041  
FXCA20 KWBC 101149  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
748 AM EDT TUE OCT 10 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM OCT 10/06  
UTC: SCATTERED DEEP CONVECTION IS OCCURRING OFF THE COASTS OF  
PUERTO RICO AND IN THE VIRGIN ISLANDS...AS THE REGION LIES UNDER  
THE INFLUENCE OF STRONG UPPER TROUGH TO THE NORTH...THAT IS  
INTERACTING WITH A CONVECTIVELY UNSTABLE AIR MASS AND WITH AN  
ILL-DEFINED TROPICAL WAVE APPROACHING FROM THE EAST. THE UPPER  
TROUGH CENTERS AT 24N 68W WHILE THE WAVE EXTENDS AN ILL-DEFINED  
AXIS AT 62-63W. WELL TO THE EAST OF THE UPPER TROUGH...A MID-UPPER  
RIDGE EXTENDS AN AXIS FROM THE NORTHERN ATLANTIC AT 15N 45W WEST  
INTO THE WINDWARD ISLANDS.  
 
ANOTHER WET DAY IS EXPECTED IN PUERTO RICO AND THE VI AS THE UPPER  
TROUGH INTERACTS WITH THE UNSTABLE AIR MASS AND THE APPROACHING  
TROPICAL WAVE. UNDER THE INFLUENCE OF THE UPPER TROUGH...MODELS  
CONTINUE SHOWING A STEERING FLOW FROM THE SOUTH PREVAILING THROUGH  
WEDNESDAY EVENING. ON TUESDAY...WIND SPEEDS WILL BE WEAK ENOUGH TO  
ALLOW THE DEVELOPMENT OF HEAVY-RAIN PRODUCING THUNDERSTORMS IN  
NORTHERN AND NORTHEASTERN PUERTO RICO. DURING WEDNESDAY...AN  
INCREASE IN THE WIND SPEEDS WILL PROVIDE TOO MUCH SHEAR TO SUSTAIN  
HEAVY RAIN PRODUCING THUNDERSTORMS...THUS THE DECREASING TREND IN  
RAINFALL ACCUMULATIONS AFTER TUESDAY IS TO CONTINUE. AFTER THIS  
PERIOD...MODELS CONTINUE SHOWING THE MID-LEVEL RIDGE ESTABLISHING  
OVER THE REGION FROM THE EAST. THIS WILL STRENGTHEN THE SUBSIDENCE  
CAP AND LEAD TO A DRYING IN THE MID-LEVELS...WHICH WILL SUSTAIN A  
FURTHER DECREASE IN RAINFALL ACCUMULATIONS...AND A TRANSITION INTO  
A PATTERN DOMINATED MOSTLY BY TRADE WIND SHOWERS AFTER WEDNESDAY  
EVENING.  
 
IN TERMS OF ACCUMULATIONS...EXPECTING MAXIMA OF NEAR 2 INCHES ON  
TUESDAY AFTERNOON ALONG MOST OF NORTHERN PUERTO RICO...INCLUDING  
THE SAN JUAN METRO AREA. ISOLATED MAXIMA OF 2-3 INCHES IS EXPECTED  
IN NORTHEASTERN PUERTO RICO...WITH LARGEST ACCUMULATIONS OCCURRING  
DURING THE MID-AFTERNOON. FROM THE EARLY EVENING INTO WEDNESDAY  
MORNING...MOST WIDESPREAD SHOWERS WILL ORGANIZE OVER THE VIRGIN  
ISLANDS INTO SOUTHERN PUERTO RICO TO PRODUCE MAXIMA OF NEAR 1  
INCH. ISOLATED LARGER AMOUNTS ARE EXPECTED IN THUNDERSTORMS.  
DURING WEDNESDAY...THE ENHANCED WIND SHEAR AND FAST ~15KT  
SOUTHERLY FLOW AT 850 AND 700 HPA WILL LEAD TO SCATTERED RAINFALL  
AMOUNTS ACROSS THE ISLANDS...WITH MAXIMA OF 0.75 INCHES IN  
NORTHERN PUERTO RICO. ACCUMULATIONS ARE TO DECREASE AFTER THIS  
PERIOD.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
GALVEZ...WPC (USA)  

 
 
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