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Tropical Discussion
 
(Latest Discussion - Issued 1047Z May 24, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
647 AM EDT THU MAY 24 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM MAY 25/06
UTC: MID/UPPER LEVEL RIDGE OVER THE WESTERN ATLANTIC CONTINUES TO
WEAKEN UNDER PRESSURE FROM POLAR TROUGH TO THE NORTH. AS THE RIDGE
FLATTENS...A TUTT TO THE EAST OF THE ISLANDS IS GRADUALLY PULLING
TO THE NORTHEAST. ALTHOUGH THE RIDGE TENDS TO WEAKEN...ASSOCIATED
TRADE WINDS CAP CONTINUES TO HOLD. THIS IS TRAPPING SHALLOW
MOISTURE IN ATMOSPHERE BELOW 700 HPA. AT LOW LEVELS...BROAD RIDGE
OVER THE CENTRAL ATLANTIC FAVORS AN EAST-SOUTHEASTERLY FLOW ACROSS
THE FORECAST AREA. THIS IS ADVECTING SHALLOW MOISTURE ACROSS THE
LEEWARD ISLES THAT CONTINUES TO POOL OVER PUERTO RICO AND THE
VIRGIN ISLES. THIS...HOWEVER...IS NOT AS HIGH AS THE GFS
PREVIOUSLY ANTICIPATED.

MID LEVEL RIDGE PATTERN IS TO REMAIN ILL ORGANIZED DURING THE NEXT
DAY OR SO. DURING THE WEEKEND...AS A TROUGH DEEPENS ACROSS THE
GULF OF MEXICO...THE RIDGE IS TO THEN BUILD ONCE AGAIN FROM THE
EASTERN CARIBBEAN NORTHWARD TO THE WESTERN ATLANTIC. THIS WILL
HELP SUSTAIN...IF NOT STRENGTHEN...THE TRADE WINDS CAP ENVELOPING
THE FORECAST AREA. LOW LEVEL FLOW IS TO REMAIN NEARLY UNCHANGED
DURING THE WEEKEND...WITH BROAD RIDGE PATTERN OVER THE BASIN
FAVORING AN EAST-SOUTHEASTERLY FLOW ACROSS THE FORECAST AREA. AS
THE PATTERN HOLDS...PWAT CONTENT IS TO GRADUALLY INCREASE TO
AROUND 30-35MM LATER DURING THE WEEKEND...TO FAVOR A GRADUAL
INCREASE IN DIURNAL CONVECTION. MOST ACTIVE IS EXPECTED ACROSS
NORTHWEST AND INTERIOR PORTIONS OF PUERTO RICO IN LATE MORNING TO
AFTERNOON CONVECTION...WITH A SECONDARY MAXIMA BETWEEN EL YUNQUE
AND THE SAN JUAN METRO AREA. A SLIGHT INCREASE IS POSSIBLE DURING
THE WEEKEND AS DEEPER MOISTURE ADVECTS ACROSS THE FORECAST AREA.
ALTHOUGH MODELS AGREE IN PEAK IN INSTABILITY ON SUNDAY...THEY HAVE
BEEN SLOW TO RESPOND TO MORE FAVORABLE ENVIRONMENTAL CONDITIONS.

DURING THE MEDIUM RANGE PERIOD...AS THE MID/UPPER LEVEL RIDGE
STRENGTHENS OVER THE WESTERN ATLANTIC...A TUTT IS TO AMPLIFY.
EARLY NEXT WEEK THE TROUGH IS TO EXTEND INTO THE NORTHEAST
CARIBBEAN...WHERE IT IS TO THEN FOCUS SHORT WAVE ENERGY AND A
SUBTROPICAL JET MAXIMA. IF THIS EVOLVES AS THE MODELS
SUGGEST...CONVECTION ACROSS THE FORECAST AREA COULD BECOME MORE
ACTIVE/BETTER ORGANIZED. NOTE THAT THE CFS FORECAST DURING THIS
PERIOD STILL SHOWS POSSIBILITY OF AN ATMOSPHERIC KELVIN WAVE
STREAMING ACROSS THE CARIBBEAN BASIN...WHICH COULD PROVIDE FURTHER
ENHANCEMENT TO CONVECTIVE DEVELOPMENT.

DAVISON...WPC (USA)