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Tropical Depression SIX (Text)

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TROPICAL DEPRESSION SIX DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062006
1100 PM EDT MON SEP 04 2006
 
THERE WAS CONSIDERABLE DIFFICULTY IN TRYING TO DETERMINE A CENTER
POSITION THIS EVENING. BUOY 41041 LOCATED IN THE SOUTHERN PORTION
OF THE ELONGATED CYCLONIC CIRCULATION INDICATED A WEAK CIRCULATION
HAD PASSED OVER OR NEAR THAT BUOY AROUND 00Z. THE LOW-LEVEL
CIRCULATION CENTER THAT WE HAVE BEEN TRACKING THE PAST DAY OR SO
HAS BECOME LESS OBVIOUS IN QUIKSCAT AND CONVENTIONAL SATELLITE
IMAGERY. THEREFORE...THE ADVISORY POSITION IS A BLEND OF
CONVENTIONAL FIX POSITIONS AND A 04/2130Z QUIKSCAT OVERPASS. THIS
POSITION IS NORTH OF THE CENTER OF THE CYCLONIC ENVELOPE NOTED IN
NIGHTTIME VISIBLE IMAGERY AND QUIKSCAT DATA...AND LEANS CLOSER TO
THE DEEP CONVECTIVE BURST THAT HAS DEVELOPED TO THE NORTH.
 
THE INITIAL MOTION ESTIMATE IS 300/11. UNTIL THE CENTER CONSOLIDATES
AND BECOMES BETTER DEFINED WITHIN THE CONVECTIVE PATTERN...THERE
MAY BE SOME REFORMATION OF THE CIRCULATION CENTER AS IT MIGRATES
TOWARD ANY CONVECTIVE BURSTS. HOWEVER...THE OVERALL MOTION OF THE
LARGER CYCLONIC ENVELOPE SHOULD BE WEST-NORTHWESTWARD THROUGHOUT
THE FORECAST PERIOD AS THE SYSTEM MOVES ALONG THE SOUTHERN
PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE LOCATED TO THE NORTH.
BY DAY 5...THE CYCLONE IS EXPECTED TO TURN A LITTLE MORE
NORTHWESTWARD TOWARD A WEAKNESS IN THE RIDGE THAT IS FORECAST TO
DEVELOP BETWEEN 65W-75W LONGITUDE. HOWEVER...THE WEAK LOW-LATITUDE
SHORTWAVE TROUGH THAT IS EXPECTED TO CREATE THE BREAK IN THE RIDGE
EAST OF FLORIDA IS FORECAST BY THE GLOBAL MODELS TO PHASE UP WITH A
MUCH STRONGER MID-LATITUDE TROUGH THAT IS EXPECTED TO SWING RAPIDLY
EASTWARD TOWARD THE U.S. EAST COAST. IT SHOULD BE POINTED OUT THAT
OFTENTIMES STRONGER MID-LATITUDE SHORTWAVES WILL BYPASS AND NOT
LINK UP WITH WEAKER TROUGHS SITUATED OVER LOWER LATITUDES. AS A
RESULT...THE OFFICIAL FORECAST TRACK INDICATES ONLY A SLIGHT
POLEWARD BEND BY DAY 5...WHICH IS SIMILAR TO THE MODEL CONSENSUS.

WATER VAPOR IMAGERY INDICATES THE DEPRESSION HAS BEEN FIGHTING OFF
SOME DRY AIR THAT HAS BEEN PUNCHING INTO THE CENTER OF THE
CIRCULATION THE PAST 12 HOURS OR SO...ALONG WITH SOME LIGHT TO
MODERATE SOUTHWESTERLY VERTICAL SHEAR. THESE CONDITIONS ARE
EXPECTED TO PERSIST FOR THE NEXT 72 HOURS...SO ONLY GRADUAL
STRENGTHENING IS FORECAST. HOWEVER...AFTER 72HOURS...THE SHIPS
MODEL IS FORECASTING THE SHEAR TO DECREASE TO LESS THAN 10 KT...
AND BY 96-120 HOURS BE NEAR ZERO. THAT IS WHEN MORE SIGNIFICANT
INTENSIFICATION COULD OCCUR AND THIS IS REFLECTED IN THE OFFICIAL
FORECAST. THE SHIPS MODEL BRINGS THE CYCLONE TO 87 KT BY 120 HOURS
...WHEREAS THE GFDL STILL MAKES THE SYSTEM A MAJOR HURRICANE AT THAT
TIME. DUE TO THE UNCERTAINTY IS THE EXACT EVOLUTION OF THE
UPPER-LEVEL FLOW PATTERN AS INDICATED BY THE DIFFERENT SOLUTIONS IN
THE VARIOUS GLOBAL MODELS...THE OFFICIAL INTENSITY FORECAST WILL
REMAIN ON THE CONSERVATIVE SIDE AND BELOW THE AVAILABLE GUIDANCE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      05/0300Z 17.3N  44.8W    30 KT
 12HR VT     05/1200Z 17.9N  45.9W    35 KT
 24HR VT     06/0000Z 18.6N  47.7W    40 KT
 36HR VT     06/1200Z 19.2N  49.5W    45 KT
 48HR VT     07/0000Z 19.8N  51.5W    50 KT
 72HR VT     08/0000Z 21.0N  56.0W    60 KT
 96HR VT     09/0000Z 22.0N  60.5W    70 KT
120HR VT     10/0000Z 24.0N  65.0W    80 KT
 
$$
FORECASTER STEWART
 
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