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FXCA20 KWBC 051225
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
824 AM EDT WED JUL 05 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUL
05/12UTC: SAHARAN DUST WILL BE PRESENT ACROSS THE LOCAL ISLANDS
TODAY AND THURSDAY...BRINGING DRY AIR AND LIMITING SHOWER
ACTIVITY. SURFACE HIGH PRESSURE ACROSS THE CENTRAL TO EAST CENTRAL
ATLANTIC WILL KEEP AN EAST TO EAST SOUTHEAST WIND FLOW FOR THE
NEXT SEVERAL DAYS ACROSS THE LOCAL ISLANDS. A MID-LEVEL HIGH
PRESSURE WILL MEANDER OVER THE SOUTHWESTERN ATLANTIC...JUST NORTH
OF PR INTO THE BAHAMAS...FROM TODAY INTO THE WEEKEND. THERE WILL
ALSO BE A TRADE WIND INVERSION AT AROUND THE 850 HPA LEVEL TODAY
INTO THURSDAY. AN UPPER-LEVEL LOW TO THE NORTH OF PUERTO
RICO...AT AROUND 26N AND 65W IS EXPECTED TO MOVE EAST OVER THE
NEXT 3 DAYS. HOWEVER...AFTER THAT...THE 00Z GFS MODEL RUN STARTS
MOVING THE UPPER LOW TO THE SOUTHWEST INTO HISPANIOLA BY EARLY
NEXT WEEK...WHILE THE ECMWF AND JUST ABOUT ALL OTHER GLOBAL MODELS
KEEP THE UPPER LOW AND ASSOCIATED TROUGH SLOWLY MOVING EAST ACROSS
THE TROPICAL ATLANTIC TO THE EAST NORTHEAST OF THE CARIBBEAN. THE
POSITIONING OF THIS UPPER TROUGH CAN BE IMPORTANT BECAUSE THERE IS
A TROPICAL WAVE APPROACHING ON SUNDAY INTO MONDAY...WHICH COULD
INTERACT WITH THE UPPER LOW AND CAUSE SIGNIFICANT SHOWER ACTIVITY
ACROSS THE LOCAL ISLANDS IF THE POSITIONING AND TIMING ARE
ADEQUATE. THAT SAID...GIVEN THAT THE GFS MODEL IS AN OUTLIER...OUR
FORECAST REFLECTS A PREFERENCE FOR THE GENERAL CONSENSUS OF THE
GLOBAL MODELS...KEEPING THE UPPER TROUGH FURTHER EAST AND HAVING
MORE MODEST AMOUNTS OF RAINFALL LATER IN THE FORECAST PERIOD. THE
APPROACHING TROPICAL WAVE WILL STILL CAUSE AN INCREASE IN MOISTURE
AND SHOWERS ON SUNDAY INTO MONDAY...THOUGH NOT QUITE AS MUCH AS IF
IT HAD UPPER LEVEL SUPPORT.
WITH THE EXPECTED SAHARAN DUST...THE OVERALL AVAILABLE MOISTURE
WILL BE SLIGHTLY BELOW NORMAL TODAY AND THURSDAY...WITH
PRECIPITABLE WATER VALUES BETWEEN 1.4 AND 1.6 INCHES. MOISTURE
WILL INCREASE GRADUALLY ON FRIDAY...CAUSING PRECIPITABLE WATER TO
INCREASE TO NEAR 1.9 INCHES...BUT WILL DECREASE AGAIN ON SATURDAY
TO 1.4 INCHES. THE ARRIVAL OF THE TROPICAL WAVE ON SUNDAY WILL
CAUSE THE MOISTURE TO INCREASE TO ABOVE NORMAL FROM SUNDAY INTO
MONDAY...PRECIPITABLE WATER MAXING OUT NEAR 2.2 INCHES.
FOR TODAY AND THURSDAY...THE FORECAST SUGGESTS A RELATIVELY DRY
AND HAZY COUPLE OF DAYS. SOME ISOLATED SHOWER ACTIVITY IN THE
NIGHTTIME AND EARLY MORNING HOURS COULD AFFECT THE USVI AND
EASTERN PR...WHILE BRIEF AFTERNOON CONVECTION COULD AFFECT
ISOLATED SPOTS OF WESTERN PR. THE INCREASE IN MOISTURE AND
DECREASE OF SAHARAN DUST WOULD ALLOW FOR A MORE TYPICAL RAINFALL
PATTERN ON FRIDAY AND SATURDAY...WITH SCATTERED SHOWERS ACROSS THE
USVI AND EASTERN PR IN THE NIGHT AND EARLY MORNING HOURS...WHILE
LOCALLY INDUCED SHOWERS ARE FORECAST ACROSS WESTERN PR.
HOWEVER...SLIGHTLY NORTHEASTERLY WINDS COULD CAUSE THE AFTERNOON
CONVECTION ACROSS THE SOUTHWESTERN QUADRANT OF PR ON SATURDAY. THE
EXPECTED TROPICAL WAVE ON SUNDAY WILL CAUSE AN INCREASE IN SHOWER
ACTIVITY. HOWEVER...GIVEN THE AFOREMENTIONED DISCREPANCY AMONG THE
GFS AND THE OTHER GLOBAL MODELS...CONFIDENCE IS LOWER THAN NORMAL
FOR THE RAINFALL FORECAST FROM SUNDAY INTO EARLY MONDAY. THAT
SAID...THERE IS AGREEMENT THAT THE TROPICAL WAVE WILL BE MOVING
IN...AND WILL CAUSE AN INCREASE IN SHOWER ACTIVITY ACROSS THE USVI
AND EASTERN PR.
THE 5-DAY RAINFALL TOTALS ARE FORECAST TO BE NEAR 1.75 TO 2 INCHES
ACROSS EASTERN PR...JUST OVER 1 INCH ACROSS WEST TO NORTHWESTERN
PR...AND NEAR 0.50 TO 0.75 INCHES FOR THE USVI. SUNDAY INTO MONDAY
IS EXPECTED TO BE THE RAINIEST PERIOD IN THE NEXT 5 DAYS DUE TO
THE ARRIVAL OF THE TROPICAL WAVE.
ALAMO/GALVEZ...WPC (USA)
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