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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1047Z Mar 27, 2015)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
647 AM EDT FRI MAR 27 2015

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. HIGHLY
AMPLIFIED SINUSOIDAL WAVE PATTERN DOMINATES THE MID/UPPER LEVEL OF
THE ATMOSPHERE...WITH A RIDGE OVER THE CARIBBEAN/WESTERN ATLANTIC
SEPARATING TWO TROUGHS. THE WESTERNMOST DOMINATES THE CENTRAL
USA...WHILE THE ONE TO THE EAST BOUNDS BETWEEN 60W-30W. AT LOW
LEVELS...UNDER INFLUENCE OF THESE FEATURES...A BROAD RIDGE EXTENDS
ACROSS THE WESTERN ATLANTIC...WITH A POLAR FRONT STRETCHING ALONG
THE EASTERN FRINGES OF THIS RIDGE WHILE REMAINING FAR TO THE
NORTH. OVER THE BASIN...BROAD RIDGE TO THE NORTH SUSTAINS A TIGHT
PRESSURE GRADIENT...AND BRISK EASTERLY TRADES ACROSS THE ISLAND
CHAIN-FORECAST AREA. THIS...IN-TURN...FAVORS GENERATION OF
STREAMERS AND LIGHT TRADE WIND SHOWERS ACROSS THE VIRGIN ISLES TO
EASTERN PORTIONS OF PUERTO RICO.

MID/UPPER LEVEL FLOW PATTERN IS TO GRADUALLY EVOLVE DURING THE
WEEKEND...WITH RIDGE EXPECTED TO FLATTEN LATER ON SUNDAY/EARLY
MONDAY MORNING AS TROUGH OVER NORTH AMERICA LIFTS OVER THIS AXIS.
SUCCESSIVE MID LEVEL PERTURBATIONS ARE TO THEN STREAM ACROSS THE
BAHAMAS-NORTHERN CARIBBEAN ISLES THROUGH THE MIDDLE OF NEXT WEEK.
AS THE MID LEVEL RIDGE WEAKENS... EXPECTING TRADE WINDS CAP TO
GRADUALLY LIFT FROM 750/800 TO 600 HPA EARLY NEXT WEEK. ALTHOUGH
THE CAP LIFTS...FORECASTED PWAT AMOUNTS REMAIN SURPRISINGLY LOW.
CONSIDERING INFLOW OF SHORT WAVE ENERGY AND WEAKENING OF CAP
INVERSION WE WERE EXPECTING AN INCREASE IN PWAT AMOUNTS EARLY NEXT
WEEK. SO NEED TO KEEP AN EYE ON THIS TO SEE HOW FUTURE MODEL RUNS
RESPOND TO EVOLVING MESO-SYNOPTIC PATTERN. AT LOW LEVELS...THE
SURFACE RIDGE PATTERN IS FORECAST TO ALSO WEAKEN...WITH PRESSURE
GRADIENT TO SLACKEN THROUGH SATURDAY AFTERNOON. TRADES ARE TO
DECREASE FROM 20-25KT TO 10-15KT LATER IN THE WEEKEND.
MEANWHILE...PESTERING TRADE WIND SHOWERS ARE EXPECTED TO AFFECT
THE VIRGIN ISLES-EASTERN PUERTO RICO AND THE SAN JUAN METRO
AREA...WITH AFTERNOON CONVECTION TO CLUSTER OVER WESTERN INTERIOR
PORTIONS OF THE ISLAND. AS THE GRADIENT SLACKENS AND THE TRADES
WEAKEN LATER ON SATURDAY THE INCIDENCE OF STREAMERS/TRADE WIND
SHOWERS IS TO DECREASE...BUT SEA/LAND BREEZE CONVERGENCE IS MORE
LIKELY TO BECOME A PROBLEM. MOST ACTIVE CONVECTION IS EXPECTED
ACROSS CENTRAL-WESTERN PORTIONS OF PUERTO DURING THE AFTERNOON
HOURS STARTING ON SUNDAY AND PERSISTING...IF NOT
INCREASING...THROUGH THE MIDDLE OF NEXT WEEK.

CRAIG...TTMS (TRINIDAD AND TOBAGO)
NANDA...MDS (SURINAME)
DAVISON...WPC (USA)