791  
FXCA20 KWBC 221200  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
800 AM EDT SUN OCT 22 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE VI FROM OCT 22/06  
UTC: FAIR AND WINDY CONDITIONS ARE TO CONTINUE INTO MID-NEXT  
WEEKS. TRADE WIND SHOWERS ARE FORECAST TO BE LIGHT...ISOLATED AND  
VERY BRIEF...AS THEY WILL BE STREAMING FROM EAST TO WEST EMBEDDED  
IN 15-20KT TRADES.  
 
AT UPPER LEVELS...A DEEP UPPER TROUGH TO THE NORTHWEST OF THE  
ISLANDS NOW CENTERS ON A LOW AT 26N 64W. THE TROUGH IS DEVELOPING  
AN AXIS TO THE SOUTH INTO PUERTO RICO. ALTHOUGH THIS TROUGH IS  
MEANDERING TO THE SOUTH EAST...ITS EXERTING LIMITED EFFECTS IN THE  
ISLANDS WHILE A DRY AIR MASS LINGERS IN THE MID-TROPOSPHERE. AT  
LOW LEVELS...A THE AXIS OF A TRADE WIND SURGE EXTENDS NOW TO THE  
WEST OF JAMAICA. BEHIND THE SURGE...OVER PUERTO RICO AND THE  
VI...A SUBSIDENCE CAP SITS AT 900 HPA AND VERY DRY AIR LIES OVER  
THE INVERSION. TRADE ARE ALSO FAST...AS WIND SPEEDS RANGE BETWEEN  
15 AND 20KT. THIS IS LEADING TO STREAMING LIGHT AND ISOLATED TRADE  
WIND SHOWERS.  
 
MODELS INDICATE THAT THE BASE OF THE UPPER TROUGH WILL MEANDER  
FROM PUERTO RICO IN SUNDAY MORNING TO THE LEEWARD  
ISLANDS-NORTHEASTERN VENEZUELA BY MONDAY EVENING. THIS WILL PLACE  
PUERTO RICO AND THE VI UNDER THE UPPER CONVERGENT PATTERN OF THE  
TROUGH...WHICH WILL CONTINUE SUSTAINING THE TRADE WIND CAP AND  
LIMITING THUNDERSTORM DEVELOPMENT. POSITIVE INTERACTION BETWEEN  
THE TROUGH AND THE MOISTURE PLUME IN THE SOUTHEASTERN CARIBBEAN IS  
FORECAST TO LIMIT TO LATITUDES TO THE SOUTH OF 15N...AND TO  
LONGITUDES TO THE EAST OF 65W. THIS WILL SUSTAIN A WET SPELL IN  
THE FRENCH ISLES AND WINDWARD ISLANDS DURING  
MONDAY-WEDNESDAY...WHILE PUERTO RICO AND THE VI CONTINUE  
EXPERIENCING FAIR CONDITIONS. UNDER THE INFLUENCE OF THE UPPER LOW  
TO THE NORTH...WINDS ARE TO DECREASE IN SPEED TO 10-15KT DURING  
TUESDAY...AND BY LATE TUESDAY/EARLY WEDNESDAY THEY WILL SHIFT TO  
SOUTHEASTERLIES. THIS WILL SHIFT THE AREAS OF AFTERNOON  
PRECIPITATION TO NORTHEASTERN PUERTO RICO BY MID-WEEK.  
 
IN THE MEAN TIME...ACTIVITY WILL BE CHARACTERIZED BY LIGHT...BRIEF  
AND ISOLATED TRADE WIND SHOWERS MOSTLY AFFECTING THE VIRGIN  
ISLANDS AND EASTERN PUERTO RICO. EXPECTING DAILY ACCUMULATIONS OF  
0.2 INCHES...AND MAXIMA OF 0.5 INCHES IN AREAS OF OROGRAPHIC  
UPLIFT. ALSO...AFTERNOON CONVECTION WILL CLUSTER IN EXTREME  
WESTERN PUERTO RICO. UNDER THE PROXIMITY OF THE UPPER  
TROUGH...EXPECTING ISOLATED THUNDERSTORMS TO DEVELOP. YET...THE  
SHEAR WILL BE TOO LARGE...AND THE MID-LEVELS TOO DRY TO SUSTAIN  
LONG LIVED HEAVY RAIN PRODUCING CELLS. THUS WE EXPECT ISOLATED  
MAXIMA NEARING 1 INCH IN THE STRONGEST THUNDERSTORMS BETWEEN  
MAYAGUEZ AND AGUADILLA ON A DAILY BASIS. AFTER TUESDAY...AFTERNOON  
CONVECTION WILL CONCENTRATE IN THE VICINITY OF AGUADILLA AND OTHER  
LOCATIONS IN NORTHWESTERN PUERTO RICO TO PRODUCE MAXIMA UNDER 1  
INCH.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
GALVEZ...WPC (USA)  

 
 
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