801
FXCA20 KWBC 311400
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1000 AM EDT THU OCT 31 2024
WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI OCT 31/14UTC:
THE OVERALL WEATHER PATTERN CONTINUES TO BE RELATIVELY COMPLEX
OVER THE TROPICAL REGION. SHOWERS AND THUNDERSTORMS ARE ALREADY
AFFECTING MANY AREAS OF PR/USVI...PARTICULARLY ACROSS EASTERN PR
INTO THE USVI AND THE LOCAL CARIBBEAN WATERS. ACTIVE WEATHER IS
EXPECTED TODAY INTO FRIDAY...WITH AN IMPROVEMENT LATE FRIDAY INTO
EARLY IN THE WEEKEND. HOWEVER...UNCERTAINTY INCREASES
SIGNIFICANTLY FROM THIS WEEKEND ONWARD DUE TO MODEL DISAGREEMENT.
THE GLOBAL MODEL GUIDANCE IS IN SOME AGREEMENT IN THE SHORT
TERM...BUT THE GFS MODEL SEEMS TO BE INITIALIZING BETTER THAN THE
OTHER GLOBAL MODELS. THAT BEING SAID...FOR THIS WEEKEND
ONWARD...THE GFS MODEL HAS BEEN INCONSISTENT AND CHANGING FROM RUN
TO RUN WITH THE DEVELOPMENT OF AN AREA OF LOW PRESSURE IN THE
CARIBBEAN AND IN THE SOUTHWESTERN ATLANTIC...AS IT FAVORS THE
CONTINUED DEEPENING OF A LOW PRESSURE STEMMING FROM AN INDUCED
TROUGH JUST NORTH OF THE GREATER ANTILLES. THE ECMWF HAS BEEN A
BIT MORE CONSISTENT WITH ITS FORECAST FOR THIS WEEKEND AND IT HAS
BEEN GENERALLY MORE CONSERVATIVE WITH THE DEVELOPING OF THE LOW
PRESSURES IN THE TROPICAL REGION...WITH ITS LATEST RUN FAVORING A
BROAD CIRCULATION IN THE WESTERN CARIBBEAN MOVING INTO THE YUCATAN
PENINSULA. THIS LARGER SCALE PATTERN COULD HAVE AN IMPACT IN THE
LOCAL RAINFALL PATTERN OVER PR/USVI LATE THIS WEEKEND INTO NEXT
WEEK...AND THEREFORE THERE IS HIGHER THAN NORMAL UNCERTAINTY. AT
THIS TIME...THE 5-DAY FORECAST FOR PR/USVI FROM TODAY INTO MONDAY
MORNING...INDICATES RAINFALL AMOUNTS OF 4-6 INCHES ACROSS PORTIONS
OF NORTHERN AND EASTERN PR INTO VIEQUES AND CULEBRA...WHILE THE
USVI AND PORTIONS OF EAST-CENTRAL AND SOUTHERN PR COULD OBSERVE
2-4 INCHES. MOST OF THE WESTERN HALF OF PR IS FORECAST AROUND 1-2
INCHES. MOST OF THE RAINFALL IS EXPECTED TODAY AND FRIDAY...AND
SOME OF THE EXPECTED RAIN IS ALREADY OCCURRING.
AT THE SURFACE...THERE IS A HIGH PRESSURE IN THE WESTERN ATLANTIC
DOMINATING THE REGION. HOWEVER...THERE IS AN INDUCED TROUGH JUST
SSE OF PR/USVI...WHICH SATELLITE IMAGERY INDICATES HAS PLENTY OF
CONVECTION...AND THE TJUA RADAR IS ALSO MODERATE TO HEAVY SHOWER
ACTIVITY OVER THE AREA. ELSEWHERE IN THE REGION...THERE IS A
STATIONARY FRONT JUST EAST OF THE WINDWARD ISLANDS EXTENDING
NORTHEAST THROUGH THE TROPICAL ATLANTIC. THE MID LEVELS HAS A
POSITIVELY TILTED TROUGH WITH AXIS OVER HISPANIOLA THAT COULD
SLOWLY DEVELOP A LOW PRESSURE NORTH OF THE CARIBBEAN THIS WEEKEND
AS THE MID LEVEL TROUGH DEEPENS. HOWEVER THERE IS SOME MODEL
DISCREPANCY ON THE DEEPENING OF THIS TROUGH FROM THE WEEKEND
ONWARD. IN THE UPPER LEVELS...THERE IS ALSO A POSITIVELY TILTED
TROUGH OVER HISPANIOLA...BUT THE LATEST GUIDANCE IS SUGGESTING A
SHORTWAVE NEGATIVELY TILTED TROUGH WITH ITS AXIS JUST SOUTHWEST OF
PR TODAY...MOVING EAST AND HAVING ITS AXIS SOUTHEAST OF PR BY
FRIDAY MORNING. HAVING A NEGATIVELY TILTED SHORTWAVE TROUGH IN THE
PERIPHERY OF A POSITIVELY TILTED BROADER TROUGH COULD BE AN
INDICATION THAT THE TROUGH IS DEEPENING...ADDING TO THAT...THE
WINDS ON THE WEST SIDE OF THE BROAD TROUGH AXIS ARE
STRONGER...WHICH ALSO CAN BE INDICATIVE OF A DEEPENING TROUGH.
THAT BEING SAID...THE ACTUAL POSITIONING OF THE TROUGH AXIS AFTER
FRIDAY WOULD FAVOR CONVECTION FURTHER NORTH AND EAST OF THE LOCAL
ISLANDS...WITH BOTH THE GFS AND ECMWF INDICATING DECENT CONVECTION
WELL TO THE NORTH OF THE LOCAL ISLANDS FROM LATE FRIDAY INTO THIS
WEEKEND...MAINLY NEAR 20N ALONG A SHEAR-LINE THAT IS EXPECTED TO
DEVELOP OVER THE AREA.
ONCE AGAIN...GIVEN THE MODEL INCONSISTENCIES AND DIFFICULTY
SOLVING THE POTENTIAL FORMATION OF LOW PRESSURES IN THE CARIBBEAN
THIS WEEKEND...THE RAINFALL FORECAST FOR LATE THIS WEEKEND INTO
NEXT WEEK IS HIGHLY UNCERTAIN. BLENDING THE MODEL GUIDANCE FOR
EARLY NEXT WEEK...THE RAINFALL PATTERN FOR PR/USVI EARLY NEXT WEEK
COULD FAVOR HIGHER AMOUNTS OF RAIN OVER NORTH AND EASTERN PR INTO
THE USVI...WITH TOTALS BETWEEN 1-2 INCHES...WHILE WESTERN AND
SOUTHERN PR IS FORECAST TO OBSERVE LOWER AMOUNTS OF
RAIN...GENERALLY UNDER AN INCH EARLY NEXT WEEK.
ALAMO...WPC (USA)
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