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Tropical Storm Danny

TROPICAL STORM DANNY DISCUSSION NUMBER 2

Published on August 26, 2009 5:57 PM | Comments

This is looking like an east coast U.S. or Canadian storm as far as who has to worry - it is disorganized at the moment, but the forecast models do have it becoming a hurricane.

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.



Tropical Storm Danny 5 Day Cone

Published on August 26, 2009 5:45 PM | Comments



Tropical Storm Danny Open Thread

Published on August 26, 2009 5:41 PM | Comments

Tropical Storm Danny has formed north of the Caribbean region. This storm looks like it will track in between the Bahamas and Bermuda, just like Hurricane Bill did. Use this thread to discuss Danny.