000
WTNT45 KNHC 262035
TCDAT5
TROPICAL STORM DANNY DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL052009
500 PM EDT WED AUG 26 2009
 
SATELLITE IMAGERY AND REPORTS FROM AN AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT INDICATE THAT DANNY IS VERY DISORGANIZED AT THIS
TIME.  THERE IS NO ORGANIZED CONVECTION NEAR THE CENTER...AND THE
STRONGEST WINDS ARE IN A BAND 100-150 N MI FROM THE CENTER OVER THE
NORTHERN SEMICIRCLE.  THE AIRCRAFT REPORTED 1500 FT FLIGHT-LEVEL
WINDS OF 49 KT AND ESTIMATED SURFACE WINDS OF 40-45 KT FROM THE
SFMR.  BASED ON THIS...THE INITIAL INTENSITY REMAINS 40 KT.  THE
AIRCRAFT JUST REPORTED A CENTRAL PRESSURE OF 1007 MB.
 
THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 300/10...UNCERTAIN
BECAUSE THE STORM SEEMS TO BE DECELERATING...AND THE CENTER MAY BE
OCCASIONALLY RE-FORMING DUE TO CONVECTIVE BURSTS.  THERE IS NO
CHANGE TO THE PREVIOUS FORECAST REASONING.  DANNY IS NORTH 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 FOR THE NEXT 24 HR OR SO. 
AFTER 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 STILL SIGNIFICANT
UNCERTAINTY AS TO WHAT LAND AREA DANNY MAY AFFECT.  THE ECMWF...
UKMET...AND CANADIAN MODELS FORECAST THE CENTER TO PASS NEAR CAPE
HATTERAS AND THEN MAKE LANDFALL IN NEW ENGLAND.  THE GFS AND GFDL
SHOW THE CENTER PASSING EAST OF HATTERAS AND THEN PASSING NEAR OR
OVER CAPE COD.  THE HWRF AND NOGAPS...AS WELL AS THE CORRECTED
CONSENSUS MODELS...SHOW THE CENTER PASSING EAST OF CAPE COD AND
NEAR OR OVER NOVA SCOTIA.  OVERALL..THE GUIDANCE ENVELOPE HAS
SHIFTED SLIGHTLY TO THE EAST SINCE THE LAST ADVISORY.  THE NEW
FORECAST TRACK IS ALSO SHIFTED SLIGHTLY TO THE EAST AND LIES NEAR
THE MIDDLE OF THE GUIDANCE ENVELOPE.  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 REMAINS 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 IT MAY TAKE 24 HR OR MORE FOR THE ENVIRONMENT
TO BECOME MORE FAVORABLE.  IN ADDITION...THE CURRENT STRUCTURE OF
THE STORM FAVORS SLOW STRENGTHENING AT BEST.  BASED ON THIS...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 INITIATE EXTRATROPICAL
TRANSITION...WHICH COULD START BEFORE DANNY REACHES THE LATITUDE OF
NEW ENGLAND.  THE INTENSITY FORECAST 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 REMAINS WEAKER THAN THE FORECASTS OF THE GFDL AND
HWRF.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/2100Z 25.2N  71.2W    40 KT
 12HR VT     27/0600Z 26.0N  72.5W    40 KT
 24HR VT     27/1800Z 27.1N  73.8W    45 KT
 36HR VT     28/0600Z 28.7N  74.5W    50 KT
 48HR VT     28/1800Z 31.1N  74.5W    60 KT
 72HR VT     29/1800Z 38.5N  71.5W    65 KT
 96HR VT     30/1800Z 47.5N  63.5W    60 KT...EXTRATROPICAL
120HR VT     31/1800Z 53.1N  48.0W    45 KT...EXTRATROPICAL
 
$$
FORECASTER BEVEN