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Tropical Depression TWO


ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION TWO DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022009
500 PM AST WED AUG 12 2009

THE DEPRESSION APPEARED TO BE ON THE VERGE OF BECOMING A TROPICAL
STORM A FEW HOURS AGO...WITH SATELLITE INTENSITY ESTIMATES OF 35 KT
FROM TAFB AND SAB.  HOWEVER...SINCE ABOUT 18Z THE CONVECTION HAS
DECREASED SIGNIFICANTLY AND HAS MOVED FARTHER AWAY FROM THE EXPOSED
LOW-LEVEL CENTER.  BASED ON THIS...THE CYCLONE WILL REMAIN A 30 KT
DEPRESSION FOR THIS ADVISORY.  THE CURRENT DOWNWARD TREND IN THE
CONVECTION MAY BE DUE TO AN INCREASE IN EASTERLY VERTICAL WIND
SHEAR...AND TO A DRY SLOT WRAPPING AROUND THE CIRCULATION NOTED IN
AMSR-E VAPOR IMAGERY NEAR 1534Z.  ALSO...AS SEEN EARLIER...MOST OF
THE LOW-LEVEL INFLOW INTO THE DEPRESSION SEEMS TO BE COMING FROM
THE NORTH...REPRESENTING POSSIBLY MORE STABLE AIR PASSING OVER
COOLER WATERS.  THE FLOW ON THE SOUTH SIDE OF THE DEPRESSION IS
FEEDING INTO A LARGE DISTURBANCE BETWEEN THE CAPE VERDE ISLANDS AND
AFRICA.
 
THE INITIAL MOTION IS 265/12.  THE DEPRESSION IS ON THE SOUTH
SIDE OF A LARGE LOW/MID-LEVEL RIDGE...AND THE LARGE-SCALE MODELS
FORECAST THIS TO CONTINUE FOR THE NEXT TWO DAYS OR SO.  AFTER THAT
TIME...THE MODELS FORECAST A WEAKNESS IN THE RIDGE THAT WOULD STEER
THE CYCLONE WEST-NORTHWESTWARD.  THE TRACK MODEL GUIDANCE GENERALLY
AGREES WITH THIS SCENARIO...AND WHILE THE MODEL CLUSTERS SEEN
EARLIER HAVE MERGED THERE IS STILL A SIGNIFICANT SPREAD BY 120 HR.
THE GFS AND UKMET ARE ON THE SOUTH SIDE OF THE GUIDANCE ENVELOPE
SHOWING A MORE WESTERLY MOTION...WHILE THE HWRF AND BAMD ARE ON THE
NORTH SIDE SHOWING A NORTHWESTWARD MOTION BY 120 HR.  OVERALL...THE
GUIDANCE ENVELOPE HAS AGAIN SHIFTED A LITTLE SOUTHWARD...AND SO HAS
THE NEW OFFICIAL FORECAST.  THE NEW TRACK IS IN THE CENTER OF THE
GUIDANCE ENVELOPE IN BEST AGREEMENT WITH THE TVCN AND TVCC
CONSENSUS MODELS.
 
THE DEPRESSION REMAINS OVER SEA SURFACE TEMPERATURES NEAR 27C...WITH
SSTS ALONG THE FORECAST TRACK INCREASING TO 28C AFTER 72 HR.  THE
LARGE-SCALE MODELS FORECAST THE DEPRESSION TO ENCOUNTER MODERATE
VERTICAL WIND SHEAR DURING THE FORECAST PERIOD...FIRST FROM THE
EAST AND LATER FROM THE SOUTHWEST.  ALSO...WATER VAPOR IMAGERY
SHOWS VERY DRY AIR AT THE MID/UPPER-LEVELS TO THE NORTHWEST OF THE
DEPRESSION.  THE LATTER TWO FACTORS SUGGEST THE SYSTEM MAY BE SLOW
TO STRENGTHEN...AND NONE OF THE INTENSITY GUIDANCE CURRENTLY
FORECASTS AN INTENSITY GREATER THAN 55 KT DURING THE FORECAST
PERIOD.  BASED ON THIS...THE NEW INTENSITY FORECAST IS AN UPDATE OF
THE PREVIOUS FORECAST IN BEST AGREEMENT WITH THE SHIPS MODEL.  IT
IS POSSIBLE THAT THE SYSTEM COULD WEAKEN TO A TROPICAL WAVE DURING
THE FORECAST PERIOD...AS FORECAST BY THE ECMWF...UKMET...AND GFS
MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/2100Z 14.3N  35.0W    30 KT
 12HR VT     13/0600Z 14.1N  36.7W    35 KT
 24HR VT     13/1800Z 14.1N  38.9W    35 KT
 36HR VT     14/0600Z 14.2N  41.3W    40 KT
 48HR VT     14/1800Z 14.6N  43.7W    45 KT
 72HR VT     15/1800Z 16.0N  49.5W    50 KT
 96HR VT     16/1800Z 19.0N  56.0W    50 KT
120HR VT     17/1800Z 23.0N  62.0W    45 KT
 
$$
FORECASTER BEVEN
 
NNNN


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Page last modified: Thursday, 31-Dec-2009 12:09:03 UTC