ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM DARBY DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 PM PDT TUE JUL 27 2004 DARBY APPEARS TO BE VERY CLOSE TO HURRICANE STRENGTH. ALTHOUGH THE EARLIER BANDING EYE-LIKE FEATURE HAS DISAPPEARED...SUBJECTIVE CLASSIFICATIONS FROM TAFB AND SAB AT 0Z WERE BOTH T4.0...65 KT. AFWA'S ESTIMATE WAS LOWER...AT 55 KT...AND THE MOST RECENT OBJECTIVE DVORAK NUMBERS FROM UW/CIMSS ARE ALSO BELOW HURRICANE STRENGTH. CONSEQUENTLY DARBY IS BEING HELD AS A TROPICAL STORM FOR THIS ADVISORY. ALTHOUGH DARBY WILL REMAIN IN A WARM WATER/LOW SHEAR ENVIRONMENT FOR THE NEXT 24-36 HOURS...NEITHER THE GFDL NOR THE SHIPS GUIDANCE IS CALLING FOR MORE THAN ABOUT 10 KT OF ADDITIONAL STRENGTHENING. THE SHIPS GUIDANCE IN PARTICULAR IS SUGGESTING THAT THE THERMODYNAMIC ENVIRONMENT AHEAD OF DARBY WILL BE INCREASINGLY HOSTILE. LATE IN THE FORECAST PERIOD...COOLER WATERS AND INCREASING WESTERLY SHEAR ARE EXPECTED TO WEAKEN THE CYCLONE. THE OFFICIAL FORECAST IS VERY CLOSE TO THE SHIPS AND GFDL GUIDANCE. DARBY IS MOVING AT 290/13. MODEL GUIDANCE IS IN PRETTY GOOD AGREEMENT ON A CONTINUATION OF THIS TRACK THROUGH 36 HOURS AS DARBY MOVES AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE. IN A COUPLE OF DAYS...DARBY SHOULD BE SOUTH OF A WEAKNESS IN THE RIDGE THAT MAY CAUSE THE FORWARD SPEED TO SLOW...AND THIS IS REFLECTED IN THE OFFICIAL FORECAST. AFTER THAT TIME...THE WEAKENING CYCLONE IS EXPECTED TO TURN TO A SLIGHTLY MORE WESTERLY TRACK. THE GFS IS SOMETHING OF AN OUTLIER...CALLING FOR A RAPID WEAKENING OF DARBY FOLLOWED BY A RATHER QUICK TURN TO THE WEST. THE OFFICIAL FORECAST IS DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE AND IN BEST AGREEMENT WITH THE UKMET. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 28/0300Z 14.4N 121.2W 60 KT 12HR VT 28/1200Z 15.1N 122.9W 70 KT 24HR VT 29/0000Z 15.7N 125.0W 75 KT 36HR VT 29/1200Z 16.4N 127.1W 75 KT 48HR VT 30/0000Z 17.0N 129.0W 70 KT 72HR VT 31/0000Z 17.5N 133.0W 65 KT 96HR VT 01/0000Z 18.0N 137.5W 55 KT 120HR VT 02/0000Z 18.5N 142.0W 45 KT $$ NNNN
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Page last modified: Wednesday, 28-Jul-2004 02:42:26 UTC