Tropical Storm DANNY

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TROPICAL STORM DANNY DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL052009
500 AM EDT THU AUG 27 2009
 
DATA FROM NOAA BUOY 41047 AND THE AIR FORCE RECONNAISSANCE AIRCRAFT
HAVE BEEN CRITICAL IN LOCATING THE BROAD AND ELONGATED CIRCULATION
OF DANNY THIS MORNING...WHICH APPEARS TO HAVE MADE ANOTHER
NORTHWARD REFORMATION. THE AIR FORCE PLANE FOUND 55 KT WINDS AT 850
MB AND DROPSONDE AND RELIABLE SFMR WINDS OF ABOUT 45 KT. AN EARLIER
NOAA HURRICANE HUNTER AIRCRAFT SHOWED 12000 FT WINDS OF 66 KT AND
RELIABLE SFMR VALUES OF 45-50 KT. THE NOAA SFMR DATA ALSO
REASONABLY FIT A 2254 UTC QUIKSCAT PASS WHICH HAD A FEW 50 KT WIND
BARBS. THEREFORE...THE ADVISORY INTENSITY IS SET TO 50 KT. IT
SHOULD BE NOTED THAT DANNY DOES NOT HAVE A TYPICAL TROPICAL CYCLONE
STRUCTURE AND HAS MOST OF THE STRONG WINDS LOCATED WELL NORTH AND
EAST OF THE CENTER.
 
WITH ALL THE CENTER REFORMATIONS...THE INITIAL MOTION IS JUST ABOUT
IMPOSSIBLE TO DETERMINE...BUT THE BEST ESTIMATE IS 315/9. DESPITE
THE INITIAL UNCERTAINTY...THE MODELS ARE IN EXCELLENT AGREEMENT ON
A TURN TOWARD THE NORTH ON FRIDAY AS DANNY MOVES BETWEEN A RIDGE
OVER THE WESTERN ATLANTIC OCEAN AND A SHORTWAVE TROUGH OVER THE
SOUTHEASTERN UNITED STATES. THE STORM SHOULD THEN ACCELERATE
NORTHEASTWARD DUE TO INCREASING FLOW AHEAD OF A LARGER TROUGH OVER
THE GREAT LAKES. THE OFFICIAL FORECAST IS SHIFTED EASTWARD BECAUSE
OF THE CENTER REFORMATION AND THE GOOD TRACK MODEL AGREEMENT.
HOWEVER...ANY SIGNIFICANT DEVIATION TO THE WEST OF THE FORECAST
TRACK WOULD BRING DANNY CLOSER TO THE U.S. EAST COAST.  
 
WHILE SHEAR IS RELATIVELY LIGHT NEAR DANNY FOR THE TIME BEING...
GLOBAL MODELS INCREASE THE SHEAR WITHIN A DAY OR SO. DESPITE THIS
PATTERN CHANGE...ALL OF THE RELIABLE INTENSITY MODELS MAKE DANNY A
HURRICANE IN A COUPLE OF DAYS...AND MOST OF THE GLOBAL MODELS SHOW
THE SYSTEM INTENSIFYING DESPITE THE SHEAR. SOME OF THIS INCREASE IN
STRENGTH COULD BE DUE TO BAROCLINIC INFLUENCES AS THE GLOBAL MODELS
ARE SHOWING A RATHER DIFFLUENT PATTERN NEAR THE TROPICAL CYCLONE
WITH STRONG JET DYNAMICS. HOWEVER...THIS WOULD ARGUE MORE FOR A
STRONG EXTRATROPICAL CYCLONE RATHER THAN A TROPICAL CYCLONE. THE
OFFICIAL FORECAST STILL SHOWS THIS SYSTEM TO BE A HURRICANE IN A
COUPLE OF DAYS BUT GIVEN THE SEEMINGLY UNFAVORABLE ENVIRONMENT...
THE NHC FORECAST IS LOWER THAN MOST OF THE GUIDANCE AND MAKES DANNY
EXTRATROPICAL BY 72 HOURS.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/0900Z 27.4N  72.1W    50 KT
 12HR VT     27/1800Z 28.4N  73.1W    50 KT
 24HR VT     28/0600Z 30.0N  74.0W    55 KT
 36HR VT     28/1800Z 32.3N  74.0W    60 KT
 48HR VT     29/0600Z 35.7N  72.9W    65 KT
 72HR VT     30/0600Z 44.0N  66.5W    65 KT...EXTRATROPICAL
 96HR VT     31/0600Z 50.0N  55.0W    50 KT...EXTRATROPICAL
120HR VT     01/0600Z 53.0N  40.0W    35 KT...EXTRATROPICAL
 
$$
FORECASTER BLAKE
 
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