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| #287524 (Received by flhurricane at: 11:03 PM 11.Aug.2009) TCDAT2 TROPICAL DEPRESSION TWO DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009 1100 PM AST TUE AUG 11 2009 CONVENTIONAL SATELLITE IMAGERY INDICATES A RECENT BURST OF DEEP CONVECTION OVER THE WESTERN SEMICIRCLE OF THE DEPRESSION...WITH THE CENTER ON THE EASTERN EDGE OF THIS CONVECTIVE MASS. EVEN THOUGH DVORAK T-NUMBERS ARE 1.5 FROM BOTH TAFB AND SAB...A RECENTLY- RECEIVED ASCAT PASS FROM 0000 UTC SUPPORTS INCREASING THE INTENSITY TO 30 KT. EVEN MORE RECENTLY...LATEST SATELLITE IMAGERY SUGGESTS A FURTHER INCREASE IN ORGANIZATION AND THE DEPRESSION MAY NOW BE CLOSE TO TROPICAL STORM STRENGTH. WHILE THE CIRCULATION CENTER IS GRADUALLY BECOMING BETTER- DEFINED...THERE STILL EXISTS SOME UNCERTAINTY IN THE INITIAL LOCATION. THE INITIAL MOTION IS ESTIMATED TO BE 275/11...AS THE CYCLONE IS BEING STEERED BY DEEP-LAYER EASTERLY FLOW ON THE SOUTHERN PERIPHERY OF A MID-LEVEL SUBTROPICAL RIDGE. THIS PATTERN SHOULD FAVOR A GENERAL WEST TO WEST-NORTHWEST COURSE OVER THE NEXT SEVERAL DAYS...CONSISTENT WITH THE LATEST MODEL GUIDANCE. A WEAKNESS IN THE SUBTROPICAL RIDGE ON DAYS 4 AND 5 SHOULD ALLOW THE CYCLONE TO BEGIN GAINING MORE LATITUDE WITH AN INCREASE IN FORWARD SPEED. THE HWRF SOLUTION APPEARS TO BE AN OUTLIER AMONGST THE MODEL SUITE...IMMEDIATELY TAKING THE CYCLONE ON A MORE NORTHWESTWARD PATH. ON THE OTHER HAND...THE SPREAD OF THE REMAINING GUIDANCE IS RELATIVELY SMALL...EVEN IN THE LONGER RANGE...WHICH ADDS SOME CONFIDENCE TO THE CURRENT FORECAST. THE OFFICIAL FORECAST DISCOUNTS THE HWRF SOLUTION AND LIES BETWEEN THE MODEL CONSENSUS AND THE PREVIOUS ADVISORY. THE DEPRESSION IS CURRENTLY EMBEDDED IN A LOW SHEAR ENVIRONMENT WITH MARGINAL SEA SURFACE TEMPERATURES...WHICH SHOULD SUPPORT INTENSIFICATION. HOWEVER...SHIPS MODEL GUIDANCE INDICATES MODEST EASTERLY SHEAR IMPACTING THE CYCLONE SHORTLY THEREAFTER AS A RESULT OF INCREASING MID-LEVEL HEIGHTS TO THE NORTH. THIS INCREASE IN SHEAR SHOULD INHIBIT FURTHER DEVELOPMENT IN THE SHORT-TERM. LATER IN THE PERIOD...GLOBAL MODELS SUGGEST THAT THE CYCLONE WILL INTERACT WITH INCREASING SOUTHWESTERLY FLOW ALOFT...DOWNSTREAM OF A PRONOUNCED MID- TO UPPER-LEVEL CYCLONE WITHIN THE MID-OCEANIC TROUGH. THIS INTERACTION SHOULD INDUCE SUFFICIENT SHEAR TO WEAKEN THE SYSTEM BEGINNING DAY 4. SHOULD THE CYCLONE TAKE A MORE NORTHERLY TRACK...IT WOULD ENCOUNTER AN EVEN MORE HOSTILE ENVIRONMENT WHICH COULD ACCELERATE THE WEAKENING TREND. THEN AGAIN...SHOULD THE CYCLONE MAINTAIN A MORE SOUTHERN TRACK...THE SHEAR WOULD LIKELY BE LOWER WHICH WOULD SUPPORT A STRONGER SYSTEM. FORECAST POSITIONS AND MAX WINDS INITIAL 12/0300Z 14.8N 31.5W 30 KT 12HR VT 12/1200Z 14.8N 33.2W 35 KT 24HR VT 13/0000Z 14.8N 35.4W 35 KT 36HR VT 13/1200Z 14.9N 37.7W 35 KT 48HR VT 14/0000Z 15.2N 40.2W 40 KT 72HR VT 15/0000Z 16.5N 45.0W 45 KT 96HR VT 16/0000Z 19.0N 51.0W 45 KT 120HR VT 17/0000Z 22.0N 56.5W 40 KT $$ FORECASTER KIMBERLAIN/BROWN/COHEN |
