANTIC...WHICH COULD ALSO BE INFLUENCED BY HURRICANE GUSTAV'S
OUTFLOW PATTERN.  SINCE THERE IS A CONSENSUS IN THE DEVELOPMENT OF
AN INHIBITING SYNOPTIC UPPER-LEVEL PATTERN...A WEAKENING IS
INDICATED THROUGH DAY 5.

INITIAL MOTION IS ESTIMATED AT 295/12...WITHIN THE DEEP LAYER
EAST-SOUTHEASTERLY FLOW OF THE SUBTROPICAL RIDGE TO THE NORTH OF
THE CYCLONE.  THE FORECAST PHILOSOPHY REMAINS INTACT FROM THE
PREVIOUS ADVISORY...WHICH FOLLOWS CLOSELY TO THE DYNAMICAL MODEL
BLEND THROUGH 72 HOURS.  BEYOND THE DAY 3 PERIOD...THE OFFICIAL
FORECAST IS NUDGED TOWARD THE PREVIOUS TRACK AND A BLEND OF THE GFS
AND UKMET MODELS WHICH APPEAR TO BE DEPICTING THE SHEARED VERTICAL
STRUCTURE OF THE SYSTEM MORE ACCURATELY.

FORECAST POSITIONS AND MAX WINDS

INITIAL      30/0300Z 22.1N  65.3W    45 KT
 12HR VT     30/1200Z 22.9N  67.0W    50 KT
 24HR VT     31/0000Z 23.9N  69.2W    55 KT
 36HR VT     31/1200Z 24.5N  70.8W    60 KT
 48HR VT     01/0000Z 24.6N  72.1W    65 KT
 72HR VT     02/0000Z 24.4N  73.4W    65 KT
 96HR VT     03/0000Z 23.6N  75.0W    60 KT
120HR VT     04/0000Z 23.0N  76.3W    55 KT

$$
FORECASTER ROBERTS



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