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FXCA20 KWBC 181247
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
847 AM EDT FRI AUG 18 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM AUG
18/12UTC: SAHARAN DUST PARTICLES ARE EXPECTED TO CONTINUE ACROSS
PR/USVI TODAY AND SATURDAY. ALTHOUGH THE SAHARAN DUST
CONCENTRATION WILL DECREASE SIGNIFICANTLY ON SUNDAY...SOME
INCREASE IN CONCENTRATION IS EXPECTED ON MONDAY INTO
TUESDAY...THOUGH NOT MUCH. THE AVAILABLE MOISTURE WILL BE ABOVE
NORMAL TODAY...BECOMING NEAR NORMAL ON SATURDAY AND SUNDAY...THEN
SLIGHTLY BELOW NORMAL EARLY ON MONDAY BEFORE INCREASING TO ABOVE
NORMAL LEVELS BY TUESDAY...DUE TO A POSSIBLE STRONG TROPICAL WAVE
APPROACHING THE ISLANDS. THIS TROPICAL WAVE IS BEING MONITORED BY
THE NATIONAL HURRICANE CENTER...HAVING A LOW CHANCE OF DEVELOPING
INTO A TROPICAL CYCLONE THROUGH 7 DAYS AS OF THIS WRITING.
HOWEVER...THE NATIONAL HURRICANE CENTER SUGGESTED THAT AN AREA OF
LOW PRESSURE COULD DEVELOP IN A DAY OR TWO...THOUGH THERE WAS NO
MENTION OF A TROPICAL CYCLONE BEING DEVELOPED IN THAT TIME FRAME.
A SURFACE HIGH PRESSURE ACROSS THE CENTRAL ATLANTIC WILL DOMINATE
FOR THE NEXT SEVERAL DAYS...KEEPING EASTERLY WINDS ACROSS PR/USVI
INTO EARLY NEXT WEEK. HOWEVER...THE APPROACHING TROPICAL WAVE ON
TUESDAY WILL CAUSE A SHIFT IN THE LOCAL WINDS ON MONDAY INTO
TUESDAY. IN THE UPPER LEVELS...A TUTT ACROSS THE CENTRAL CARIBBEAN
CONTINUES MOVING WEST...REACHING THE WESTERN CARIBBEAN AND GULF OF
MEXICO BY MONDAY. MEANWHILE ANOTHER TUTT WILL DEVELOP TO THE NNE
OF PR ACROSS THE WEST CENTRAL TROPICAL ATLANTIC...WITH A TILTED
TROUGH AXIS OVER PR...CAUSING SOME INSTABILITY ACROSS THE LOCAL
ISLANDS FROM SUNDAY THROUGH TUESDAY. THIS TUTT AND ASSOCIATED
TROUGH MAY COINCIDE WITH THE APPROACHING TROPICAL WAVE...THOUGH AT
THE MOMENT THE LATEST GUIDANCE IS SUGGESTING THE HIGHEST MOISTURE
OF THE TROPICAL WAVE ON TUESDAY...WHEN THE TUTT IS NOT IN THE MOST
FAVORABLE POSITION. HOWEVER... NOT ONLY ARE THE 700 AND 500MB
VORTICITY INCREASING MONDAY INTO TUESDAY...WHILE THE TROPICAL WAVE
APPEARS TO HAVE SIGNIFICANT MOISTURE...BUT THERE IS STRONG
DIVERGENCE ALOFT JUST EAST OF PR...WHICH NORMALLY FAVORS
PERSISTENT SHOWER AND THUNDERSTORM DEVELOPMENT. GIVEN THE LOCATION
OF THE DIVERGENCE...THE USVI WOULD HAVE A GOOD CHANCE OF
SHOWERS...AS WELL AS PORTIONS OF SOUTHERN AND EASTERN PR. THE EGDI
ALGORITHM DOES SUGGEST SCATTERED THUNDERSTORMS OVER THE LOCAL AREA
FOR TUESDAY...BUT WITH THE STRONGEST DIVERGENCE ACROSS THE USVI.
FOR TODAY...THE TOTAL RAINFALL FORECAST IS AROUND 0.5 INCH ACROSS
EAST AND NORTHEAST PR SA WELL AS WESTERN PR. BETWEEN A TENTH AND A
QUARTER OF AN INCH FOR THE USVI. THE 5-DAY TOTAL RAINFALL FORECAST
IS AROUND 3.5 TO 4 INCHES OF RAIN FOR EAST/NORTHEAST PR...NEAR 1.5
INCHES FOR WESTERN PR...AND BETWEEN 2 AND 3 INCHES FOR THE USVI.
ALAMO/ACOSTA...WPC (USA)
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