[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 010250
TCDAT3
TROPICAL DEPRESSION THREE DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032006
1100 PM EDT MON JUL 31 2006

REPORTS FROM FRENCH BUOY 41100 LATE THIS AFTERNOON INDICATED THAT
THERE WAS A WEAK CIRCULATION ASSOCIATED WITH THE TROPICAL WAVE
APPROACHING THE LESSER ANTILLES.  A QUIKSCAT PASS AT 21Z CONFIRMED
THAT THE CIRCULATION EXISTED BUT ALSO INDICATED THAT THE
CIRCULATION WAS VERY SMALL.  OVER THE PAST SEVERAL HOURS...THE
SYSTEM HAS BEEN MAINTAINING ENOUGH DEEP CONVECTION TO BE CONSIDERED
A TROPICAL DEPRESSION.  THE INITIAL INTENSITY IS SET TO 30 KT BASED
ON THE QUIKSCAT DATA AND THE DVORAK CLASSIFICATIONS FROM TAFB AND
SAB.

THE CENTER OF THE DEPRESSION IS LOCATED NEAR THE WESTERN EDGE OF THE
CONVECTIVE MASS...DUE TO WESTERLY SHEAR RESULTING PRIMARILY FROM
STRONG EASTERLIES IN THE LOWER TROPOSPHERE.  THE UPPER ENVIRONMENT
AHEAD OF THE DEPRESSION IS COMPLICATED...AND THE EVOLUTION OF A
LARGE UPPER-LOW JUST EAST OF THE BAHAMAS WILL BE IMPORTANT TO THE
FUTURE OF THE DEPRESSION.  SOME GUIDANCE...PARTICULARLY THE
UKMET...SUGGESTS THAT THIS UPPER LOW WILL KEEP A STRONG WESTERLY
SHEARING FLOW IN PLACE IN THE PATH OF THE DEPRESSION.  OTHER GLOBAL
MODELS RELAX THIS FLOW...BUT IT MAY NOT MATTER MUCH...AS THE SYSTEM
CONTINUES TO DEAL WITH A VERY DRY AIR MASS.  THE GFDL MODEL
DISSIPATES THE SYSTEM...AS DO ALL OF THE GLOBAL MODELS.  THE SHIPS
MODEL SHOWS A VERY SLOW DEVELOPMENT TREND...BUT PERHAPS THIS MODEL
CANNOT APPRECIATE JUST HOW FRAGILE A SYSTEM THE DEPRESSION IS RIGHT
NOW.  THE OFFICIAL FORECAST FOLLOWS THE GLOBAL MODEL GUIDANCE THAT
SUGGESTS THIS CYCLONE MAY BE SHORT LIVED.

THE INITIAL MOTION IS 295/14.  THE DOMINANT STEERING IS EXPECTED TO
BE PROVIDED BY THE MID- TO LOWER-TROPOSPHERIC FLOW.  THE DEPRESSION
IS THEREFORE EXPECTED TO CONTINUE GENERALLY TO THE WEST-NORTHWEST
TO THE SOUTH OF THE SUBTROPICAL RIDGE...WITH SOME REDUCTION IN
FORWARD SPEED DUE TO A WEAKNESS IN THE RIDGE ASSOCIATED WITH THE
AFOREMENTIONED UPPER-LOW.  THE OFFICIAL FORECAST IS IN GOOD
AGREEMENT WITH THE SHALLOW BAM.

FORECAST POSITIONS AND MAX WINDS

INITIAL      01/0300Z 16.6N  59.4W    30 KT
 12HR VT     01/1200Z 17.4N  61.2W    30 KT
 24HR VT     02/0000Z 18.3N  63.4W    30 KT
 36HR VT     02/1200Z 19.2N  65.5W    30 KT
 48HR VT     03/0000Z 20.1N  67.7W    30 KT
 72HR VT     04/0000Z 21.5N  71.5W    25 KT...DISSIPATING
 96HR VT     05/0000Z...DISSIPATED

$$
FORECASTER FRANKLIN

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