997  
WTNT43 KNHC 282052  
TCDAT3  
 
TROPICAL STORM PHILIPPE DISCUSSION NUMBER 5  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182017  
500 PM EDT SAT OCT 28 2017  
 
SATELLITE IMAGES, RADAR DATA FROM CUBA AND KEY WEST, AND SURFACE  
OBSERVATIONS INDICATE THE DEPRESSION HAS TURNED NORTHWARD OVER THE  
PAST FEW HOURS, AND HAS ALSO STRENGTHENED INTO A TROPICAL STORM.  
THE INITIAL INTENSITY OF 35 KT IS BASED ON A SURFACE OBSERVATION OF  
35 KT IN A BRIEF SQUALL FROM GRAND CAYMAN AT 1444Z, A RECENT AMSU  
ESTIMATE OF 37 KT, AND AVERAGE KEY WEST DOPPLER RADAR VELOCITIES OF  
40 KT BETWEEN 10,000-12,000 FT JUST NORTH OF THE CUBAN COAST; THE  
LATTER DATA EQUATES TO AN APPROXIMATE SURFACE WIND SPEED OF 36 KT.  
 
THE INITIAL MOTION ESTIMATE IS NOW 355/25 KT BASED ON RADAR DATA AND  
HIGH-RESOLUTION GOES-16 VISIBLE SATELLITE IMAGERY OVER THE PAST 2-3  
HOURS. THE LOW-LEVEL WIND FLOW PATTERN FOR THE NEXT 6 HOURS OR SO IS  
FORECAST TO BE COMPLEX, WITH A NEW NON-TROPICAL SURFACE LOW HAVING  
RECENTLY FORMED ABOUT 100 NMI WEST OF KEY WEST, FLORIDA. THIS  
FEATURE APPEARS TO HAVE DEVELOPED BENEATH AN UPPER-LEVEL JET  
ENTRANCE REGION AHEAD OF AN APPROACHING COLD FRONT. THE GLOBAL,  
REGIONAL, AND EVEN THE CONVECTIVE-SCALE MODELS ARE NOW SHOWING THE  
CENTER OF PHILIPPE MOVING GENERAL NORTHWARD ACROSS THE STRAITS OF  
FLORIDA THIS EVENING AND MERGING WITH THE NON-TROPICAL LOW AROUND  
0000Z. AFTER THE MERGER OVER FLORIDA BAY, THE VARIOUS MODELS ARE IN  
GOOD AGREEMENT ON PHILIPPE MOVING NORTHEASTWARD TO  
EAST-NORTHEASTWARD ACROSS EXTREME SOUTHERN FLORIDA OR THE FLORIDA  
KEYS OVERNIGHT AS THE CYCLONE IS ACCELERATED AHEAD OF THE  
AFOREMENTIONED FRONTAL SYSTEM AND STRONG MID-/UPPER-LEVEL TROUGH.  
AFTER REACHING THE NORTHWESTERN BAHAMAS BY 1200Z SUNDAY MORNING,  
PHILIPPE IS FORECAST TO ACCELERATE FURTHER TOWARDS THE NORTHEAST AT  
FORWARD SPEEDS OF 30-35 KT, BY SUNDAY AFTERNOON AND EVENING,  
REMAINING WELL OFFSHORE OF THE CAROLINAS. BY 36 HOURS, PHILIPPE IS  
EXPECTED TO PASS ABOUT MIDWAY BETWEEN BERMUDA AND THE SOUTHEASTERN  
UNITED STATES, AND GRADUALLY GETTING PULLED NORTH-NORTHEASTWARD UP  
THE EAST SIDE OF A POWERFUL BAROCLINIC LOW THAT IS FORECAST TO  
DEVELOP NEAR CAPE HATTERAS AND MOVE NORTHWARD NEAR THE U.S. EAST  
COAST. THE NHC TRACK GUIDANCE IS IN REASONABLE AGREEMENT ON THIS  
DEVELOPING TRACK SCENARIO, AND LIES BETWEEN THE GFS MODEL, WHICH  
TAKES PHILIPPE ACROSS THE FLORIDA KEYS, AND THE ECMWF MODEL, WHICH  
MOVES THE CYCLONE FARTHER NORTH OVER SOUTH FLORIDA.  
 
THE VERTICAL WIND SHEAR AFFECTING PHILIPPE IS EXPECTED TO REMAIN  
FAVORABLE FOR STRENGTHENING TO OCCUR FOR THE NEXT 24 HOURS, ALONG  
WITH AN ADDITIONAL BAROCLINIC BOOST FROM THE AFOREMENTIONED  
UPPER-LEVEL JET MAXIMUM. BY 36 HOURS, STRONG BAROCLINIC FORCING  
ASSOCIATED WITH THE APPROACHING FRONTAL SYSTEM ARE FORECAST TO  
INDUCE ADDITIONAL STRENGTHENING BEFORE THE CYCLONE MERGES WITH  
THE FRONTAL SYSTEM AND BECOMES AN EXTRATROPICAL LOW BY 48 HOURS.  
DISSIPATION OR ABSORPTION BY A LARGER EXTRATROPICAL LOW IS EXPECTED  
BY 72 HOURS WHEN THE SYSTEM IS LOCATED OVER THE COLD WATERS OF THE  
NORTH ATLANTIC.  
 
KEY MESSAGES:  
 
1. ALTHOUGH THE CENTER OF PHILIPPE IS NOW FORECAST TO MOVE ACROSS  
THE FLORIDA KEYS OR EXTREME SOUTH FLORIDA, MOST OF THE STRONGEST  
WINDS ARE EXPECTED TO REMAIN EAST AND SOUTHEAST OF THE CENTER.  
HOWEVER, TROPICAL-STORM-FORCE WINDS, MAINLY IN GUSTS, COULD OCCUR  
IN BRIEF HEAVY SQUALLS ACROSS THE UPPER FLORIDA KEYS AND SOUTHEAST  
FLORIDA OVERNIGHT. FOR THAT REASON, A TROPICAL STORM WATCH REMAINS  
IN EFFECT FOR THESE AREAS.  
 
2. REGARDLESS OF THE EXACT TRACK OF PHILIPPE, THE PRIMARY THREAT  
FROM THIS SYSTEM WILL BE HEAVY RAINFALL THAT CAN CAUSE LOCALIZED  
FLOODING ACROSS PORTIONS OF CUBA, THE FLORIDA KEYS, AND SOUTH  
FLORIDA.  
 
FORECAST POSITIONS AND MAX WINDS  
 
INIT 28/2100Z 23.0N 82.6W 35 KT 40 MPH  
12H 29/0600Z 26.0N 80.1W 45 KT 50 MPH  
24H 29/1800Z 31.5N 75.3W 50 KT 60 MPH  
36H 30/0600Z 36.6N 70.5W 55 KT 65 MPH  
48H 30/1800Z 42.0N 66.0W 50 KT 60 MPH...POST-TROP/EXTRATROP  
72H 31/1800Z...DISSIPATED  
 

 
FORECASTER STEWART  
 
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