399
FXCA20 KWBC 271243
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
843 AM EDT TUE JUN 27 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUN
27/12UTC: AN UPPER TROUGH CURRENTLY EXTENDING FROM AROUND 26N 64W
INTO HISPANIOLA HAS ITS AXIS JUST EAST OF PR/USVI BUT WILL
RETROGRADE WEST...HAVING ITS AXIS OVER EASTERN HISPANIOLA AND
DIGGING FURTHER SOUTH. THE TRADE WINDS ARE FROM THE EAST WITH
SPEEDS OF 05-15KT. PRECIPITABLE WATER IS NOW ABOVE NORMAL...WITH
VALUES AROUND 2 INCHES BASED ON THE 27/00Z SOUNDING. SATELLITE
IMAGERY SHOWS LITTLE CLOUDINESS THIS MORNING...BUT HIGHER CLOUD
TOPS AND POTENTIAL HEAVIER RAIN IS BEING OBSERVED ACROSS ISOLATED
AREAS IN THE EASTERN CARIBBEAN. A TROPICAL WAVE IS PROPAGATING
NEAR 57W AND TO THE SOUTH OF 16N...WHICH WILL REACH THE LOCAL
AREA ON WEDNESDAY INTO THURSDAY. THIS APPROACHING TROPICAL WAVE
WILL CAUSE A SIGNIFICANT INCREASE IN MOISTURE. A POSITIVE
INTERACTION BETWEEN THE WAVE AND A THE UPPER TROUGH WILL
POTENTIALLY FAVOR MODERATE TO HEAVY PRECIPITATION ON WEDNESDAY AND
THURSDAY.
SIGNIFICANT SHOWER ACTIVITY IS EXPECTED EACH DAY THROUGH THURSDAY.
THE AVAILABLE MOISTURE WILL REMAIN ABOVE NORMAL THROUGH THE REST
OF THE WORKWEEK. PRECIPITABLE WATER VALUES ARE CURRENTLY AT AROUND
2.1 INCHES...WHICH IS ABOVE NORMAL...AND THE LATEST GUIDANCE IS
SUGGESTING FOR THE PRECIPITABLE WATER TO REMAIN BETWEEN 2.0 AND
2.3 INCHES THROUGH FRIDAY...DRYING UP GRADUALLY ON FRIDAY...BUT
MORE SIGNIFICANTLY ON SATURDAY. THE DEEP MOISTURE IN MOISTURE IS
ALSO REFLECTED IN THE MID LEVELS AS WELL...WITH RELATIVE HUMIDITY
REMAINING ABOVE NORMAL THROUGH THE WEEK...PEAKING AT OR ABOVE 2
STANDARD DEVIATIONS HIGHER THAN NORMAL IN THE MID TO LATTER PART
OF THE WEEK. THERE IS A THREAT OF THUNDERSTORMS...BUT THE 500MB
TEMPERATURES ARE EXPECTED TO BE NEAR OR ABOVE NORMAL. THE EGDI
ALGORITHM IS SHOWING THE POTENTIAL FOR SCATTERED THUNDERSTORMS
WITH HEAVY RAIN...BUT THE GR02T ALGORITHM IS INDICATING ONLY A
MARGINAL TO SLIGHT RISK OF SEVERE STORMS.
TODAY...THERE MAY BE A SMALL AMOUNT OF SAHARAN DUST OVER THE
AREA...BUT SHOWERS AND THUNDERSTORMS ARE STILL FORECAST IN THE
AFTERNOON HOURS ACROSS THE INTERIOR TO WESTERN SECTIONS OF
PR...POSSIBLY CAUSING SIGNIFICANT AMOUNTS OF RAIN WITH DECENT
COVERAGE OF RAIN OF OVER AN INCH OF RAIN...WITH ISOLATED AMOUNTS
OF OVER 2 INCHES. EASTERN PR AND THE USVI WILL HAVE A MORE
ADVECTIVE PATTERN WITH SCATTERED BRIEF OVER THE AREA. ON WEDNESDAY
AND THURSDAY...THE TROPICAL WAVE IS EXPECTED TO MOVE IN AND CAUSE
A GENERALIZED RISK FOR SIGNIFICANT SHOWERS AND THUNDERSTORMS.
THERE IS STILL SOME DISCREPANCY AMONG THE MODEL GUIDANCE IN
SHOWING THE AREAS WITH THE HIGHEST AMOUNTS OF RAIN.
HOWEVER...RAINFALL ACROSS MOST OF THE LOCAL ISLANDS CAN BE
EXPECTED. WEDNESDAY MAY HAVE MORE AFTERNOON CONVECTION ACROSS THE
CENTRAL TO WESTERN AND NORTHWESTERN SECTIONS OF PR...BUT EASTERN
PR AND THE USVI ARE EXPECTED TO ALSO HAVE SIGNIFICANT RAINFALL ON
WEDNESDAY AND THURSDAY. MOISTURE AND SHOWER ACTIVITY WILL START TO
DECREASE SLOWLY ON FRIDAY...AS MORE SAHARAN DUST MOVES IN. THE
5-DAY TOTAL RAINFALL FORECAST IS SIGNIFICANT...WITH PORTIONS OF
THE NORTHWESTERN QUADRANT OF PR HAVING OVER 5 INCHES OF
RAIN...EASTERN PR ALSO OVER 5 INCHES...AND THE USVI BETWEEN 1.5
AND 2.25 INCHES.
ALAMO/GALVEZ/ACOSTA...WPC (USA)
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