000
WTNT42 KNHC 122350
TCDAT2
 
TROPICAL STORM RAFAEL SPECIAL DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL172012
730 PM AST FRI OCT 12 2012
 
A COMBINATION OF SATELLITE AND AIR FORCE RESERVE HURRICANE HUNTER
AIRCRAFT DATA SHOWS THAT THE LOW PRESSURE SYSTEM IN THE EASTERN
CARIBBEAN SEA HAS FORMED A CLOSED CIRCULATION...ALBEIT ONE WITH A
LARGE AREA OF LIGHT AND VARIABLE WINDS NEAR THE CENTER.
THEREFORE...THE SYSTEM NOW MEETS THE CRITERIA TO BE CONSIDERED A
TROPICAL CYCLONE. THE AIRCRAFT REPORTED 1500-FT FLIGHT-LEVEL WINDS
OF 43 KT AND SMFR WINDS OF 35 KT NEAR ST. VINCENT...AND BASED ON
THESE DATA THE SYSTEM IS UPGRADED TO TROPICAL STORM RAFAEL.  MOST OF
THE DEEP CONVECTION IS DISPLACED WELL EAST AND SOUTHEAST OF THE
CENTER DUE TO ABOUT 20 KT OF SOUTHWESTERLY SHEAR ON THE EAST SIDE
OF AN UPPER-LEVEL LOW CENTERED SOUTHWEST OF PUERTO RICO. THE SHIPS
MODEL SHOWS THE SHEAR PERSISTING FOR THE NEXT DAY OR SO BEFORE
RELAXING A BIT AS THE UPPER-LOW SHEARS OUT AND LIFTS NORTHWARD.
ONLY SLOW STRENGTHENING IS EXPECTED DURING THE FORECAST PERIOD.
SUBSEQUENTLY...AS THE SHEAR FROM THE UPPER LOW DECREASES...THE
CYCLONE BECOMES EMBEDDED IN STRONG SOUTHWESTERLY FLOW AHEAD OF A
LONGWAVE TROUGH AMPLIFYING OFF THE U.S. EAST COAST. THE OFFICIAL
NHC FORECAST IS CLOSEST TO THE SHIPS MODEL GUIDANCE THROUGH THE
PERIOD.
 
GIVEN THE RECENT FORMATION OF THE CENTER...THE INITIAL MOTION
ESTIMATE IS A VERY UNCERTAIN 320/8. A GENERAL NORTH-NORTHWESTWARD
MOTION IS EXPECTED FOR THE FIRST COUPLE OF DAYS OF THE FORECAST
PERIOD AS THE CYCLONE MOVES INTO A WEAKNESS IN THE SUBTROPICAL
RIDGE. AT DAYS 3 THROUGH 5 AN ACCELERATION TOWARD THE NORTH AND
THEN TOWARD THE NORTH-NORTHEAST IS SHOWN AS A DEEP LAYER TROUGH
MOVES OFF THE U.S. EAST COAST. THERE IS A LARGE ALONG-TRACK SPREAD
IN THE GUIDANCE LATE IN THE PERIOD. THE GFS...GFS ENSEMBLE
MEAN...AND HWRF/GFDL MODELS SHOW THE CYCLONE ACCELERATING AHEAD OF
A CLOSED LOW SITUATED OVER THE NORTHEAST U.S. BY DAYS 4 AND 5. THE
ECMWF AND UKMET SHOW A MORE PROGRESSIVE UPPER-LEVEL PATTERN
SOLUTION THAT FAILS TO CAPTURE THE CYCLONE AS QUICKLY. THE NHC
TRACK IS A LITTLE SLOWER THAN THE TVCA MULTI-MODEL CONSENSUS
THROUGH THE PERIOD GIVEN THE UNCERTAINTY IN THE FORWARD SPEED...BUT
IS FASTER THAN A BLEND OF THE GFS AND ECMWF MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  12/2330Z 15.0N  63.1W   35 KT  40 MPH
 12H  13/0600Z 16.2N  63.6W   35 KT  40 MPH
 24H  13/1800Z 18.0N  64.0W   40 KT  45 MPH
 36H  14/0600Z 19.6N  64.4W   45 KT  50 MPH
 48H  14/1800Z 21.4N  65.6W   50 KT  60 MPH
 72H  15/1800Z 25.0N  67.5W   55 KT  65 MPH
 96H  16/1800Z 32.5N  65.0W   55 KT  65 MPH
120H  17/1800Z 43.0N  57.0W   50 KT  60 MPH
 
$$
FORECASTER BRENNAN/BEVEN