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Tropical Discussion
 
(Latest Discussion - Issued 1157Z Feb 23, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
657 AM EST FRI FEB 23 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM FEB 23/06
UTC: AT UPPER LEVELS...A BUILDING CELL OF THE SUBEQUATORIAL RIDGE
OVER NORTHERN SOUTH AMERICA/ TROPICAL ATLANTIC IS DISPLACING A
TUTT LOW ACROSS THE NORTHEAST CARIBBEAN ISLES. AT LOW
LEVELS...BROAD RIDGE DOMINATES THE FLOW ACROSS THE WESTERN
ATLANTIC...WITH AXIS FAVORING A BRISK NORTHEASTERLY FLOW AND A
COOL ADVECTIVE PATTERN ACROSS THE FORECAST AREA.
THIS...IN-TURN...FAVORS THE GENERATION OF SHALLOW CONVECTION THAT
PESTERS THE VIRGIN ISLES-PUERTO RICO FROM
TIME-TO-TIME...TRIGGERING LIGHT RAINFALL AMOUNTS IN PASSING
SHOWERS.

EARLY IN THE CYCLE...THE BUILDING SUBEQUATORIAL RIDGE DISPLACES
THE TUTT LOW FARTHER TO THE WEST-NORTHWEST...NEARING THE TURKS AND
CAICOS/SOUTHEAST BAHAMAS EARLY ON SATURDAY. A SUBTROPICAL JET
MAXIMA BOUNDS THE EASTERN FRINGES OF THIS TROUGH. THE JET IS TO
ALSO LIFT ACROSS THE FORECAST AREA DURING THE WEEKEND...WITH THE
JET MAXIMA MOVING JUST NORTH OF PUERTO RICO ON SATURDAY AFTERNOON.
THE FORECAST AREA WILL THEN REMAIN ON ITS RIGHT ENTRANCE REGION
THROUGH AT LEAST TUESDAY MORNING. THIS IS TO FAVOR AN UPPER
DIVERGENT LAYER BETWEEN 300-400 HPA. THIS IS TO VENT CONVECTIVE
DEVELOPMENT DURING THE WEEKEND. THE GLOBAL MODELS AGREE ON THE
CORRESPONDING MID LEVEL TROUGH TO MEANDER OVER THE FORECAST AREA
DURING THE NEXT 72-96 HRS. THIS FEATURE SUSTAINS STRONG CYCLONIC
VORTICITY ADVECTION EARLY IN THE CYCLE...WITH WEAKER ADVECTION TO
THEN PERSIST THROUGH THE WEEKEND TO EARLY NEXT WEEK. THE COLD CORE
MID/UPPER LEVEL TROUGH IS TO ALSO DESTABILIZE THE LAYER...WITH THE
GFS GDI FORECAST FOR THE PERIOD STILL SHOWING POTENTIAL FOR RAIN
SHOWERS WITH EMBEDDED THUNDERSTORMS ON SUNDAY AND MONDAY.
IT...HOWEVER...NOW SHOWS MOST UNSTABLE ACROSS SAINT CROIX AND
CARIBBEAN COASTAL WATERS OF PUERTO RICO.

AT LOW LEVELS...BROAD RIDGE IS TO REMAIN THE DOMINANT FEATURE OVER
THE WESTERN ATLANTIC-CARIBBEAN BASIN THROUGH AT LEAST MONDAY
AFTERNOON...WITH AXIS TO THEN RAPIDLY CRUMBLE UNDER PRESSURE FROM
POLAR FRONT EXITING THE EASTERN USA. EARLY IN THE PERIOD THIS IS
TO FAVOR LOW LEVEL WINDS OF 25-30KT. THROUGH SUNDAY MORNING THE
WINDS DECREASE TO 15-20KT. LIGHTER WINDS WILL THEN ALLOW DIURNAL
HEAT CYCLE TO PREVAIL...WITH SEA BREEZE DRIVEN CONVECTION TO
CLUSTER ACROSS INTERIOR PORTIONS OF PUERTO RICO. PWAT CONTENT
DURING THE NEXT FEW DAYS IS TO PEAK AROUND 1.25 INCHES. THIS IS
ENOUGH TO FEED GENERATION OF TRADE WIND SHOWERS AND DIURNAL
CONVECTION ACROSS THE FORECAST AREA.

AS THE AIR MASS GROWS UNSETTLED...EXPECTING A GRADUAL INCREASE IN
CONVECTION ACROSS THE ENTIRE FORECAST AREA. OVERALL EXPECTING
MODERATE RAINFALL AMOUNTS...WITH LOCALLY HEAVY PROBABLE ACROSS EL
YUNQUE AND OVER SOUTHWEST PUERTO RICO IN AFTERNOON CONVECTION.
DOWNDRAFT GENERATED GUSTY WINDS...IF ANY...WILL GENERALLY LIMIT TO
THE DAY TODAY...WHEN MODELS SHOW VERTICAL SPEED SHEAR AND DRY AIR
ENTRAINMENT. RISK DECREASES DURING THE WEEKEND AS THE WINDS WANE
AND THE SHEAR ABATES.

DAVISON/GALVEZ...WPC (USA)