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Hurricane SANDY


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
 
HURRICANE SANDY DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182012
500 AM EDT THU OCT 25 2012
 
EARLIER THIS MORNING...SANDY MADE LANDFALL JUST WEST OF SANTIAGO DE
CUBA AS A STRONG CATEGORY TWO HURRICANE. CUBAN RADAR DATA AND
REPORTS FROM AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT INDICATED
THAT SANDY HAD A WELL-DEFINED 20-24 N MI DIAMETER EYE WHEN IT MADE
LANDFALL. THE AIRCRAFT REPORTED MAXIMUM 700-MB FLIGHT-LEVEL WINDS
OF 117 KT AND BIAS-CORRECTED SFMR SURFACE ESTIMATES OF 91-92 KT. A
BLEND OF THESE DATA YIELDS A SURFACE WIND ESTIMATE OF 99 KT...JUST
BELOW MAJOR HURRICANE STATUS. THE MAIN REASON WHY SANDY WAS HELD
JUST BELOW MAJOR HURRICANE STATUS WAS DUE TO THE SUSTAINED 68-KT
WIND AND GUST TO 99 KT THAT OCCURRED AROUND 0517Z. HOWEVER...
STRONGER WINDS MAY HAVE OCCURRED LATER WHEN THE SOUTHEASTERN
PORTION OF THE EYEWALL MOVED ONSHORE...WHICH IS THE QUADRANT WHERE
THE 117-KT FLIGHT-LEVEL WIND WAS OBSERVED. THE INITIAL INTENSITY OF
90 KT IS BASED ON WIND DECAY MODELS FOR HURRICANES OVER LAND.

THE INITIAL MOTION IS 005/16 KT. AFTER A SLIGHT JOG TO THE
NORTH-NORTHEAST VERY EARLY THIS MORNING...SANDY APPEARS TO HAVE
RESUMED A NORTHWARD MOTION...AND THIS GENERAL MOTION IS EXPECTED TO
CONTINUE FOR THE NEXT 24 HOURS OR SO. AFTER THAT...A DEEP-LAYER
TROUGH OVER THE NORTHERN U.S. AND A SIMILAR DEEP-LAYER TROUGH OVER
THE NORTH ATLANTIC EAST OF NEWFOUNDLAND ARE FORECAST TO AMPLIFY...
WHICH WILL INDUCE MID-LEVEL RIDGING NEAR THE NORTHEAST U.S. COAST
BETWEEN THOSE TWO SYSTEMS. THAT RIDGE IS EXPECTED TO CAUSE SANDY TO
SLOW DOWN AND TURN TOWARD THE NORTH-NORTHWEST IN 24-36 HOURS. AFTER
THAT...THE RIDGE TO THE NORTH OF SANDY IS FORECAST TO WEAKEN AS AN
APPROACHING DEEP MID-LATITUDE TROUGH MOVES OVER THE EASTERN HALF OF
THE UNITED STATES BY 72 HOURS AND BEGINS TO ACCELERATE SANDY TO THE
NORTHEAST. THE NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS
DEVELOPING SCENARIO. AFTER THAT...HOWEVER...THE GUIDANCE DIVERGES
SIGNIFICANTLY WITH THE ECMWF...GFDL...AND NOGAPS TAKING SANDY
NORTHWESTWARD AND INLAND OVER THE DELMARVA PENINSULA BY 120
HOURS...WHEREAS THE GFS MODEL KEEPS SANDY MOVING NORTHEASTWARD AWAY
FROM THE U.S. AND OVER THE OPEN NORTH ATLANTIC. THE REMAINDER OF
THE MODEL GUIDANCE IS SOMEWHERE IN BETWEEN THESE TWO EXTREMES.
GIVEN THE HISTORICAL RELIABILITY OF THE VERY CONSISTENT ECMWF MODEL
OVER THE PAST 2 DAYS...THE OFFICIAL FORECAST WAS TURNED SLIGHTLY
MORE TOWARD THE NORTHWEST AT 120 HOURS...AND IS CLOSE TO A BLEND OF
THE CONSENSUS MODELS TV15 AND TVCN...AND THE FSU TRACK MODEL.

OWING TO THE HIGHER CURRENT INTENSITY OF SANDY...THE NEW INTENSITY
FORECAST IS ALSO HIGHER THAN THE PREVIOUS FORECAST THROUGH 36
HOURS...AND THEN IS SIMILAR TO THE PREVIOUS ADVISORY INTENSITY
FORECAST AS INCREASING SHEAR BEGINS TO AFFECT THE CYCLONE. THE MAIN
FORECAST CHALLENGE IS DETERMINING JUST HOW MUCH BAROCLINIC
INFLUENCE THE DEEP TROUGH OVER THE EASTERN U.S. WILL HAVE ON
SANDY...AND ALSO WHAT THE VERTICAL STRUCTURE OF SANDY WILL BE AFTER
48 HOURS. ALL OF THE GLOBAL MODELS MAINTAIN SIGNIFICANT RAINFALL
AMOUNTS IN EXCESS OF 2 INCHES NEAR THE CENTER THROUGH 120 HOURS...
WHICH SUGGESTS THAT SANDY WILL MAINTAIN SOME CONVECTION AND
POSSIBLY AN INNER-CORE WARM STRUCTURE THAT WOULD KEEP SOME TROPICAL
CHARACTERISTICS ASSOCIATED WITH THE SYSTEM. THE NEW INTENSITY
FORECAST IS SIMILAR TO THE LGEM AND DECAY-SHIPS INTENSITY MODELS.
THE FORECAST WILL STILL CALL FOR SANDY TO BECOME POST-TROPICAL BY
120 HOURS...ALTHOUGH THIS REMAINS LOW CONFIDENCE.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  25/0900Z 20.9N  75.8W   90 KT 105 MPH
 12H  25/1800Z 23.1N  75.7W   85 KT 100 MPH
 24H  26/0600Z 25.4N  76.1W   80 KT  90 MPH
 36H  26/1800Z 26.8N  76.6W   75 KT  85 MPH
 48H  27/0600Z 28.1N  76.3W   70 KT  80 MPH
 72H  28/0600Z 31.2N  73.7W   65 KT  75 MPH
 96H  29/0600Z 34.5N  70.5W   65 KT  75 MPH
120H  30/0600Z 37.5N  70.5W   60 KT  70 MPH...POST-TROPICAL
 
$$
FORECASTER STEWART
 
NNNN


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Page last modified: Monday, 31-Dec-2012 12:09:55 UTC