TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
656 AM EDT FRI MAY 25 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM MAY 25/06
UTC: DIGGING MID/UPPER LEVEL TROUGH OVER THE GULF OF MEXICO IS TO
INDUCE THE NORTHWARD AMPLIFICATION OF A RIDGE FROM THE CENTRAL
CARIBBEAN TO THE WESTERN ATLANTIC. AS THE RIDGE BUILDS...MODELS
NOW AGREE ON A FAIRLY STRONG TRADE WINDS CAP TO ESTABLISH ACROSS
THE NORTHEAST CARIBBEAN ISLANDS EARLY IN THE CYCLE. THE INVERSION
IS FORECAST TO DROP FROM AROUND 650/700 HPA EARLY TODAY TO AROUND
750 HPA BY MIDDAY ON SATURDAY. AT LOW LEVELS...BROAD RIDGE OVER
THE ATLANTIC BASIN FAVORS A BRISK EAST-SOUTHEAST FLOW ACROSS THE
NORTHEAST CARIBBEAN. THIS IS ADVECTING SHALLOW MOISTURE ACROSS THE
ISLAND CHAIN TO PUERTO RICO-VIRGIN ISLES...WHERE IT IS TO FEED
DIURNAL CONVECTION. ACROSS THE VIRGIN ISLES...DAYTIME STREAMERS
ARE TO SUSTAIN MOSTLY LIGHT RAINFALL AMOUNTS IN PASSING SHOWERS.
MEASURABLE AMOUNTS ARE EXPECTED OVER PUERTO RICO...WITH MAXIMA
CLUSTERING ACROSS INTERIOR/NORTHWEST PORTIONS OF THE ISLAND IN
AFTERNOON CONVECTION. HEAVIEST AMOUNTS ARE EXPECTED AROUND
MOCA-AGUADA-RINCON. IN BRISK EASTERLY TRADES...ECHO TRAINING IS
EXPECTED DOWNSTREAM FROM EL YUNQUE TO PORTIONS OF THE SAN JUAN
METRO AREA...TO AFFECT PORTIONS OF CAROLINA-SAN JUAN-BAYAMON TO
NAME A FEW...WITH LOCALIZED MAXIMA PEAKING AT NEARLY AN INCH. ON
SATURDAY...AS THE TRADE WINDS CAP STRENGTHENS...EXPECTING A SLIGHT
DECREASE IN ACTIVITY.

ON SUNDAY-MONDAY SYNOPTIC PATTERN IS TO CHANGE. AS THE MID LEVEL
RIDGE STRENGTHENS ITS FOOTHOLD OVER THE WESTERN ATLANTIC...IT IS
TO THEN INDUCE THE SOUTHWARD AMPLIFICATION OF A TROUGH ACROSS THE
NORTHEAST CARIBBEAN. THIS FEATURE IS TO BECOME THE DOMINANT
FEATURE EARLY NEXT WEEK AS IT EVOLVES INTO A CLOSED TUTT LOW TO
THE NORTHEAST OF THE LEEWARD ISLES. AS THE BASE OF THE TROUGH
MEANDERS OVER THE NORTHEAST CARIBBEAN...GLOBAL MODELS SHOW A JET
MAXIMA ROUNDING THE BASE OF THE TROUGH LATER DURING THE
WEEKEND/EARLY NEXT WEEK...TO RESULT IN PERIODS OF ENHANCED UPPER
DIVERGENCE. SUNDAY IN PARTICULAR LOOKS LIKE THE MOST FAVORABLE FOR
DEEP CONVECTION TO DEVELOP...AS THIS IS TO COINCIDE WITH INFLOW OF
MID LEVEL CYCLONIC VORTICES ACROSS THE FORECAST AREA. AT LOW
LEVELS...TROPICAL WAVE STREAMING ACROSS THE ISLAND CHAIN EARLY ON
SUNDAY MORNING IS TO ADVECT A PLUME OF DEEPER MOISTURE ACROSS THE
VIRGIN ISLES TO PUERTO RICO DURING THE DAY. BOTH THE GFS AND ECMWF
RESPOND TO THIS...SHOWING WIDESPREAD CONVECTION GRADUALLY BUILDING
FROM THE EAST...WITH PEAK IN ACTIVITY ACROSS PUERTO RICO DURING
THE AFTERNOON HOURS ON SUNDAY. AS A RESULT...NOW SHOWING LOCALLY
HEAVY RAINFALL AMOUNTS OVER NORTHWEST PUERTO RICO/GUAJATACA BASIN
DURING THE MID-LATE AFTERNOON HOURS. ON MONDAY...TRAILING MOISTURE
IS TO FAVOR A SECOND ROUND OF CONVECTION. BUT AS UPPER SUPPORT
WANES...IT IS LIKELY TO ONLY FAVOR MODERATE RAINFALL AMOUNTS.

NOTE TO ALL USERS...UNLESS OTHERWISE REQUESTED BY THE SAN JUAN
FO...DUE TO THE MEMORIAL DAY HOLIDAY THIS PRODUCT WILL NOT BE
UPDATED UNTIL TUESDAY MAY 29.

DAVISON...WPC (USA)