Tropical Storm SANDY

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TROPICAL STORM SANDY DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182012
500 AM EDT SAT OCT 27 2012
 
THE STRUCTURE OF SANDY HAS NOT CHANGED MUCH OVERNIGHT. THE CYCLONE
CONTINUES TO MAINTAIN AN AREA OF DEEP CONVECTION NEAR AND NORTHWEST
OF THE CENTER AND A DEEP WARM CORE. HOWEVER...DRY AIR AT THE MID
AND UPPER LEVEL IS FULLY ENTRAINED INTO THE EASTERN PORTION OF THE
CIRCULATION. THE CENTRAL PRESSURE REMAINS STEADY AROUND 969 MB...
BUT AIRCRAFT DATA SUGGEST THAT THE PEAK WINDS HAVE DECREASED TO
AROUND 60 KT WHILE THE CYCLONE CONTINUES TO GROW IN SIZE. THE
STRONGEST WINDS APPEAR TO BE LOCATED IN THE CONVECTIVE BAND WEST
AND NORTHWEST OF THE CENTER...WHERE RECENT SFMR AND DROPSONDE DATA
SHOWED A LARGE AREA OF WINDS AROUND 55 KT.
 
WHILE A LITTLE WEAKENING OF THE PEAK WINDS IS EXPECTED DURING THE
NEXT DAY OR SO...DIFFLUENCE ASSOCIATED WITH THE UPPER-LEVEL TROUGH
WEST OF SANDY SHOULD CONTINUE TO MAINTAIN A DEEP CENTRAL PRESSURE.
AS SANDY INTERACTS WITH A POTENT SHORTWAVE TROUGH IN A COUPLE OF
DAYS...THE GLOBAL MODELS SHOW THE CYCLONE STRENGTHENING DUE TO
BAROCLINIC FORCING WHILE THE WIND FIELD CONTINUES TO GROW IN SIZE.
THE NHC FORECAST SHOWS SANDY AGAIN REACHING HURRICANE STRENGTH AT
48 HOURS...WITH SOME ADDITIONAL DEEPENING POSSIBLE BEFORE LANDFALL
DURING EXTRATROPICAL TRANSITION. MODEL FIELDS SUGGEST THAT SANDY
WILL BE EXTRATROPICAL BY 72 HOURS AND THAT IS REFLECTED IN THE
OFFICIAL FORECAST.
 
SANDY HAS TURNED NORTH-NORTHEASTWARD WITH AN INITIAL MOTION OF
020/09. THE OVERALL TRACK FORECAST REASONING REMAINS UNCHANGED...AS
SANDY WILL ACCELERATE NORTHEASTWARD TODAY AND TONIGHT AHEAD OF A
DEEP-LAYER TROUGH MOVING INTO THE EASTERN UNITED STATES. A SHARP
NORTHWESTWARD TURN TOWARD THE U.S. EAST COAST IS EXPECTED AFTER 48
HOURS AS SANDY INTERACTS WITH THE AFOREMENTIONED SHORTWAVE MOVING
INTO THE CAROLINAS. NOT SURPRISINGLY...THERE REMAINS SOME SPREAD IN
THE GUIDANCE IN THE TIMING AND LOCATION OF LANDFALL...BUT THE MOST
NOTABLE TREND THIS CYCLE IS TOWARD A FASTER MOTION AS THE CYCLONE
TURNS NORTHWESTWARD. THE NHC FORECAST HAS BEEN TRENDED IN THAT
DIRECTION AND SHOWS THE CENTER INLAND AT 72 HOURS. OTHERWISE...THE
NEW NHC TRACK IS ALONG THE PREVIOUS ONE AND LIES ROUGHLY BETWEEN THE
ECMWF AND THE GFS THROUGH 72 HOURS.
 
REGARDLESS OF THE EXACT STRUCTURE AND LANDFALL LOCATION...SANDY IS
EXPECTED TO BE A LARGE AND POWERFUL CYCLONE WITH SIGNIFICANT
IMPACTS EXTENDING WELL AWAY FROM THE LOCATION OF THE CENTER.
 
NOTE THAT WIND HAZARDS FOR SANDY NORTH OF THE TROPICAL STORM WARNING
AREA ARE BEING HANDLED BY HIGH WIND...STORM...AND GALE WATCHES AND
WARNINGS ISSUED BY LOCAL NATIONAL WEATHER SERVICE OFFICES.
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0900Z 28.6N  76.7W   60 KT  70 MPH
 12H  27/1800Z 29.8N  75.8W   60 KT  70 MPH
 24H  28/0600Z 31.4N  74.2W   55 KT  65 MPH
 36H  28/1800Z 33.2N  72.5W   60 KT  70 MPH
 48H  29/0600Z 35.7N  71.6W   65 KT  75 MPH
 72H  30/0600Z 40.0N  75.5W   60 KT  70 MPH...POST-TROP/EXTRATROP
 96H  31/0600Z 41.5N  77.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  01/0600Z 43.5N  77.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
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FORECASTER BRENNAN
 
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