Prognostic Meteorological Discussion
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FXCA20 KWBC 211101
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
700 AM EDT SAT OCT 21 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE VI FROM OCT 21/06
UTC: FAIR AND WINDY CONDITIONS ARE TO PREVAIL DURING THE NEXT
SEVERAL DAYS. A DEEP AND ELONGATED UPPER TROUGH HAS EXISTED THE
UNITED STATES EAST COAST AND NOW EXTENDS AN AXIS ALONG 33N 60W
INTO THE SOUTHEASTERN BAHAMAS AT 24N 73W. THE UPPER TROUGH IS
PROPAGATING TO THE SOUTH WEST TOWARDS THE ISLANDS. THIS TROUGH IS
PRESSING INTO AN UPPER RIDGE THAT EXTENDS AN AXIS FROM THE
NORTHERN ANTILLES TO THE NORTHEAST ALONG 20N 60W...AND INTO 32N
43W. AT LOW-LEVELS...A TRADE WIND SURGE HAS CROSSED THE EASTERN
AND CENTRAL CARIBBEAN FROM EAST TO WEST AND NOW EXTENDS AN AXIS
ACROSS WESTERN HAITI/TURKS AND CAICOS. THE AIR MASS BEHIND THE
SURGE...NOW SITTING OVER PUERTO RICO AND THE VI...IS CHARACTERIZED
BY A TRADE WIND CAP NEAR 900 HPA...AND BY A VERY DRY TROPOSPHERE
OVER THE INVERSION. WINDS ARE FROM THE EAST AT 15-20KT. THIS IS
SUSTAINING ISOLATED...LIGHT AND RAPIDLY-MOVING TRADE WIND SHOWERS.
DEEP-LAYER MOISTURE LIES FAR SOUTH ALONG THE EXTREME SOUTHERN
CARIBBEAN...WHERE IT IS FORECAST TO REMAIN THROUGH THE NEXT
SEVERAL DAYS.

MODELS SHOW THE UPPER TROUGH NEAR THE BAHAMAS PROPAGATING
SOUTHEASTWARD. THE BASE OF THE UPPER TROUGH IS FORECAST TO REACH
PUERTO RICO BY SUNDAY MORNING. YET...THE MID-TROPOSPHERE WILL
CONTINUE BEING TOO DRY TO SUSTAIN HEAVY RAINFALL...AND MODELS ARE
AGREEING IN THUNDERSTORMS DEVELOPMENT CONSTRAINING TO REGIONS TO
THE NORTH OF 21-22N. THE TROUGH IS THEN FORECAST TO SLOW DOWN ITS
PROPAGATION...AND BY MONDAY EVENING IT IS FORECAST TO EXTEND AN
AXIS ACROSS THE LEEWARD ISLANDS INTO NORTHEASTERN VENEZUELA. 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 THE EAST OF 65W. THIS WILL SUSTAIN A WET
SPELL IN THE FRENCH ISLES AND LESSER ANTILLES DURING
MONDAY-WEDNESDAY...WHILE PUERTO RICO AND THE VI CONTINUE
EXPERIENCING FAIR CONDITIONS.

IN TERMS OF THE PRECIPITATION PATTERNS AND
ACCUMULATIONS...EXPECTING ISOLATED BUT NUMEROUS LIGHT TRADE WIND
SHOWERS DOTTING THE VIRGIN ISLANDS AND EASTERN PUERTO RICO
ESPECIALLY DURING LATE NIGHT AND EARLY MORNING HOURS. THIS WILL
LEAD TO DAILY ACCUMULATIONS IN THE ORDER OF 0.2 INCHES/DAY...AND
0.5 INCHES/DAY IN REGIONS OF ENHANCED OROGRAPHIC UPLIFT IN EASTERN
SLOPES OF EASTERN PUERTO RICO. DURING THE AFTERNOON...SHOWERS ARE
TO CONCENTRATE IN WESTERN PUERTO RICO. THERE IS A CHANGE FOR
ISOLATED THUNDERSTORMS ON SUNDAY AND MONDAY IN THE WESTERN
CORDILLERA...YET ANY DEEP CONVECTION WILL BE SHORT LIVED AND MOVE
RAPIDLY WESTWARD...WHICH WILL LIMIT MAXIMUM ACCUMULATIONS ALSO TO
0.3-0.5 INCHES.

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




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