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FXCA20 KWBC 171414
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1013 AM EDT THU OCT 17 2024
WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI OCT 17/12UTC:
AS OF THIS WRITING...THE NATIONAL HURRICANE CENTER IS MONITORING
AN AREA OF LOW PRESSURE AND ASSOCIATED TROPICAL WAVE KNOWN AS
AL94...WHICH IS CURRENTLY LOCATED NEAR 56W. THIS SYSTEM HAS BEEN
GIVEN A 30 PERCENT CHANCE OF TROPICAL CYCLONE FORMATION THROUGH 7
DAYS. IN TERMS OF RAINFALL RELATED TO AL94...THE LATEST MODEL
GUIDANCE SUGGESTS THAT THE SYSTEM WILL MOVE TO THE WEST-NORTHWEST
OVER THE NEXT FEW DAYS...FURTHER SUGGESTING THAT THE HIGHEST
AMOUNTS OF RAIN WILL BE TO THE NORTH OF THE LOCAL ISLANDS LATE
FRIDAY INTO SATURDAY.
AS AL94 APPROACHES THE LOCAL ISLANDS...THE INCREASE IN MOISTURE
ASSOCIATED WITH IT WILL ALSO REMAIN TO THE NORTH OF PR/USVI...BUT
A BAND OF MOISTURE COULD MOVE THROUGH PR/USVI ON SATURDAY INTO
SUNDAY...CAUSING THE PRECIPITABLE WATER VALUES TO INCREASE TO
ABOVE NORMAL LEVELS...FOR THE WEEKEND AND LINGERING INTO EARLY
NEXT WEEK. THIS IS DUE TO A FRONTAL BOUNDARY AND PRE-FRONTAL
TROUGH THAT ARE EXPECTED TO BE ACROSS THE WESTERN TROPICAL
ATLANTIC LATE THIS WEEKEND INTO EARLY NEXT WEEK. THE MODEL
GUIDANCE SHOWS THIS FRONTAL BOUNDARY WEAKENING THROUGH NEXT
WEEK...BUT THE SURFACE TROUGH WILL REMAIN FAIRLY STATIONARY OVER
THE WESTERN TROPICAL ATLANTIC. THIS WILL CAUSE MOISTURE TO POOL
AHEAD OF THE TROUGH AND KEEP THE NORTHEAST CARIBBEAN WITH ABOVE
NORMAL MOISTURE THROUGH NEXT WEEK. HOWEVER...THE MODEL GUIDANCE
DOES SHOW A SMALL PATCH OF RELATIVELY DRIER AIR MOVING OVER
PR/USVI ON WEDNESDAY...BUT THE MOISTURE INCREASES RIGHT BACK FOR
THE LATTER PART OF THE FOLLOWING WORKWEEK. OVER THE NEXT FEW
DAYS...HOWEVER...THERE WILL BE PATCHES OF MOISTURE MOVING
IN...BRIEFLY INCREASING PRECIPITABLE WATER VALUES IN THE AFTERNOON
TODAY AND ON FRIDAY. COMBINED WITH THE EASTERLY WINDS AND LOCAL
EFFECTS...THE RAINFALL PATTERN TODAY AND FRIDAY WILL BE
TYPICAL...WITH PASSING SHOWERS AFFECTING THE USVI AND EASTERN
PR...THEN AFTERNOON CONVECTION DEVELOPING ACROSS WESTERN PR IN THE
AFTERNOON HOURS. THE INCREASE IN MOISTURE ON FRIDAY COULD BE A BIT
LONGER LASTING THAN TODAY...AND FRIDAY COULD HAVE A WIDER COVERAGE
OF RAINFALL THAN IS EXPECTED TODAY.
IN THE UPPER LEVELS THERE IS A BROAD HIGH PRESSURE OVER THE
CENTRAL TO WESTERN TROPICAL ATLANTIC...WHILE THERE IS AN INVERTED
TROUGH AXIS OVER THE CARIBBEAN...TO THE SOUTHWEST OF
PR/USVI...WHICH IS ASSOCIATED WITH AN UPPER LOW OVER NORTHERN
SOUTH AMERICA. BY FRIDAY INTO SATURDAY...THE UPPER HIGH PRESSURE
WILL MOVE WEST INTO THE WESTERN TROPICAL ATLANTIC...AND CENTER
NEAR THE BAHAMAS. PR/USVI WILL REMAIN IN THE PERIPHERY OF THE
UPPER HIGH PRESSURE THROUGH THE WEEKEND...BUT A BROAD UPPER TROUGH
WILL BE LOCATED TO THE NORTH OF PR EARLY NEXT WEEK...SLOWLY
DIGGING SOUTH WITH AXIS OVER HISPANIOLA...AND WILL START TO IMPACT
THE UPPER LEVEL WINDS OVER PR/USVI BY WEDNESDAY. IN THE MID
LEVELS...A TROUGH IS ASSOCIATED WITH AL94 WILL MOVE WEST
NORTHWEST...AND IS EXPECTED TO BE NORTH OF PR/USVI BY SATURDAY. AS
THE TROUGH CONTINUES TO MOVE WEST...THERE WILL BE A WEAK MID LEVEL
HIGH TO THE NORTHEAST OF THE NORTHEAST CARIBBEAN AND A BROAD MID
LEVEL TROUGH OVER THE WESTERN CENTRAL ATLANTIC...WITH AXIS DIGGING
INTO THE WESTERN TROPICAL ATLANTIC BY SUNDAY. THIS MID LEVEL
TROUGH WILL CONTINUE TO DIG SLOWLY TO THE SOUTH AND WILL HAVE ITS
AXIS ACROSS HISPANIOLA BY LATE TUESDAY INTO WEDNESDAY.
IN TERMS OF THE RAINFALL PATTERN...AS PREVIOUSLY MENTIONED...TODAY
AND FRIDAY ARE EXPECTED TO BE FAIRLY TYPICAL...BUT THE OVERALL
SYNOPTIC PATTERN WOULD FAVOR RAIN OVER EASTERN PR AND THE USVI
FROM SATURDAY ONWARD. BASED ON THE LATEST MODEL GUIDANCE...EASTERN
PR...INCLUDING VIEQUES AND CULEBRA MAY RECEIVE A 5-DAY RAINFALL
ACCUMULATION...THROUGH TUESDAY 22 OCT AT 12Z...OF AROUND 4-6
INCHES...WHILE CENTRAL TO WESTERN PR COULD OBSERVE AROUND 1-3
INCHES. THE USVI ARE FORECAST A 5-DAY ACCUMULATION OF AROUND 2-4
INCHES. ISOLATED HIGHER AMOUNTS ARE POSSIBLE WITH THE STRONGEST
THUNDERSTORMS...HOWEVER. ONE THING TO CONSIDER IS THAT THE
PROXIMITY TO THE FRONTAL BOUNDARY AND SFC TROUGH TO THE NORTHWEST
OF THE LOCAL ISLANDS INCREASES THE UNCERTAINTY IN THE RAINFALL
FORECAST...AND THE EGDI ALGORITHM SUGGESTS THE POTENTIAL OF
ISOLATED TO SCATTERED THUNDERSTORMS VERY CLOSE TO THE NORTHWEST OF
PR LATE THIS WEEKEND INTO EARLY NEXT WEEK.
ALAMO...WPC (USA)
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