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| #291362 (Received by flhurricane at: 11:14 AM 26.Aug.2009) TCDAT5 TROPICAL STORM DANNY DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL052009 1100 AM EDT WED AUG 26 2009 SATELLITE IMAGERY SHOWS THAT THE AREA OF DISTURBED WEATHER EAST OF THE BAHAMAS HAS DEVELOPED A WELL-DEFINED LOW-LEVEL CIRCULATION... WITH REPORTS FROM A NOAA HURRICANE HUNTER AIRCRAFT INDICATING THE SYSTEM WAS BEST DEVELOPED BELOW 12000 FT. QUIKSCAT DATA AND A FEW OBSERVATIONS FROM THE STEPPED FREQUENCY MICROWAVE RADIOMETER SHOW TROPICAL STORM-FORCE WINDS OCCURRING NORTH AND NORTHEAST OF THE CENTER...WHICH IS THE BASIS FOR THE INITIAL INTENSITY OF 40 KT. THE STORM HAS BEEN TANGLED UP WITH AN UPPER-LEVEL LOW FOR THE PAST 24 HR...AND THE STRUCTURE AS MUCH RESEMBLES A SUBTROPICAL CYCLONE AS A TROPICAL CYCLONE. HOWEVER...CYCLONE PHASE ANALYSES FROM FLORIDA STATE UNIVERSITY SUGGEST THAT DANNY IS MARGINALLY MORE TROPICAL THAN SUBTROPICAL...HENCE THE DESIGNATION OF TROPICAL STORM. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/16. DANNY IS ON THE NORTH SIDE OF A MID/UPPER-LEVEL LOW CENTERED OVER HISPANIOLA AND SOUTHWEST OF A MID/UPPER-LEVEL RIDGE CENTER EAST OF BERMUDA. THIS PATTERN SHOULD STEER DANNY GENERALLY NORTHWESTWARD WITH DECELERATION FOR THE NEXT 24-36 HR. AFTER THAT...THE LARGE SCALE MODELS AGREE THAT A MID/UPPER-LEVEL TROUGH SHOULD DEVELOP OVER THE GREAT LAKES...WITH A MID/UPPER-LEVEL LOW OVER THE GULF COAST STATES MOVING EASTWARD OR NORTHEASTWARD. THIS EVOLUTION SHOULD CAUSE DANNY TO TURN NORTHWARD AND THEN RECURVE INTO THE WESTERLIES. WHILE THE MODELS AGREE ON THE SCENARIO...THERE IS ENOUGH SPREAD IN THE TRACK GUIDANCE TO MAKE IT UNCERTAIN WHAT LAND AREA DANNY MAY AFFECT. THE NAM AND THE CANADIAN MODELS FORECAST DANNY TO MAKE LANDFALL IN EASTERN NORTH CAROLINA IN ABOUT 72 HR AND MOVE UP THE U. S. EASTERN SEABOARD...WHILE THE GFS...HWRF... AND GFDL SHOW A MORE EASTERLY TRACK THAT KEEPS DANNY OFFSHORE UNTIL IT REACHES THE CANADIAN MARITIMES. THE FORECAST SPLITS THE DIFFERENCE BETWEEN THESE EXTREMES AND IS A LITTLE TO THE LEFT OF THE MODEL CONSENSUS. THE FORECAST TRACK IS ROUGHLY PARALLEL TO THE U. S. EAST COAST...AND ANY DEVIATION FROM THE TRACK COULD MAKE A LARGE DIFFERENCE IN WHAT AREAS GET IMPACTED BY DANNY. THEREFORE...IT IS IMPORTANT NOT TO FOCUS TOO MUCH ON THE EXACT FORECAST TRACK. THE INTENSITY FORECAST IS PROBLEMATIC. WATER VAPOR IMAGERY SHOWS UPPER-LEVEL LOWS NORTH AND SOUTH OF DANNY CONNECTED BY A CYCLONIC SHEAR AXIS. THIS IS NOT A IDEAL PATTERN FOR STRENGTHENING...AND THE LARGE-SCALE MODELS SUGGEST IT MAY TAKE 24-36 HR FOR THE ENVIRONMENT TO BECOME MORE FAVORABLE. BASED ON THIS AND THE CURRENT ORGANIZATION OF THE STORM...THE INTENSITY FORECAST CALLS FOR SLOW STRENGTHENING FOR THE FIRST 36 HR. IT THEN SHOWS A FASTER STRENGTHENING FROM 36-48 HR AS CONDITIONS BECOME MORE FAVORABLE. AFTER 48 HR...STRONG UPPER-LEVEL SOUTHWESTERLY WINDS ASSOCIATED WITH THE EASTERN U. S. TROUGHS ARE EXPECTED TO CAUSE INCREASED SHEAR AND THE BEGINNING OF EXTRATROPICAL TRANSITION. THE INTENSITY FORECAST THUS CALLS FOR DANNY TO REACH 65 KT IN 72 HR...THEN BECOME EXTRATROPICAL BY 96 HR. THE INTENSITY FORECAST IS IN BEST AGREEMENT WITH THE SHIPS AND LGEM MODELS. HOWEVER...IT IS WEAKER THAN THE FORECASTS OF THE GFDL AND HWRF. FORECAST POSITIONS AND MAX WINDS INITIAL 26/1500Z 24.9N 70.3W 40 KT 12HR VT 27/0000Z 25.8N 72.0W 40 KT 24HR VT 27/1200Z 26.8N 73.6W 45 KT 36HR VT 28/0000Z 28.1N 74.5W 50 KT 48HR VT 28/1200Z 30.1N 75.2W 60 KT 72HR VT 29/1200Z 36.0N 73.5W 65 KT 96HR VT 30/1200Z 45.0N 67.0W 65 KT...EXTRATROPICAL 120HR VT 31/1200Z 52.0N 53.0W 60 KT...EXTRATROPICAL $$ FORECASTER BEVEN |
