Tropical Storm DEBBY

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TROPICAL STORM DEBBY DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042012
1000 PM CDT SAT JUN 23 2012
 
DEBBY IS GRADUALLY SHOWING SIGNS OF IMPROVED ORGANIZATION AS THE
UPPER-LEVEL SHEAR SHIFTS FROM SOUTHWESTERLY TO MORE OF A SOUTHERLY
COMPONENT. SHIP ZCDJ2 LOCATED ABOUT 80 NMI EAST OF THE CENTER AND
NEAR NOAA BUOY 42003 REPORTED A PRESSURE OF 1001.6 MB AND 38 KT
WINDS AT 24/00Z. BASED ON THIS INFORMATION...THE CENTRAL PRESSURE
IS CONSERVATIVELY ESTIMATED TO BE 998 MB. AIRCRAFT RECONNAISSANCE
DATA AT 23/2020Z INDICATED 850 MB FLIGHT-LEVEL WINDS OF 61 KT IN
THE NORTHEAST QUADRANT...WHICH IS EQUAL TO ABOUT 49 KT SURFACE
WINDS. CONVECTION WAS SOMEWHAT MEAGER AT THAT...BUT SINCE THEN HAS
INCREASED RATHER MARKEDLY IN THAT AREA. THEREFORE THE INITIAL
INTENSITY ESTIMATE IS A SOLID 45 KT.

DEBBY HAS BEEN NEARLY STATIONARY DURING THE PAST 6 HOURS. MULTIPLE
LOW-LEVEL VORTICES HAVE BEEN OUT FROM UNDERNEATH THE EASTERN
SEMICIRCLE CONVECTIVE CLOUD MASS ABOUT A MEAN CENTER OF ROTATION OF
A LARGER GYRE...AND THE LOCATION OF THE LARGER STATIONARY GYRE IS
THE ADVISORY POSITION. ALTHOUGH THERE MAY BE SOME SLIGHT
NORTHEASTWARD MOTION DUE TO REDEVELOPMENT OF THE CENTER CLOSER TO
THE DEEP CONVECTION...THE GENERAL MOTION FOR THE NEXT 24 HOURS OR
SO SHOULD BE SLOWLY POLEWARD. THE LONGWAVE PATTERN ACROSS THE U.S.
HAS A DEEPENING TROUGH OFF THE WEST COAST...WHICH IS CREATING
DOWNSTREAM RIDGING ACROSS THE CENTRAL AND EASTERN UNITED STATES.
THIS INCREASED RIDGING IS REFLECTED BY 20-40 METER 500 MB HEIGHT
RISES AT 00Z ACROSS THE CENTRAL AND SOUTHERN PLAINS...AND EXTENDING
AS FAR EAST AS THE CAROLINA COASTS. THIS BLOCKING RIDGE PATTERN TO
THE NORTH OF DEBBY IS EXPECTED TO GRADUALLY TURN THE CYCLONE
WESTWARD ACROSS THE NORTH-CENTRAL GULF OF MEXICO BY 36-48
HOURS...WITH A CONTINUED WESTWARD MOTION ACROSS THE NORTHWESTERN
GULF AFTER THAT. ALL OF THE AVAILABLE NHC MODEL GUIDANCE...EXCEPT
FOR THE GFS AND GFS-ENSEMBLE MODELS...SUPPORTS THE GENERAL WESTWARD
MOTION SCENARIO. THE MAIN REASON THAT THE GFS MOVES DEBBY EASTWARD
ACROSS THE NORTHEASTERN GULF IS DUE TO IT HAVING A WEAKER AND MORE
VERTICALLY SHALLOW STORM DEPICTED IN THE MODEL. GIVEN THE EXPECTED
FAVORABLE UPPER-LEVEL FLOW PATTERN WITH WEAKER VERTICAL SHEAR
FORECAST TO DEVELOP AFTER 24 HOURS...A DEEPER AND MORE ROBUST
WESTWARD MOVING TROPICAL CYCLONE AS DEPICTED IN THE
ECMWF...UKMET... NOGAPS MODELS SEEMS A MORE REASONABLE SCENARIO.
THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS
ADVISORY TRACK.

MODERATE SOUTHWESTERLY VERTICAL WIND SHEAR IS EXPECTED TO GRADUALLY
GIVE WAY TO SOUTHERLY AND EVENTUALLY SOUTHEASTERLY WEAKER WIND
SHEAR BY 36-48 HOURS AS AN UPPER-LEVEL LOW NORTHWEST OF THE CYCLONE
MOVES SOUTHWESTWARD...WHICH ALLOWS DEBBY TO MOVE UNDERNEATH A 200
MB RIDGE AXIS. THE OFFICIAL INTENSITY FORECAST LEANS TOWARD THE
ECMWF MODEL...WHICH IS FORECASTING A HURRICANE CENTRAL PRESSURE BY
96 HOURS...AND IS ABOVE THE GFS-BASED SHIPS AND LGEM MODELS SINCE
THAT OUTPUT LIKELY DOES NOT REPRESENT THE ENVIRONMENTAL CONDITIONS
THAT DEBBY WILL ENCOUNTER. THE OFFICIAL INTENSITY FORECAST IS A
LITTLE HIGHER THAN THE PREVIOUS ADVISORY...AND BRINGS DEBBY TO
HURRICANE STRENGTH BY 72 HOURS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/0300Z 26.3N  87.5W   45 KT  50 MPH
 12H  24/1200Z 26.7N  87.8W   50 KT  60 MPH
 24H  25/0000Z 27.0N  88.1W   50 KT  60 MPH
 36H  25/1200Z 27.1N  88.8W   55 KT  65 MPH
 48H  26/0000Z 27.2N  89.8W   60 KT  70 MPH
 72H  27/0000Z 27.2N  91.8W   65 KT  75 MPH
 96H  28/0000Z 27.2N  93.7W   70 KT  80 MPH
120H  29/0000Z 27.2N  95.2W   70 KT  80 MPH
 
$$
FORECASTER STEWART
 
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