471 
 WTNT45 KNHC 261512
 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