568  
WTNT43 KNHC 290241  
TCDAT3  
 
TROPICAL STORM PHILIPPE DISCUSSION NUMBER 6  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182017  
1100 PM EDT SAT OCT 28 2017  
 
PHILIPPE HAS A VERY NON-CLASSICAL STRUCTURE FOR A TROPICAL CYCLONE  
THIS EVENING. A COMBINATION OF SATELLITE IMAGERY, RADAR DATA, AND  
SURFACE OBSERVATIONS SHOW THAT THE CIRCULATION CENTER IS ELONGATED  
NORTHWEST-SOUTHEAST FROM SOUTHWEST OF NAPLES, FLORIDA, TO CENTRAL  
CUBA WITH AT LEAST THREE VORTICITY CENTERS PRESENT IN THIS AREA.  
THE ESTIMATED CENTER POSITION IS A MEAN OF THE MULTIPLE VORTICITY  
CENTERS, WITH THIS POSITION NEAR THE REGION OF LOWEST PRESSURE  
SUGGESTED BY THE SURFACE OBSERVATIONS. CURRENTLY, THE PRIMARY DEEP  
CONVECTION IS LOCATED FROM THE NORTHWESTERN BAHAMAS SOUTHWESTWARD  
ACROSS CUBA INTO THE CARIBBEAN, WITH A SMALLER AREA OF CONVECTION  
OVER THE SOUTHEASTERN GULF OF MEXICO. THE INITIAL INTENSITY  
REMAINS 35 KT, BASED MAINLY ON CONTINUITY FROM THE PREVIOUS  
ADVISORY.  
 
THE INITIAL MOTION IS A RATHER UNCERTAIN 015/21. A DEEP-LAYER  
TROUGH AND DEVELOPING SURFACE LOW OVER THE EASTERN UNITED STATES  
SHOULD CAUSE PHILIPPE TO TURN NORTHEASTWARD SOON, FOLLOWED BY A  
RAPID NORTHEASTWARD MOTION ACROSS THE SOUTHERN END OF THE FLORIDA  
PENINSULA INTO THE ATLANTIC. THE CYCLONE SHOULD CONTINUE TO MOVE  
AROUND THE LARGE BAROCLINIC SYSTEM UNTIL IT IS ABSORBED AFTER THE  
48 H POINT. THE NEW FORECAST TRACK IS A BLEND OF THE PREVIOUS  
FORECAST AND THE CURRENT GUIDANCE, AND IT IS SHIFTED TO THE NORTH  
OF THE PREVIOUS TRACK BASED MAINLY ON THE CURRENT INITIAL POSITION.  
 
IT IS UNCLEAR HOW MUCH ADDITIONAL STRENGTHENING PHILIPPE CAN DO AS  
A TROPICAL CYCLONE, AS THE SHEAR IS INCREASING OVER THE SYSTEM AND  
WATER VAPOR IMAGERY SHOWS DRY AIR ENTRAINMENT IN THE SOUTHWESTERN  
QUADRANT. HOWEVER, THE UPPER-LEVEL DIVERGENCE OVER THE SYSTEM IS  
VERY STRONG, AND THE LARGE-SCALE MODELS FORECAST DEEPENING AS THE  
CENTER CROSSES SOUTHERN FLORIDA AND THE BAHAMAS. IN ADDITION, THE  
INCREASING FORWARD SPEED MAY INCREASE THE MAXIMUM WINDS AS WELL.  
BASED ON THESE FACTORS, THE INTENSITY FORECAST CALLS FOR SOME  
INCREASE IN STRENGTH DURING THE NEXT 24-36 H. PHILIPPE IS LIKELY  
TO MERGE WITH A FRONTAL SYSTEM ASSOCIATED WITH THE EASTERN U. S.  
TROUGH IN ABOUT 36 H, AND THE MID-LATITUDE CYCLONE SHOULD  
COMPLETELY ABSORB PHILIPPE AFTER 48 H, IF NOT SOONER.  
 
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 WELL 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 29/0300Z 24.8N 82.1W 35 KT 40 MPH  
12H 29/1200Z 27.6N 78.9W 40 KT 45 MPH  
24H 30/0000Z 33.9N 74.0W 50 KT 60 MPH  
36H 30/1200Z 40.3N 69.6W 55 KT 65 MPH...POST-TROP/EXTRATROP  
48H 31/0000Z 48.0N 67.0W 50 KT 60 MPH...POST-TROP/EXTRATROP  
72H 01/0000Z...ABSORBED BY EXTRATROPICAL LOW  
 

 
FORECASTER BEVEN  
 
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