409  
FXCA20 KWBC 261257  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
856 AM EDT THU SEP 26 2024  
 
WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI SEP 26/12UTC:  
 
OVER THE NEXT SEVERAL DAYS...THE MAIN RAINFALL PATTERN OVER  
PR/USVI WILL BE RELATIVELY NORMAL...WITH GENERALLY SCATTERED  
SHOWERS ACROSS EASTERN PR AND THE USVI...WITH AFTERNOON CONVECTION  
ACROSS PORTIONS OF WESTERN PR. HOWEVER...THE AMOUNTS OF RAIN WILL  
VARY AFTER CONSIDERING SEVERAL FACTORS. OUT OF THE NEXT 5  
DAYS...FRIDAY IS EXPECTED TO BE THE WETTEST DAY AS A TROPICAL WAVE  
PASSES THROUGH THE AREA...WHILE AT THIS TIME TUESDAY IS FORECAST  
TO BE THE DRIEST DAY...THOUGH NOT COMPLETELY WITHOUT RAINFALL. THE  
TOTAL RAINFALL ACCUMULATION OVER 5 DAYS IS FORECAST TO BE NEAR 4  
INCHES ACROSS WESTERN PR AND NEAR 2 INCHES ACROSS EASTERN TO  
CENTRAL PR...AS WELL AS ACROSS THE USVI.  
 
THE AVAILABLE MOISTURE WILL GRADUALLY INCREASE TODAY ACROSS THE  
NORTHEAST CARIBBEAN AS A SFC TROUGH AND A TROPICAL WAVE MOVES  
ACROSS THE AREA. BASED ON THE LATEST GUIDANCE...THE PRECIPITABLE  
WATER VALUES WILL INCREASE TODAY FROM AROUND 1.96 INCHES IN THE  
26/12Z SOUNDING...TO AROUND 2.3 INCHES TONIGHT...HOVERING OVER 2  
INCHES INTO FRIDAY. THIS INCREASE IN MOISTURE WILL HELP IN THE  
DEVELOPMENT OF SHOWERS AND THUNDERSTORMS TODAY AND FRIDAY. A DRIER  
AIR MASS WILL MOVE IN AFTER FRIDAY...KEEPING PRECIPITABLE WATER  
VALUES IN THE NORMAL RANGE THIS WEEKEND THROUGH NEXT WEEK. THE  
OVERALL MOISTURE WILL ALSO INCREASE UP INTO THE MID LEVELS...WITH  
RELATIVE HUMIDITY INCREASING TO ABOVE NORMAL LEVELS THROUGH  
FRIDAY...THEN REMAINING IN THE NORMAL RANGE FROM SATURDAY ONWARD.  
ALTHOUGH SOME THUNDERSTORMS COULD BE STRONG AT TIMES TODAY AND  
FRIDAY...THE MID LEVELS WILL GRADUALLY GET WARMER TODAY  
ONWARD...AND EVEN THOUGH THE EGDI ALGORITHM DOES SUGGEST  
THUNDERSTORMS OVER THE NEXT COUPLE OF DAYS...THE GR02T ALGORITHM  
DOES NOT SUGGEST A PARTICULARLY HIGH CHANCE OF SEVERE  
THUNDERSTORMS.  
 
FROM SATURDAY ONWARD...WITH THE ARRIVAL OF THE DRIER AIR  
MASS...PERSISTENT EASTERLY TO ENE TRADES WILL PERSIST INTO NEXT  
WEEK...AS A SFC HIGH MOVES INTO THE CENTRAL ATLANTIC. THE MID  
LEVELS FROM THE WEEKEND ONWARD WILL HAVE EITHER A ZONAL EASTERLY  
WIND FLOW OR A WEAK RIDGE OVER THE NORTHEAST CARIBBEAN. THE UPPER  
LEVELS WILL BE HAVE A HIGH PRESSURE OVER THE WESTERN TROPICAL  
ATLANTIC AND A LOW PRESSURE OVER THE EASTERN CARIBBEAN. THIS WILL  
CAUSE STRONGER WINDS ALOFT...BUT PEAKING NEAR 55 KT BY SUNDAY  
AFTERNOON. OTHER THAN THE RELATIVELY STRONGER WINDS ALOFT ON  
SUNDAY...THE UPPER LEVELS WILL HAVE EASTERLY WINDS AT UNDER 40 KT.  
THIS MID TO UPPER LEVEL PATTERN...WITH NEAR NORMAL MOISTURE...WILL  
CAUSE THE PRECIPITATION OVER PR/USVI TO BE STRONGLY INFLUENCED BY  
THE LOCAL EFFECTS. FOR THAT REASON THE MAIN RAINFALL PATTERN IS  
FORECAST TO BE THAT OF SCATTERED SHOWERS ACROSS EASTERN PR AND THE  
USVI...WITH LOCALLY INDUCED AFTERNOON CONVECTION ACROSS PORTIONS  
OF WESTERN PR.  
 
ALAMO...WPC (USA)  
 
 
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