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Tropical Storm SANDY


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
 
TROPICAL STORM SANDY DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182012
1100 PM EDT MON OCT 22 2012
 
SINCE THE LAST RECON FLIGHT INTO SANDY AROUND 20Z...THE EARLIER
AMORPHOUS MASS OF CONVECTION EAST AND SOUTH OF THE CENTER HAS
BECOME MORE CONSOLIDATED NEAR THE CENTER...AND A CENTRAL DENSE
OVERCAST FEATURE APPEARS TO BE FORMING. IN ADDITION...INNER-CORE
CONVECTIVE BANDING HAS DEVELOPED SOUTH AND NORTH OF THE CENTER...
WITH OUTER BANDING FEATURES ALSO DEVELOPING OVER MUCH OF THE EASTERN
SEMICIRCLE. UPPER-LEVEL OUTFLOW HAS EXPANDED AND IMPROVED IN ALL
QUADRANTS...ESPECIALLY TO THE NORTHWEST WHERE IT HAD BEEN
RESTRICTED BY AN UPPER-LEVEL TROUGH. THE INITIAL INTENSITY OF 40 KT
IS BASED ON A BLEND OF EARLIER SFMR-ADJUSTED SURFACE WIND SPEEDS OF
42 KT AND 38 KT AROUND 20Z...AND THE RECENT INCREASE IN INNER-CORE
CONVECTIVE ORGANIZATION.

THE INITIAL MOTION ESTIMATE REMAINS STATIONARY. UPPER-AIR DATA AT
23/00Z INDICATED THAT MID-LEVEL HEIGHTS TO THE NORTH OF SANDY FROM
PUERTO RICO NORTHWESTWARD TO THE SOUTHEASTERN U.S. HAVE NOT CHANGED
OVER THE PAST 24 HOURS. THIS SUGGESTS...AT LEAST IN THE SHORT
TERM...THAT LITTLE POLEWARD MOTION IS LIKELY. BY 12-24 HOURS AND
CONTINUING THROUGH 72 HOURS...THE NHC MODEL GUIDANCE IS IN
EXCELLENT AGREEMENT ON A GENERAL SLOW NORTH TO NORTH-NORTHEASTWARD
MOTION TOWARD JAMAICA AND EASTERN CUBA AS A SHORTWAVE MOVES OFF THE
SOUTHEASTERN U.S. COAST AND WEAKENS THE SUBTROPICAL RIDGE THAT
CURRENTLY EXTENDS ACROSS FLORIDA AND THE BAHAMAS. BY DAYS 4 AND
5...HOWEVER...THE MODELS BEGIN TO DIVERGE SIGNIFICANTLY WITH THE
NORMALLY RELIABLE ECMWF TAKING SANDY NORTH-NORTHWESTWARD CLOSER TO
THE U.S. SOUTHEAST COAST...WHEREAS THE GFS...HWRF...GFDL...AND
OTHER LESS RELIABLE MODELS TAKE THE CYCLONE NORTH-NORTHEASTWARD.
GIVEN THE HISTORICAL RELIABILITY OF THE ECMWF MODEL...THE OFFICIAL
FORECAST TRACK REMAINS SIMILAR TO THE PREVIOUS ADVISORY TRACK...AND
LIES CLOSE TO A BLEND OF THE TVCA AND TV15 CONSENSUS MODELS...AND
THE FLORIDA STATE SUPERENSEMBLE MODEL.

REMAINING NEARLY STATIONARY OVER THE WARM WATERS OF SOUTHWESTERN
CARIBBEAN SEA IS NEVER A GOOD SIGN FOR THIS TIME OF THE YEAR.
THE GFS-BASED SHIPS MODEL IS INDICATING THAT SANDY SHOULD REMAIN IN
AN ENVIRONMENT OF VERTICAL SHEAR LESS THAN 5 KT...MID-LEVEL
MOISTURE GREATER THAN 80 PERCENT...OVER SSTS OF 29-30C...AND OVER
UPPER OCEAN HEAT CONTENT VALUES GREATER THAN 70 UNITS FOR AT LEAST
THE NEXT 24 HOURS. THESE ENVIRONMENTAL PARAMETERS ARE GENERALLY
CONDUCIVE FOR RAPID INTENSIFICATION TO OCCUR...AND THE SHIPS MODEL
REFLECTS THIS WITH A 64 PERCENT CHANCE OF A 30-KT INTENSITY
INCREASE DURING THE NEXT 24 HOURS. GIVEN THE RECENT IMPROVEMENT IN
THE INNER-CORE CONVECTIVE PATTERN...THE OFFICIAL INTENSITY FORECAST
HAS BEEN INCREASED OVER THE PREVIOUS ADVISORY AND NOW FORECASTS
SANDY TO BECOME A HURRICANE BY 36 HOURS BEFORE THE CYCLONE REACHES
JAMAICA. AFTER THAT...LAND INTERACTION WITH JAMAICA AND CUBA... 
COMBINED WITH INCREASING SOUTHWESTERLY VERTICAL SHEAR IS EXPECTED TO
INDUCE GRADUAL WEAKENING. BY 120 HOURS...SANDY IS EXPECTED TO
INTERACT WITH A DEEP UPPER-LEVEL TROUGH THAT COULD INDUCE
TRANSITION INTO A SIGNIFICANT SUBTROPICAL CYCLONE. THE OFFICIAL
INTENSITY FORECAST IS HIGHER THAN THE PREVIOUS ADVISORY THROUGH 48
HOURS...AND CLOSELY FOLLOWS A BLEND OF THE ICON...IV15...IVCN
INTENSITY CONSENSUS MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/0300Z 12.7N  78.6W   40 KT  45 MPH
 12H  23/1200Z 13.6N  78.4W   50 KT  60 MPH
 24H  24/0000Z 14.8N  77.9W   60 KT  70 MPH
 36H  24/1200Z 16.6N  77.5W   70 KT  80 MPH
 48H  25/0000Z 18.5N  77.1W   60 KT  70 MPH...INLAND OVER JAMAICA
 72H  26/0000Z 22.7N  75.8W   55 KT  65 MPH...OVER WATER
 96H  27/0000Z 25.7N  75.4W   55 KT  65 MPH
120H  28/0000Z 28.2N  73.6W   55 KT  65 MPH...SUBTROPICAL
 
$$
FORECASTER STEWART
 
NNNN


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