326
FXCA20 KWBC 291504
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1103 AM EDT TUE OCT 29 2024
SPECIAL DISCUSSION FOR PUERTO RICO AND THE USVI OCT 29/15UTC:
A RELATIVELY COMPLEX WEATHER PATTERN IS IN STORE FOR THE NORTHEAST
CARIBBEAN THROUGH THE REST OF THE WEEK. THERE ARE SEVERAL WEATHER
FEATURES TO CONSIDER...AS WELL AS DIFFERENT MODEL
SOLUTIONS...WHICH ADDS UNCERTAINTY TO THE FORECAST...PARTICULARLY
FOR THE LATTER PART OF THE WORKWEEK INTO THE WEEKEND. THAT BEING
SAID...ALL THINGS CONSIDERED...PUERTO RICO AND THE USVI MAY HAVE
SEVERAL DAYS WITH PLENTY OF CLOUDINESS FROM WEDNESDAY ONWARD...AND
THERE IS A RISK OF STRONG THUNDERSTORMS WITH HEAVY RAIN LATE
THURSDAY INTO FRIDAY...PARTICULARLY FOR EASTERN PR AND THE
NORTHERN USVI. THE GFS MODEL IS THE MOST AGGRESSIVE WITH THE
HIGHEST RAINFALL AMOUNTS OUT OF THE GLOBAL MODELS...BUT THE AI
VERSION OF THE ECMWF IS NOT FAR FROM THE GFS. IN ADDITION...THE
GFS MODEL SEEMS TO BE INITIALIZING BETTER AND IT CURRENTLY HAS A
BETTER HANDLE ON THE LARGER SCALE FEATURES AND OTHER SMALLER SCALE
FEATURES ACROSS THE TROPICAL REGION. THEREFORE...WE HAVE GIVEN THE
LATEST GFS AND THE GFS ENSEMBLES A POSITIVE NUDGE IN OUR FORECAST.
SYNOPTIC PATTERN...
CURRENTLY THERE IS A SFC LOW PRESSURE ACROSS THE CENTRAL TROPICAL
ATLANTIC...WITH A STATIONARY FRONT EXTENDING SOUTHWEST INTO AROUND
20N...AND EXTENDING ALONG 20N FROM NORTHEAST OF THE
LEEWARDS...WEST INTO WESTERN CUBA. THE PORTION OF THE STATIONARY
FRONT TO THE NORTH OF PR/USVI IS EXPECTED TO FRAGMENT
TODAY...WHILE THE EASTERN PORTION OF THE FRONT ADVANCES
SOUTHEASTERLY AS A COLD FRONT JUST TO THE EAST OF THE LEEWARD
ISLANDS...BECOMING STATIONARY TO THE EAST OF THE LESSER ANTILLES
BY THURSDAY NIGHT. MEANWHILE...A COL WILL DEVELOP OVER THE CENTRAL
TROPICAL ATLANTIC...AND A CONFLUENT WIND PATTERN WILL DEVELOP TO
THE WEST OF THE COL...CAUSING A SHEARLINE TO DEVELOP JUST NORTH OF
PR/USVI LATE IN THE WORKWEEK. BY THURSDAY AFTERNOON...ALTHOUGH
THERE IS SOME CHANGE IN TEMPERATURE NORTH OF THE SHEARLINE...THE
GRADIENT IS WEAK AND SOMEWHAT UNCLEAR NEAR 20N...THOUGH A BETTER
TEMPERATURE GRADIENT IS OBSERVED NEAR 25N...WHICH IS WELL NORTH OF
WHERE WE ARE ANALYZING THE SHEARLINE. ADDING TO THAT...THE SFC
WIND SPEED TO THE NORTH OF THE CARIBBEAN ISLANDS IS FORECAST TO BE
NEAR OR ABOVE 22 KNOTS...WHILE THE WINDS TO THE SOUTH OF THE
ISLANDS ARE FORECAST TO BE NEAR 12 KNOTS OR LESS. THIS SHEARLINE
IS FORECAST TO BECOME MORE PRONOUNCED LATE FRIDAY ONWARD...AS
WINDS MAY BE NEAR 25 KNOTS NEAR OF JUST NORTH OF 20N. THIS FEATURE
WILL ENHANCE LOW LEVEL VORTICITY OVER PR/USVI ON THURSDAY INTO
FRIDAY...THEN THE ENHANCED LOW LEVEL VORTICITY WILL MOVE NORTH
LATE FRIDAY INTO SATURDAY.
