540
FXCA20 KWBC 161446
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
946 AM EST THU JAN 16 2025
WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI JAN 16 14 UTC:
THE LATEST CFS MJO FORECAST IS SUGGESTING AN UPPER DIVERGENT MJO
FOR THE NEXT FEW DAYS...BUT TRANSITIONING TO UPPER CONVERGENT BY
NEXT WEEK ONWARD. THAT BEING SAID...THE LATEST OBSERVATIONS ARE
SUGGESTING A WEAKER UPPER DIVERGENT PATTERN THAT WHAT THE MODEL IS
SUGGESTING...SO THERE MAY BE A BIAS TOWARDS DIVERGENCE ALOFT BY
THE MODEL COMPARED TO WHAT IT IS ACTUALLY BEING OBSERVED.
OVER THE NEXT SEVERAL DAYS...RELATIVELY BENIGN WEATHER IS EXPECTED
ACROSS PR/USVI...WITH MAINLY BRIEF SHOWERS OVER NORTH AND EAST PR
AS WELL AS THE USVI. HOWEVER...OUT OF THE NEXT 7 DAYS...SATURDAY
MAY BE THE DAY WITH MOST RAINFALL OVER PR/USVI...WITH THE GLOBAL
MODELS SUGGESTING AS MUCH AS AN INCH OF RAIN ACROSS PORTIONS OF
NORTHEASTERN PR WITH ISOLATED HIGHER AMOUNTS. THERE IS ALSO A COLD
FRONT MOVING SOUTH ACROSS THE TROPICAL ATLANTIC...BUT THIS IS
EXPECTED TO BECOME STATIONARY AND STALL NORTH OF PR...NEAR 20N BY
FRIDAY.
IN TERMS OF OVERALL MOISTURE...NEAR NORMAL PRECIPITABLE WATER IS
EXPECTED OVER THE ISLANDS OVER THE NEXT COUPLE OF DAYS...BUT AN
INCREASE TO ABOVE NORMAL MOISTURE IS FORECAST FOR SATURDAY AS A
SHEAR-LINE APPROACHES THE LOCAL ISLANDS. BY SUNDAY ONWARD...THE
AVAILABLE MOISTURE WILL DECREASE ONCE AGAIN TO NEAR NORMAL LEVELS.
THE LOW LEVEL WINDS WILL BE MAINLY FROM THE NNE TO NE LATE THIS
WEEK INTO SATURDAY...BUT AS THE SHEAR LINE APPROACHES THE
ISLANDS...THE WINDS WILL START BECOMING NE TO ENE WITH STRONGER
WIND SPEEDS...THEN EASTERLY WINDS ARE FORECAST FROM SUNDAY ONWARD.
IN THE MID AND UPPER LEVELS...THE LOCAL ISLANDS ARE UNDER THE
INFLUENCE OF AN UPPER RIDGE TODAY AND WILL BE THROUGH THE DAY ON
FRIDAY. BY LATE FRIDAY INTO SATURDAY...AND UPPER TROUGH WILL START
APPROACHING FROM THE WEST AND ITS AXIS IS EXPECTED TO MOVE THROUGH
ON SATURDAY. THIS MID AND UPPER LEVEL TROUGH PASSAGE COINCIDES
WITH THE INCREASE IN MOISTURE AND SHEAR-LINE OVER THE LOCAL
ISLANDS. THEREFORE THE CHANCES OF RAIN WILL INCREASE SIGNIFICANTLY
ON SATURDAY. THEREAFTER...THE MOISTURE WILL DECREASE TO NEAR
NORMAL...THEN MID AND UPPER LEVEL SUBSIDENCE IS EXPECTED TO
DOMINATE OVER THE LOCAL AREA.
AT THE SURFACE...THERE IS A HIGH PRESSURE EXTENDING INTO THE
WESTERN TROPICAL ATLANTIC WHILE A SFC LOW MOVES EAST TO THE NORTH
OF BERMUDA. THAT SAID...THE SFC HIGH PRESSURE WILL PREVAIL OVER OF
JUST NORTH OF PR FOR THE NEXT SEVERAL DAYS. THE HIGH PRESSURE
SYSTEM IS EXPECTED TO CENTER ITSELF OVER THE CENTRAL ATLANTIC BY
MONDAY. THIS SURFACE HIGH PRESSURE MIGRATION AND THE
AFOREMENTIONED SHEAR-LINE APPROACHING WILL INFLUENCE THE WIND
DIRECTION OVER THE LOCAL AREA.
THE WIND DIRECTION WILL HAVE A SIGNIFICANT IMPACT ON THE LOCATION
OF THE RAINFALL. GIVEN THAT THE MID AND UPPER LEVELS WILL BE
MAINLY UNDER THE INFLUENCE OF A HIGH PRESSURE RIDGE...EXCEPT FOR
SATURDAY...MOST OF THE SHOWER ACTIVITY IS EXPECTED TO BE
RELATIVELY SHALLOW. THE EGDI ALGORITHM IS ALSO SUGGESTING THAT
THERE IS NO REAL RISK OF THUNDERSTORM DEVELOPMENT OVER
PR/USVI...WITH THE EXCEPTION OF LATE FRIDAY INTO SATURDAY AS THE
MID AND UPPER TROUGH APPROACHED FROM THE WEST AND MOISTURE
INCREASES. AT THAT POINT...THE EGDI ALGORITHM DOES SHOW A CHANCE
FOR VERY ISOLATED THUNDERSTORMS. ONCE AGAIN...MOST OF THE RAIN IS
EXPECTED TO AFFECT MAINLY NORTH AND EASTERN PR AS WELL AS THE
USVI...PARTICULARLY ST THOMAS AND ST JOHN. WESTERN PR IS EXPECTED
TO OBSERVE MAINLY FAIR WEATHER...WITH A CHANCE OF RAIN ON SATURDAY
DUE TO THE INCREASE IN MOISTURE AND THE UPPER TROUGH APPROACHING.
ALAMO...WPC(USA)
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