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Hurricane SANDY


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HURRICANE SANDY DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182012
1100 PM EDT THU OCT 25 2012

REPORTS FROM A NOAA HURRICANE HUNTER AIRCRAFT INDICATE THAT SANDY
HAS WEAKENED A LITTLE THIS EVENING.  THE MAXIMUM FLIGHT-LEVEL WINDS
AT 8000 FT WERE 90 KT...AND DROPSONDES IN WHAT REMAINED OF THE
EYEWALL SUGGESTED 70 KT SURFACE WINDS.  THE CENTRAL PRESSURE HAD
RISEN TO 968 MB.  BASED ON THESE DATA...THE INITIAL INTENSITY IS
REDUCED TO 80 KT...AND THIS COULD BE A LITTLE GENEROUS.  SURFACE
OBSERVATIONS INDICATE THAT THE OUTER WIND FIELD CONTINUES TO
EXPAND...ESPECIALLY IN THE NORTHERN SEMICIRCLE.

SANDY HAS BEGUN ITS ANTICIPATED LEFT TURN AND THE INITIAL MOTION IS
NOW 335/11.  THE HURRICANE SHOULD CONTINUE A GENERAL NORTH-
NORTHWESTWARD MOTION FOR THE NEXT 24 HOURS OR SO AS IT INTERACTS
WITH A MID/UPPER-LEVEL LOW OVER THE FLORIDA STRAITS.  AFTER
THAT...A DEEP-LAYER LONGWAVE TROUGH MOVING INTO THE EASTERN UNITED
STATES SHOULD CAUSE SANDY TO TURN NORTHWARD AND NORTHEASTWARD. 
AFTER 72 HR...SANDY SHOULD INTERACT WITH A SHORTWAVE TROUGH MOVING
THROUGH THE LARGER LONGWAVE...WHICH IS EXPECTED TO TURN THE CYCLONE
BACK TOWARD THE NORTHWEST...A TRACK THAT SHOULD BRING THE CENTER
ONSHORE IN THE NORTHEASTERN UNITED STATES.  THE GUIDANCE IS IN FAIR
TO GOOD AGREEMENT ON THIS...AND THERE HAS BEEN NO SIGNIFICANT
CHANGE IN THE GUIDANCE SINCE THE LAST ADVISORY.  THE NEW FORECAST
TRACK IS SIMILAR TO THE PREVIOUS TRACK...EXCEPT FOR A LITTLE MORE
WESTWARD POSITION AT THE 24 HOUR POINT THAT LIES BETWEEN THE GFS
AND ECMWF MODELS ON THE LEFT SIDE OF THE TRACK GUIDANCE ENVELOPE. 
OTHERWISE...THE TRACK IS NEAR THE CENTER OF THE GUIDANCE ENVELOPE.

WATER VAPOR IMAGERY SHOWS THE UPPER-LEVEL TROUGH IS PRODUCING STRONG
UPPER-LEVEL DIVERGENCE OVER AND NEAR SANDY...WHICH IS HELPING TO
KEEP THE STORM GOING DESPITE 35 KT OF VERTICAL WIND SHEAR.  THE
RESULT OF THIS INTERACTION IS THAT SANDY SHOULD CONTINUE TO EXPAND
IN SIZE...WITH A GRADUAL REDUCTION IN THE CENTRAL WINDS.  LATER IN
THE FORECAST PERIOD...INTERACTION WITH THE SHORTWAVE TROUGH IS
EXPECTED TO CAUSE SOME RE-INTENSIFICATION AS THE CYCLONE STARTS
EXTRATROPICAL TRANSITION.  THIS PROCESS IS LIKELY TO BEGIN AS EARLY
AS 96 HR...BUT IT IS UNCLEAR JUST HOW FAR IT WILL HAVE PROCEEDED
BEFORE THE CYCLONE MAKES LANDFALL.  THUS...THE FORECAST CONTINUES
TO CALL FOR THE SYSTEM TO BE POST-TROPICAL IN 120 HR...WITH A VERY
LOW CONFIDENCE.  THE NEW INTENSITY FORECAST IS SIMILAR TO THE
PREVIOUS ADVISORY...WITH SOME MODIFICATION TO THE FIRST 36 HR DUE
TO THE OBSERVED WEAKENING THIS EVENING.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0300Z 25.3N  76.1W   80 KT  90 MPH
 12H  26/1200Z 26.6N  76.8W   75 KT  85 MPH
 24H  27/0000Z 27.6N  77.4W   75 KT  85 MPH
 36H  27/1200Z 28.9N  76.9W   70 KT  80 MPH
 48H  28/0000Z 30.4N  75.4W   65 KT  75 MPH
 72H  29/0000Z 34.0N  72.5W   70 KT  80 MPH
 96H  30/0000Z 37.5N  72.5W   70 KT  80 MPH
120H  31/0000Z 40.5N  76.5W   55 KT  65 MPH...INLAND POST-TROPICAL
 
$$
FORECASTER BEVEN
 
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