A POSITIVELY TILTED MID LEVEL TROUGH WILL HAVE ITS AXIS INTO
HISPANIOLA ON WEDNESDAY AFTERNOON. THIS TROUGH WILL SLOWLY MOVE
EAST AND ITS AXIS WILL BE NEAR PR/USVI ON THURSDAY INTO FRIDAY AS
IT WEAKENS. A WEAK MID LEVEL HIGH PRESSURE IS EXPECTED TO DEVELOP
OVER THE CARIBBEAN...EXTENDING INTO PR/USVI BY LATE FRIDAY INTO
THE WEEKEND. IN THE UPPER LEVELS...THERE IS ANOTHER POSITIVELY
TILTED TROUGH EXPECTED ON THURSDAY...BUT IT HAS ITS AXIS A BIT
FURTHER WEST THAN THE MID LEVEL TROUGH. THE UPPER TROUGH IS ALSO
EXPECTED TO MOVE EAST SLOWLY...AND AN UPPER LOW COULD DEVELOP
NORTH OF HISPANIOLA BY LATE THURSDAY INTO FRIDAY. DURING THIS
TIME...A WEAK UPPER JET DEVELOPS TO THE NORTH OF THE ISLANDS...AS
ANOTHER UPPER JET DEVELOPS AT THE BASE OF THE TROUGH JUST SOUTH OF
HISPANIOLA. STREAMLINE ANALYSIS INDICATES THAT ON THURSDAY INTO
FRIDAY...THERE COULD BE AN UPPER DIFFLUENT PATTERN OVER THE
NORTHEAST CARIBBEAN WHILE A...NEGATIVELY TILTED...UPPER SHORTWAVE
TROUGH MOVES SOUTH OF EASTERN HISPANIOLA...ALONG 70W...BY FRIDAY
MORNING. THIS PATTERN COULD FAVOR ACTIVE WEATHER ACROSS EASTERN PR
AND INTO THE USVI FROM LATE THURSDAY INTO FRIDAY...INCLUDING AREAS
AROUND VIEQUES AND CULEBRA...AS HEAT RELEASE FROM THE WARM WATERS
COMBINED WITH THE MID AND UPPER LEVEL INSTABILITY COULD CAUSE
STRONG NIGHTTIME CONVECTION. ALTHOUGH STRONG THUNDERSTORMS ARE
POSSIBLE...THE MID LEVEL TEMPERATURES ARE NOT FORECAST TO BE COLD
ENOUGH TO ENHANCE THE CHANCES FOR HAIL. AT THIS TIME...THE
EXPECTED PATTERN WOULD FAVOR STRONG THUNDERSTORMS WITH HEAVY RAIN
ON THURSDAY AFTERNOON AND OVERNIGHT INTO FRIDAY.
EVEN THOUGH THE AVAILABLE MOISTURE WILL BE ABOVE NORMAL FOR THE
NEXT 5 DAYS...WITH PRECIPITABLE WATER OVER 2 INCHES FOR MOST OF
THE TIME...THE EXPECTED SYNOPTIC SCALE PATTERN DOES NOT
PARTICULARLY FAVOR STRONG STRONG THUNDERSTORMS ACROSS CENTRAL TO
WESTERN PR. THE TYPICAL PATTERN WITH DIURNAL CONVECTION ACROSS
WESTERN PR IS POSSIBLE TODAY AND ON WEDNESDAY...BUT FROM THURSDAY
INTO FRIDAY THE RAINFALL PATTERN IS SHIFTED TO FAVOR EASTERN PR AS
MENTIONED ABOVE. THE MID LEVEL RELATIVE HUMIDITY IS EXPECTED TO BE
WELL ABOVE NORMAL FROM MIDWEEK ONWARD...WHICH MAY CAUSE MOSTLY
CLOUDY SKIES FROM MIDWEEK INTO THE WEEKEND. HAVING CLOUDY SKIES
WOULD LIMIT DIURNAL HEATING AND SEA BREEZE CONVERGENCE OVER
WESTERN PR. AS ALREADY MENTIONED...THE MID AND UPPER LEVEL
DYNAMICS ARE MORE UNSTABLE ACROSS EASTERN PR INTO THE USVI LATE
THURSDAY INTO FRIDAY.
AT THIS TIME...THE 24-HOUR RAINFALL ACCUMULATION ENDING ON FRIDAY
AT 12Z SUGGESTS RAINFALL AMOUNTS OF 2-4 INCHES WITH ISOLATED
HIGHER AMOUNTS ACROSS EASTERN PR INTO THE USVI...AND GENERALLY
UNDER 1 INCH OF RAIN FOR THE WESTERN HALF OF PR. WHILE THE 3-DAY
RAINFALL ACCUMULATION FORECAST ENDING AT 12Z FRIDAY...SUGGESTS
THAT EASTERN PR INTO THE NORTHERN USVI COULD OBSERVE AS MUCH AS
5-6 INCHES WITH ISOLATED HIGHER AMOUNTS...CONSIDERING THAT THERE
ARE SHOWERS AND THUNDERSTORMS CURRENTLY AFFECTING THOSE AREAS.
CENTRAL TO WESTERN PR...AS WELL AS ST CROIX ARE FORECAST 1-3
INCHES OF RAIN FOR THE 3-DAY ACCUMULATION.
UNCERTAINTY INCREASES FOR THE WEEKEND...AS THE MODEL GUIDANCE
TRIES TO SOLVE THE DEEPENING OF A LOW PRESSURE OVER THE WESTERN
CARIBBEAN...WHICH THE NATIONAL HURRICANE CENTER IS MONITORING FOR
POSSIBLE TROPICAL CYCLONE FORMATION. THE GFS MODEL DEVELOPS A
CLOSED LOW TO THE SOUTH OF HISPANIOLA BY SUNDAY MORNING WITH A SFC
TROUGH EXTENDING INTO THE NORTHEAST CARIBBEAN...WHILE THE ECMWF
HAS A BROADER CIRCULATION FOR THAT TIME FRAME...BUT IT ALSO HAS A
SMALL SECONDARY CIRCULATION STARTING TO DEVELOP NEAR HISPANIOLA
AND PR. FOR THAT REASON...CONFIDENCE IS VERY LOW FOR THE WEEKEND
FORECAST AS IT WILL BE IMPACTED BY THIS DEEPENING LOW. SHOWERS AND
THUNDERSTORMS MAY AFFECT WESTERN PR THIS WEEKEND WITH A SOUTHERLY
LOW-LEVEL FLOW DEPENDING ON HOW THE SFC LOW PRESSURE DEVELOPS AND
MOVES THROUGH THE CARIBBEAN.
ALAMO...WPC (USA)
GALVEZ...WPC (USA)
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