Prognostic Meteorological Discussion
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FXCA20 KWBC 171129
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
729 AM EDT WED SEP 17 2014

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. TUTT PATTERN
NORTH OF THE ISLANDS CONTINUE TO WEAKEN AS DEEP POLAR TROUGH
ESTABLISHES A FOOTHOLD ACROSS THE EASTERN USA/WESTERN ATLANTIC. AT
MID LEVELS...PER MODEL ANALYSIS...A SHORT WAVE RIDGE EXTENDS WEST
ACROSS THE NORTHEAST CARIBBEAN ISLANDS...SUSTAINING A WEAK MID
LEVEL CAP ACROSS THE FORECAST AREA. AT LOW LEVELS...A TROPICAL
WAVE LIES JUST EAST OF THE LESSER ANTILLES. THIS WAVE SUSTAINS AN
ITCZ CONNECTION...DRAWING MOISTURE NORTHWARD WHILE FAVORING PWAT
AMOUNTS OF TWO INCHES ALONG AND BEHIND THE WAVE AXIS. ANOTHER
FOLLOWS...WITH AXIS NORTH ALONG 36W/37W.

AT UPPER LEVELS...WANING TUTT PULLS ACROSS THE FORECAST AREA LATER
THIS AFTERNOON. AS IT SWINGS ACROSS PUERTO RICO AND THE VIRGIN
ISLES THE MODEL GUIDANCE SHOWS A DIVERGENT PATTERN ALOFT AHEAD OF
THIS AXIS. ALTHOUGH EXPECTING SOME POSITIVE INTERACTION BETWEEN
THIS FEATURE AND SEA BREEZE CONVERGENCE/DIURNAL
HEATING...PERSISTENT MID LEVEL RIDGE PATTERN WILL LIKELY LIMIT
FORMATION OF DEEP CONVECTION TO THE WESTERN INTERIOR PORTIONS OF
PUERTO RICO. IN THIS AREA THE NMM VERSION OF THE HRWRF SHOWS
MAXIMA OF 2-3 INCHES IN SCATTERED CONVECTION. HIGHLY LOCALIZED
RELEASE OF ENERGY MIGHT LEAD TO SOME SEVERE CONVECTION.

AT MID LEVELS...RIDGE LIFTS ACROSS THE FORECAST AREA TROUGH MIDDAY
ON THURSDAY. WEAKENING OF MID LEVEL RIDGE PATTERN WILL COINCIDE
WITH ARRIVAL OF TROPICAL WAVE IN THE LOW LEVEL EASTERLY TRADES.
THIS IS TO CROSS THE MONA PASSAGE EARLY ON FRIDAY MORNING...WITH
TRAILING MOIST PLUME TO REMAIN ACROSS THE VIRGIN ISLES-PUERTO RICO
THROUGH THE AFTERNOON HOURS. INITIALLY...THE MOST ACTIVE
CONVECTION IS EXPECTED ACROSS THE VIRGIN ISLES DURING THE LATE
AFTERNOON/EVENING HOURS...WHILE OVER PUERTO RICO IT IS TO THEN
SUSTAIN SCATTERED CONVECTION ACROSS EASTERN-SOUTHERN PORTIONS OF
THE ISLAND THROUGH EARLY MORNING HOURS ON FRIDAY. BUT THROUGH THE
DAY ON FRIDAY...AS MOIST PLUME PERSISTS ACROSS THE FORECAST
AREA...THE GFS AND UKMET SHOW CONVECTION BUILDING NORTH ACROSS
PUERTO RICO. IN A LONG FETCH SOUTHEASTERLY FLOW...MOST ACTIVE IS
EXPECTED IN THE AFTERNOON TO CLUSTER ACROSS WESTERN INTERIOR AND
NORTHWEST PORTIONS OF PUERTO RICO. ALTHOUGH MODELS SHOWING MAXIMA
OF LESS THAN AN INCH...STRONG FORCING WILL LIKELY RESULT IN MUCH
HIGHER AMOUNTS.

MODELS THEN FORECAST A MID LEVEL SHORT WAVE TROUGH TO ENTER THE
LESSER ANTILLES AROUND NOONTIME ON FRIDAY...CROSSING THE VIRGIN
ISLES TO EASTERN PUERTO RICO DURING THE EARLY AFTERNOON HOURS ON
SATURDAY. AT LOW LEVELS...THE NEXT TROPICAL WAVE IS TO ENTER THE
ISLAND CHAIN EARLY ON SUNDAY...AND ACROSS THE VIRGIN ISLES TO
PUERTO RICO LATER IN THE DAY. UNDER INFLUENCE OF SHORT WAVE TROUGH
ALOFT...CONDITIONS ARE TO REMAIN FAVORABLE AND CONDUCIVE TO
ORGANIZED DEEP CONVECTION.

VALVERDE...IMN (COSTA RICA)
MEDINA...ONAMET (REPUBLICA DOMINICANA)
DAVISON...WPC (USA)
$$




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