707
FXCA20 KWBC 041252
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
852 AM EDT TUE APR 04 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR
04/12UTC: THE RAINFALL ACTIVITY IS EXPECTED TO INCREASE
SIGNIFICANTLY THIS WEEK...WITH WEDNESDAY AND THURSDAY BEING THE
DAYS WITH HIGHEST RAIN ACCUMULATIONS DUE TO A COMBINATION OF
INCREASED MOISTURE AND INSTABILITY IN THE MID AND UPPER LEVELS. IN
THE UPPER LEVELS...A TROUGH THAT EXTENDS FROM THE BERMUDA REGION
SOUTH INTO CENTRAL VENEZUELA WILL AMPLIFY AND STRENGTHEN OVER THE
NEXT COUPLE OF DAYS. ITS AXIS WILL BE JUST WEST OF PUERTO
RICO...BY THURSDAY IT COULD BE AN UPPER LOW. THIS UPPER LEVEL
TROUGH IS ALSO ASSOCIATED WITH A DEVELOPING MID-LEVEL TROUGH THAT
COULD HAVE ITS AXIS JUST OVER PR/USVI BY WEDNESDAY...AND IS ALSO
STRENGTHENING. BECAUSE THESE TROUGHS ARE CURRENTLY RELATIVELY
WEAK...THE IMPACT IS NOT EXPECTED TO BE TOO SIGNIFICANT TODAY OVER
PR/USVI AND THE REST OF THE NORTHEAST CARIBBEAN. THERE IS ALSO
BELOW NORMAL MOISTURE OVER THE AREA TODAY...WITH THE PRECIPITABLE
WATER OVER PR NEAR 1 INCH THIS MORNING...THOUGH EXPECTED TO
GRADUALLY INCREASE THROUGH THE DAY. FOR TODAY...SCATTERED SHOWERS
ARE EXPECTED ACROSS EASTERN PR AND USVI...ESPECIALLY IN THE
MORNING...WHILE AFTERNOON SHOWERS AND ISOLATED THUNDERSTORMS COULD
AFFECT WESTERN PR IN THE AFTERNOON...POSSIBLY CAUSING UP TO AN
INCH OF RAIN OR SO ACROSS SOME AREAS.
THE DEVELOPMENT OF THE MID AND UPPER LEVEL TROUGHS IS FORECAST TO
CAUSE A SIGNIFICANT INCREASE IN SHOWER ACTIVITY ACROSS PR/USVI ON
WEDNESDAY AND THURSDAY. NOT ONLY THAT...BUT ALSO THE PRECIPITABLE
WATER WILL INCREASE GRADUALLY TO THE UPPER END OF NORMAL
LEVELS...WITH VALUES EASILY REACHING 1.6 INCHES ON WEDNESDAY AND
THURSDAY. THE MID LEVEL RELATIVE HUMIDITY WILL INCREASE TO OVER 2
STANDARD DEVIATIONS ABOVE NORMAL...THE MID LEVEL TEMPERATURES WILL
DROP TO TO BELOW -10C...SPECIFICALLY -12C ACCORDING TO BOTH THE
ECMWF AND THE GFS. THIS STRONG UPPER LOW/TUTT IS FORECAST TO
CENTER OVER THE MONA PASSAGE BY THURSDAY...WHICH IS IDEAL FOR
INCREASED INSTABILITY ACROSS PR/USVI. THE STRONG TROUGH WILL HAVE
A REFLECTION IN THE MID-LEVELS...AND INDUCE A PERTURBATION IN THE
TRADES. IN ADDITION TO THAT...IT COINCIDES WITH THE ARRIVAL OF THE
UPPER DIVERGENT/WET PHASE OF THE MJO AND A TROPOSPHERIC KELVIN
WAVE. THEREFORE...THE COMBINATION OF THESE FACTORS SUGGEST THE
POTENTIAL FOR MODERATE TO LOCALLY HEAVY RAINFALL FROM WEDNESDAY
THROUGH FRIDAY...LIKELY PEAKING ON THURSDAY.
IN TERMS OF FORECAST AMOUNTS...TODAY...JUST OVER A HALF AN INCH OF
RAIN IS FORECAST ACROSS NORTHEAST PR AND WESTERN PR WITH A FEW
HUNDREDTHS ACROSS THE USVI. WEDNESDAY AND THURSDAY INTO EARLY
FRIDAY...DUE TO THE EXPECTED WET SPELL...MODELS ARE IN VERY GOOD
AGREEMENT THAT NORTHEAST PUERTO RICO AND THE NORTHERN USVI WILL
ALSO SEE A SIGNIFICANT INCREASE IN SHOWER ACTIVITY...WITH MAXIMAS
OF OVER AN INCH TO ALMOST 2 INCHES OF RAIN ACROSS NORTHEAST
PR...AND FROM ABOUT 0.4 INCHES ON WEDNESDAY TO ABOUT 1.5 INCHES OF
RAIN ON THURSDAY AND FRIDAY ACROSS THE USVI. ON WEDNESDAY AND
THURSDAY...EXPECT MODERATE TO LOCALLY HEAVY RAINFALL WITH A FEW
THUNDERSTORMS ACROSS WESTERN PR. OVER 1 INCH OF RAIN IS EXPECTED
IN GENERAL...BUT 1-3 INCHES OF RAIN ACROSS ISOLATED AREAS WILL NOT
BE RULED OUT. ON FRIDAY...AS THE BULK OF THE ACTIVITY DRIFTS
NORTHWARD AIDED BY THE UPPER TROUGH...EXPECT A DECREASING TREND
STARTING IN THE EARLY AFTERNOON. HOWEVER...ENHANCED TRADE WIND
CONVERGENCE WILL STILL FAVOR CONVECTION IN THE NORTHERN VI AND
COASTAL NORTHEAST PR...WHERE EXPECT MAXIMA OF 1-2 INCHES. NOTE
THAT A STRONG GRADIENT IS FORECAST BETWEEN SAN JUAN AND FAJARDO.
FIVE DAY TOTALS ACROSS NORTHEAST PR ARE FORECAST TO EXCEED 4
INCHES...WHILE IN THE SAN JUAN METRO WE EXPECT TOTALS OF 0.5-1.5
INCHES. ACROSS WESTERN PR...THE 5-DAY TOTALS ARE FORECAST TO
EXCEED 3 INCHES...BUT HIGHER AMOUNTS ARE POSSIBLE ACROSS ISOLATED
AREAS.
ALAMO/ACOSTA...WPC (USA)
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