Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXCA20 KWBC 221200
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
800 AM EDT SUN OCT 22 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE VI FROM OCT 22/06
UTC: FAIR AND WINDY CONDITIONS ARE TO CONTINUE INTO MID-NEXT
WEEKS. TRADE WIND SHOWERS ARE FORECAST TO BE LIGHT...ISOLATED AND
VERY BRIEF...AS THEY WILL BE STREAMING FROM EAST TO WEST EMBEDDED
IN 15-20KT TRADES.

AT UPPER LEVELS...A DEEP UPPER TROUGH TO THE NORTHWEST OF THE
ISLANDS NOW CENTERS ON A LOW AT 26N 64W. THE TROUGH IS DEVELOPING
AN AXIS TO THE SOUTH INTO PUERTO RICO. ALTHOUGH THIS TROUGH IS
MEANDERING TO THE SOUTH EAST...ITS EXERTING LIMITED EFFECTS IN THE
ISLANDS WHILE A DRY AIR MASS LINGERS IN THE MID-TROPOSPHERE. AT
LOW LEVELS...A THE AXIS OF A TRADE WIND SURGE EXTENDS NOW TO THE
WEST OF JAMAICA. BEHIND THE SURGE...OVER PUERTO RICO AND THE
VI...A SUBSIDENCE CAP SITS AT 900 HPA AND VERY DRY AIR LIES OVER
THE INVERSION. TRADE ARE ALSO FAST...AS WIND SPEEDS RANGE BETWEEN
15 AND 20KT. THIS IS LEADING TO STREAMING LIGHT AND ISOLATED TRADE
WIND SHOWERS.

MODELS INDICATE THAT THE BASE OF THE UPPER TROUGH WILL MEANDER
FROM PUERTO RICO IN SUNDAY MORNING TO THE LEEWARD
ISLANDS-NORTHEASTERN VENEZUELA BY MONDAY EVENING. THIS WILL PLACE
PUERTO RICO AND THE VI UNDER THE UPPER CONVERGENT PATTERN OF THE
TROUGH...WHICH WILL CONTINUE SUSTAINING THE TRADE WIND CAP AND
LIMITING THUNDERSTORM DEVELOPMENT. POSITIVE INTERACTION BETWEEN
THE TROUGH AND THE MOISTURE PLUME IN THE SOUTHEASTERN CARIBBEAN IS
FORECAST TO LIMIT TO LATITUDES TO THE SOUTH OF 15N...AND TO
LONGITUDES TO THE EAST OF 65W. THIS WILL SUSTAIN A WET SPELL IN
THE FRENCH ISLES AND WINDWARD ISLANDS DURING
MONDAY-WEDNESDAY...WHILE PUERTO RICO AND THE VI CONTINUE
EXPERIENCING FAIR CONDITIONS. UNDER THE INFLUENCE OF THE UPPER LOW
TO THE NORTH...WINDS ARE TO DECREASE IN SPEED TO 10-15KT DURING
TUESDAY...AND BY LATE TUESDAY/EARLY WEDNESDAY THEY WILL SHIFT TO
SOUTHEASTERLIES. THIS WILL SHIFT THE AREAS OF AFTERNOON
PRECIPITATION TO NORTHEASTERN PUERTO RICO BY MID-WEEK.

IN THE MEAN TIME...ACTIVITY WILL BE CHARACTERIZED BY LIGHT...BRIEF
AND ISOLATED TRADE WIND SHOWERS MOSTLY AFFECTING THE VIRGIN
ISLANDS AND EASTERN PUERTO RICO. EXPECTING DAILY ACCUMULATIONS OF
0.2 INCHES...AND MAXIMA OF 0.5 INCHES IN AREAS OF OROGRAPHIC
UPLIFT. ALSO...AFTERNOON CONVECTION WILL CLUSTER IN EXTREME
WESTERN PUERTO RICO. UNDER THE PROXIMITY OF THE UPPER
TROUGH...EXPECTING ISOLATED THUNDERSTORMS TO DEVELOP. YET...THE
SHEAR WILL BE TOO LARGE...AND THE MID-LEVELS TOO DRY TO SUSTAIN
LONG LIVED HEAVY RAIN PRODUCING CELLS. THUS WE EXPECT ISOLATED
MAXIMA NEARING 1 INCH IN THE STRONGEST THUNDERSTORMS BETWEEN
MAYAGUEZ AND AGUADILLA ON A DAILY BASIS. AFTER TUESDAY...AFTERNOON
CONVECTION WILL CONCENTRATE IN THE VICINITY OF AGUADILLA AND OTHER
LOCATIONS IN NORTHWESTERN PUERTO RICO TO PRODUCE MAXIMA UNDER 1
INCH.

GUY...NMS (BELIZE)
PECK...MS (JAMAICA)
GALVEZ...WPC (USA)
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.