689  
FXCA20 KWBC 151156  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
755 AM EDT SUN OCT 15 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE VI FROM OCT 15/06  
UTC: A TROPICAL WAVE IS CROSSING THE ISLANDS WHILE EXTENDING ITS  
AXIS ALONG EASTERN PUERTO RICO AT 65W. A SIGNIFICANT MOISTURE POOL  
LIES TO THE EAST OF THE AXIS. THIS POOL HAS PRECIPITABLE WATER  
VALUES EXCEEDING 60MM. ACCORDINGLY...NUMEROUS SHOWERS AND  
THUNDERSTORMS ARE OCCURRING OVER AND TO THE EAST OF THE VIRGIN  
ISLANDS. AT MID-UPPER LEVELS...A RIDGE CENTERS AT 16N 57W...WHILE  
A LOW CENTERS OVER THE CENTRAL BAHAMAS.  
 
AS THE TROPICAL WAVE MOVES ACROSS THE ISLANDS...EXPECTING A CHANGE  
IN WINDS TO SOUTH EASTERLIES EARLY ON SUNDAY. MODELS AGREE ON  
15-25KT SOUTHEASTERLY TRADES PERSISTING THROUGH THE NEXT 4 DAYS.  
ALSO...THEY CONTINUE SUGGESTING THAT THE ISLANDS WILL REMAIN UNDER  
THE INFLUENCE OF A MOIST PLUME THROUGH LATE WEDNESDAY. THREE  
FACTORS THAT ARE PLAYING AGAINST EXTREME RAINFALL ARE ENHANCED  
LOW-LEVEL SHEAR AND FAST MOVING CELLS...THE PREVALENCE OF A  
MID-UPPER LEVEL RIDGE PATTERN...AND THE UPPER CONVERGENT PHASE OF  
THE MADDEN-JULIAN OSCILLATION. YET...CONVECTIVE INSTABILITY WILL  
REMAIN HIGH THROUGH THE CYCLE TO FAVOR SEVERAL ROUNDS OF MODERATE  
PRECIPITATION...ESPECIALLY IN THE VIRGIN ISLANDS.  
 
IN TERMS OF ACCUMULATIONS...EXPECTING LARGEST AMOUNTS IN THE  
VIRGIN ISLANDS ON SUNDAY AS WIDESPREAD HEAVY-RAIN PRODUCING  
THUNDERSTORMS CONTINUE DEVELOPING INTO THE LATE MORNING. THIS WILL  
SUSTAIN RAINFALL ACCUMULATIONS OF 2-3 INCHES MOSTLY DURING MORNING  
HOURS. IN PUERTO RICO...LARGEST ACCUMULATIONS ARE EXPECTED IN  
EASTERN PORTIONS OF THE ISLAND...WHERE MAXIMA WILL ALSO REACH 2-3  
INCHES. ALONG THE SOUTHERN CORDILLERA AND NORTHWESTERN PUERTO RICO  
EXPECTING MAXIMA NEAR 1-1.5 INCHES IN ASSOCIATION WITH THE  
TROPICAL WAVE. BY MONDAY...EXPECTING A SIGNIFICANT DECREASE IN  
ACCUMULATIONS IN THE VIRGIN ISLANDS...YET...NUMEROUS SHOWERS WILL  
LEAD TO AMOUNTS NEAR 0.5 INCHES/DAY. IN PUERTO RICO...LARGEST  
ACCUMULATIONS ARE EXPECTED ONCE AGAIN IN EASTERN PORTIONS OF THE  
ISLAND MOSTLY DURING THE DAY...WHERE EXPECTING MAXIMA NEAR 1-1.5  
INCHES. IN CENTRAL AND WESTERN PUERTO RICO EXPECTING MAXIMA OF 0.5  
INCHES. DURING TUESDAY...EXPECTING ONCE AGAIN LARGEST  
ACCUMULATIONS IN EASTERN PUERTO RICO...WHERE MAXIMA WILL REACH  
2-2.5 INCHES. A SECONDARY MAXIMA IS EXPECTED IN NORTHWESTERN  
PUERTO RICO...WHERE AFTERNOON THUNDERSTORMS WILL LEAD TO MAXIMA OF  
0.75-1 INCH. DURING WEDNESDAY...LARGEST ACCUMULATIONS ARE EXPECTED  
IN NORTHWESTERN PUERTO RICO AND EXTREME NORTHEASTERN PUERTO  
RICO...WITH DAILY MAXIMA NEAR 0.75-1 INCH. A SHARP DRYING TREND  
FOLLOWS...AS DRY AIR MASS ARRIVES FROM THE ATLANTIC AND A STRONG  
CAP STARTS DEVELOPING ON THURSDAY.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
GALVEZ...WPC (USA)  

 
 
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