[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 021452
TCDAT4
TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042010
1100 AM EDT MON AUG 02 2010

DATA FROM AN 1148 UTC ASCAT PASS SUGGEST THAT THE DISTURBANCE IN THE
TROPICAL ATLANTIC NOW HAS A WELL-DEFINED SURFACE CIRCULATION...AND
ADVISORIES ARE INITIATED ON TROPICAL DEPRESSION FOUR.  THE INITIAL
INTENSITY IS SET AT 30 KT IN AGREEMENT WITH THE ASCAT DATA AND
DVORAK DATA T-NUMBERS OF 2.0 FROM TAFB AND SAB.

THE LOW-LEVEL CENTER APPEARS TO BE LOCATED ON THE SOUTHEASTERN EDGE
OF THE DEEP CONVECTION...AND IS MOVING RATHER BRISKLY TOWARD THE
WEST-NORTHWEST AT ABOUT 15 KT.  MUCH OF THE GUIDANCE SUGGESTS AN
EVEN FASTER MOTION IS LIKELY DURING THE NEXT COUPLE OF DAYS AS THE
DEPRESSION IS STEERED BY A STRONG SUBTROPICAL RIDGE TO ITS NORTH.
IN FOUR OR FIVE DAYS...THE GLOBAL MODELS SHOW A WEAKNESS DEVELOPING
IN THE RIDGE...WHICH SHOULD RESULT IN A TURN TOWARD THE NORTHWEST
WITH A DECREASE IN FORWARD SPEED.  THERE IS QUITE A BIT OF SPREAD
IN THE MODELS BY THE END OF THE PERIOD...WITH THE GFS ON THE LEFT
SIDE OF THE GUIDANCE SUITE AND THE HWRF AND ECMWF FARTHER RIGHT
SHOWING MORE RECURVATURE.  THE OFFICIAL FORECAST IS CLOSE TO THE
MULTI-MODEL TVCN CONSENSUS AND IN BEST AGREEMENT WITH THE GFDL.  IT
IS WORTH REMINDING USERS THAT THE AVERAGE ERROR OF THE OFFICIAL
TRACK FORECAST AT DAYS 4 AND 5 IS 250 TO 300 MILES.

THE ENVIRONMENT APPEARS FAVORABLE FOR SOME STRENGTHENING OVER THE
NEXT COUPLE OF DAYS...BUT AFTER THAT TIME VERTICAL WIND SHEAR IS
EXPECTED TO INCREASE AS THE CYCLONE APPROACHES AN UPPER-LEVEL
TROUGH AROUND 65W.  THE SHIPS MODEL SHOWS THE SHEAR INCREASING TO
AROUND 30 KT BY 72 HOURS...AND THE OFFICIAL FORECAST SHOWS A PEAK
IN INTENSITY AROUND THAT TIME...IN BEST AGREEMENT WITH THE ICON
INTENSITY CONSENSUS.  IF THE CYCLONE DOES NOT INTENSIFY IN THE NEXT
DAY OR SO...IT COULD STRUGGLE TO MAINTAIN A CLOSED SURFACE
CIRCULATION WITH SUCH A FAST FORWARD SPEED...AND COULD OPEN BACK UP
INTO A TROPICAL WAVE.

FORECAST POSITIONS AND MAX WINDS

INITIAL      02/1500Z 12.6N  41.1W    30 KT
 12HR VT     03/0000Z 13.5N  44.0W    35 KT
 24HR VT     03/1200Z 14.8N  48.9W    40 KT
 36HR VT     04/0000Z 16.4N  53.4W    45 KT
 48HR VT     04/1200Z 18.4N  57.4W    50 KT
 72HR VT     05/1200Z 22.0N  63.0W    50 KT
 96HR VT     06/1200Z 26.0N  66.5W    45 KT
120HR VT     07/1200Z 29.0N  68.5W    45 KT

$$
FORECASTER BRENNAN



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