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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1158Z Feb 22, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
658 AM EST THU FEB 22 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM FEB 22/06
UTC: A MID/UPPER LEVEL TROUGH EXTENDS OVER THE NORTHERN CARIBBEAN
ISLES...WITH AXIS SEPARATING A CELL OF THE SUBTROPICAL RIDGE TO
THE NORTH FROM A CELL OF THE SUBEQUATORIAL RIDGE TO THE SOUTH. AT
LOW LEVELS...BROAD RIDGE REMAINS THE DOMINANT FEATURE ACROSS THE
WESTERN ATLANTIC-NORTHERN CARIBBEAN. THIS FAVORS A FRESH
NORTHEASTERLY FLOW ACROSS THE FORECAST AREA. THIS DROVE A SAGGING
FRONT ACROSS THE NORTHERN LEEWARD ISLES INTO THE NORTHEAST
CARIBBEAN. FORECAST AREA LIES ON THE DRY SIDE OF THIS
BOUNDARY...WITH SATELLITE DERIVED PWAT ANALYSIS SHOWING A PWAT
MINIMA ENVELOPING PUERTO RICO AND THE VIRGIN ISLES.

CONSISTENT WITH PREVIOUS FORECASTS...EXPECTING MID/UPPER LEVEL
PATTERN TO GRADUALLY EVOLVE UNDER INFLUENCE OF BUILDING CELL OF
THE SUBEQUATORIAL RIDGE TO THE SOUTH. AS THE RIDGE
STRENGTHENS...IT WILL DISPLACE THE TROUGH TO THE NORTH AND
WEST...WITH ASSOCIATED JET MAXIMA GRADUALLY LIFTING FROM THE
FRENCH ISLES TO THE NORTHEAST CARIBBEAN AS THE WEEK WEARS ON. AS
THE JET RELOCATES ACROSS THE FORECAST AREA...AN UPPER DIVERGENT
PATTERN IS TO ESTABLISH BETWEEN 300-400 HPA...WHILE ABOVE 300 HPA
A CONVERGENT PATTERN IS TO PERSIST. THIS...HOWEVER...TENDS TO
WEAKEN ON SATURDAY-SUNDAY. AS A RESULT...ENVIRONMENTAL CONDITIONS
ARE TO BECOME SOMEWHAT MORE FAVORABLE FOR DEEP CONVECTION TO
DEVELOP LATER DURING THE WEEKEND. AT MID LEVELS...RETROGRESSING
TUTT LOW PULLS ACROSS THE FORECAST AREA ON FRIDAY-SATURDAY...TO
FAVOR CYCLONIC VORTICITY ADVECTION AS IT MEANDERS ACROSS THE
FORECAST AREA. THE STRONGEST VORTICITY...HOWEVER...IS EXPECTED ON
FRIDAY WHEN BOTH THE GFS AND ECMWF SHOW A RELATIVELY STRONG VORTEX
RAMMING ACROSS THE FORECAST AREA. ENOUGH RESIDUAL ENERGY IS TO
PERSIST TO PROVIDE SOME ENHANCEMENT TO DIURNAL CONVECTION DURING
THE WEEKEND/EARLY NEXT WEEK. AT LOW LEVELS...A CLOSED HIGH TO THE
WEST-SOUTHWEST OF BERMUDA IS TO ANCHOR A BROAD RIDGE OVER THE
WESTERN ATLANTIC THROUGHOUT THE WEEKEND. THIS IS TO FAVOR BRISK
EASTERLY TRADES...WITH WINDS TO PEAK AT 25-30KT DURING THE NEXT
48-60 HRS. ON SATURDAY-SUNDAY THE GRADIENT STARTS TO
SLACKEN...WITH WINDS DECREASING TO 15-20KT. THE PWAT MINIMA
ENVELOPING THE FORECAST AREA IS TO GRADUALLY YIELD TO A MOISTER
AIR MASS LATER TODAY/EARLY MORNING ON FRIDAY...WITH PWAT CONTENT
TO INCREASE TO 1.0-1.25 INCHES...AND IT COULD REACH 1.50 INCHES
DURING THE WEEKEND AS LIGHTER WINDS AND DEEPER INSTABILITY ENVELOP
THE FORECAST AREA. THIS IS REFLECTED IN THE GFS GDI
FORECAST...WITH MODEL SHOWING A HIGHER RISK OF SHOWERS WITH
EMBEDDED THUNDERSTORMS TO DEVELOP LATER DURING THE WEEKEND TO
EARLY NEXT WEEK. FRONTAL BOUNDARY TO THE SOUTH IS TO FRONTOLIZE
EARLY IN THE CYCLE...WITH A WEAK COOL ADVECTIVE PATTERN EXPECTED
OVER THE NEXT TWO DAYS.

AS THE AIR MASS GROWS UNSETTLED...EXPECTING A GRADUAL INCREASE IN
CONVECTION ACROSS THE ENTIRE FORECAST AREA. OVERALL EXPECTING
MODERATE RAINFALL AMOUNTS...WITH LOCALIZED MAXIMA OF 2-3 INCHES
HIGHLY PROBABLE ON SUNDAY-MONDAY TO CLUSTER ACROSS WESTERN
INTERIOR PORTIONS OF PUERTO RICO.

DAVISON/GALVEZ...WPC (USA)