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| #355404 (Received by flhurricane at: 10:43 AM 27.Jun.2010) TCDAT1 TROPICAL DEPRESSION ALEX DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL012010 1000 AM CDT SUN JUN 27 2010 RECENT SATELLITE IMAGERY INDICATES THAT THE CONVECTIVE TOPS NEAR THE CENTER OF ALEX HAVE WARMED AND DECREASED IN COVERAGE OVER THE PAST FEW HOURS. BASED ON THESE TRENDS...AND A LACK OF ANY OBSERVATIONS OF STRONGER WINDS...THE INITIAL INTENSITY IS LOWERED TO 30 KT FOR THIS ADVISORY. THE INTENSITY FORECAST REASONING REMAINS UNCHANGED. AFTER ALEX EMERGES INTO THE GULF...WARM WATERS AND LOW SHEAR WILL OFFER THE OPPORTUNITY FOR RESTRENGTHENING. GIVEN THAT THE LOW-LEVEL CIRCULATION OF ALEX REMAINS WELL DEFINED...THE FORECAST CALLS FOR ALEX TO REGAIN TROPICAL STORM STATUS BY TONIGHT...AND FOR STEADY INTENSIFICATION THROUGH 72 HOURS. THE OFFICIAL FORECAST IS ABOVE ALL OF THE INTENSITY GUIDANCE THROUGH 48 HOURS...AND IS IN GOOD AGREEMENT WITH THE DECAY SHIPS MODEL BEYOND THAT TIME. NEEDLESS TO SAY...THE AMOUNT OF TIME THAT ALEX SPENDS OVER THE GULF WATERS WILL BE THE PIVOTAL FACTOR IN HOW MUCH INTENSIFICATION OCCURS. WHILE THE SHORT-TERM MOTION OF ALEX APPEARS ALMOST DUE WEST...A LONGER-TERM INITIAL MOTION ESTIMATE IS TOWARD THE WEST-NORTHWEST... 295 DEGREES AT 10 KNOTS....A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST TRACK. DURING THE FORECAST PERIOD...THE GLOBAL MODELS ARE IN GENERAL AGREEMENT WITH THE EVOLUTION OF THE LARGE-SCALE FLOW OVER NORTH AMERICA...WITH A LONGWAVE TROUGH DEVELOPING OVER THE EASTERN UNITED STATES IN TWO TO THREE DAYS...AND A MID- TO UPPER-LEVEL RIDGE DEVELOPING UPSTREAM OF THE TROUGH OVER CENTRAL NORTH AMERICA. HOWEVER...SUBTLE DIFFERENCES BETWEEN THE MODELS RESULT IN LARGE DIFFERENCES IN THE ULTIMATE TRACK OF ALEX. THE GFS...CANADIAN AND GFS ENSEMBLE MEAN ARE WEAKER WITH THE CENTRAL U.S. RIDGE IN 4 OR 5 DAYS. AS A RESULT...THESE MODELS HAVE BEEN PERSISTENTLY TAKING ALEX MORE POLEWARD. THE REMAINING MODELS SUGGEST THAT A STRONGER RIDGE NORTH OF ALEX WILL RESULT IN A MORE WESTWARD TURN LATE IN THE FORECAST PERIOD. THE ECMWF ENSEMBLE MEAN AND THE HWRF ARE ON THE NORTH SIDE OF THIS GROUP OF MODELS...BUT DO NOT SHOW A SHARP NORTHWARD TURN. ALL THAT BEING SAID...THE NEW OFFICIAL FORECAST IS ADJUSTED A LITTLE TO THE LEFT OF THE PREVIOUS ONE THROUGH 36 HOURS DUE TO THE INITIAL MOTION...AND BEYOND THAT TIME IS A LITTLE TO THE RIGHT OF THE PREVIOUS PACKAGE AND CLOSE TO THE TVCN MULTI-MODEL CONSENSUS. ALL OF THE MODEL UNCERTAINTY WITH THE TRACK OF ALEX OFFERS A REMINDER TO NOT TO FOCUS ON THE EXACT FORECAST TRACK...PARTICULARLY IN THE EXTENDED PART OF THE FORECAST PERIOD...WHERE AVERAGE FORECAST ERRORS CAN BE 200 TO 300 MILES. FORECAST POSITIONS AND MAX WINDS INITIAL 27/1500Z 18.7N 90.6W 30 KT 12HR VT 28/0000Z 19.6N 91.6W 35 KT...OVER WATER 24HR VT 28/1200Z 20.4N 92.6W 45 KT 36HR VT 29/0000Z 21.1N 93.4W 55 KT 48HR VT 29/1200Z 21.8N 94.2W 65 KT 72HR VT 30/1200Z 23.0N 96.0W 75 KT 96HR VT 01/1200Z 23.5N 98.0W 65 KT...INLAND 120HR VT 02/1200Z 24.0N 100.5W 30 KT...INLAND $$ FORECASTER BRENNAN |
