Official Discussion issued by the National Hurricane Center
FOUR (AL042010) DATA RELEASED: 8/2/2010 3:00:00 PM UTC
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Copy of official data 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 |