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Tropical Depression FOUR


ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042006
1100 AM EDT TUE AUG 22 2006
 
DVORAK INTENSITY ESTIMATES AT 12Z WERE 30 KT FROM TAFB AND AFWA...
AND 35 KT FROM SAB.  SINCE THEN CONVECTION HAS DECAYED SOMEWHAT AND
SO THE ADVISORY INTENSITY WILL REMAIN 30 KT.  HIGHER VALUES IN THE
8Z QUIKSCAT PASS ARE BELIEVED TO BE RAIN CONTAMINATED.

THERE IS CLEAR ROTATION IN THE MID-LEVEL CLOUDS THAT COULD BE
REPRESENTATIVE OF THE SURFACE CENTER...BUT THE LOW CLOUD LINES
SUGGEST THE CENTER COULD BE DISPLACED A BIT TO THE SOUTHEAST.  THE
QUIKSCAT AMBIGUITIES SLIGHTLY FAVOR A DISPLACED CENTER.  SO WITH
SOME UNCERTAINTY...THE INITIAL MOTION IS ESTIMATED TO BE 295/14.  
GLOBAL MODEL GUIDANCE IS UNANIMOUS IN SHIFTING THE SUBTROPICAL RIDGE
EASTWARD WITH INCREASED MID- TO UPPER-LEVEL TROUGHING IN THE
CENTRAL ATLANTIC OVER THE NEXT SEVERAL DAYS.  THIS SHOULD ALLOW THE
DEPRESSION TO MAINTAIN ITS PRESENT WEST-NORTHWESTWARD HEADING FOR
AT LEAST THE NEXT THREE DAYS.  AFTER THAT...THERE SEEM TO BE TWO
PRIMARY OPTIONS.  THERE IS GOOD AGREEMENT IN THE GLOBAL MODELS THAT
THE CYCLONE WILL ENCOUNTER INCREASED SOUTHERLY SHEAR.  THIS COULD
TURN THE CYCLONE NORTHWARD...IF THE SYSTEM CAN HANG TOGETHER. 
ALTERNATIVELY...THE SYSTEM COULD SHEAR OFF AND THE WEAKENED
REMNANTS TURN WESTWARD.  THE FORMER SCENARIO IS FAVORED BY THE GFS
AND GFDL...WHILE THE LATTER SCENARIO IS THE CHOICE OF THE UKMET AND
ECMWF MODELS.   FOR NOW...I'VE MADE NO CHANGES TO THE PREVIOUS
ADVISORY TRACK...WHICH SPLITS THE DIFFERENCE.

THERE IS A LOT OF STABLE AIR IN THE ENVIRONMENT AHEAD OF THE
DEPRESSION.  NEVERTHELESS...BOTH THE SHIPS AND GFDL GUIDANCE
INDICATE STRENGTHENING TO AT LEAST A STRONG TROPICAL STORM.  GIVEN
THAT THE DEPRESSION HAS NOT STRENGTHENED YET OVER THE WARMEST
WATERS IT WILL SEE FOR THE NEXT FOUR DAYS...I WONDER IF THE
GUIDANCE IS A LITTLE TOO AGGRESSIVE.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/1500Z 13.6N  26.1W    30 KT
 12HR VT     23/0000Z 14.6N  28.1W    35 KT
 24HR VT     23/1200Z 16.1N  30.7W    40 KT
 36HR VT     24/0000Z 17.6N  33.4W    45 KT
 48HR VT     24/1200Z 19.2N  36.3W    50 KT
 72HR VT     25/1200Z 22.0N  42.5W    60 KT
 96HR VT     26/1200Z 25.0N  48.0W    65 KT
120HR VT     27/1200Z 28.0N  53.0W    65 KT
 
$$
FORECASTER FRANKLIN
 
NNNN


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Page last modified: Monday, 11-Sep-2006 11:28:35 UTC