733
FXCA20 KWBC 201243
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
743 AM EST WED DEC 20 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI DEC 20/12UTC:
UNDER THE INFLUENCE OF AN AMPLIFIED TRAIN OF UPPER RIDGES AND
TROUGHS IN THE WESTERLIES...SEVERAL BOUNDARIES ARE PRESENT IN THE
CARIBBEAN AT THE LOW LEVELS. A STATIONARY FRONT EXTENDS
MERIDIONALLY ALONG 26N 66W INTO HISPANIOLA AND THEN INTO FAR WEST
PANAMA...WHILE A FRONTAL SJHEAR LINE EXTENDS INTO THE WINDWARD
ISLANDS. PUERTO RICO AND THE VI...WEAK NORTHERLY TRADES ARE
PRESENT. THE SAN JUAN OO UTC SOUNDING SHOWS AN INVERSION SITTING
AT 850 HPA. PRECIPITABLE WATER REMAINS JUST BELOW 40MM THIS
MORNING...BUT A POCKET OF MOISTURE WITH VALUES OF 40-45MM IS
APPROACHING THE ISLANDS FROM THE NORTH. THIS ASSOCIATED WITH
SCATTERED SHALLOW CONVECTION. AS THIS MOIST POOL CROSSES THE
ISLANDS DURING THE DAY ON WEDNESDAY...IT WILL FAVOR LIGHT TRADE
WIND SHOWERS PRIMARILY IN NORTHEAST AND EASTERN PUERTO
RICO/WESTERN VI INITIALLY...AND IN SOUTHEAST AND SOUTH CENTRAL
PUERTO RICO IN THE AFTERNOON.
WESTERLIES HAVE ESTABLISHED IN THE MID-TROPOSPHERE DOWN TO 600
HPA. EMBEDDED IN THESE WESTERLIES...PERTURBATIONS ARE MOVING IN
FROM THE WEST. THE PERSISTENT MID-LEVEL TROUGH PATTERN AND
EMBEDDED PERTURBATIONS ARE EXPECTED TO ERODE THE TRADE WIND CAP
FAVORING AN INCREASE IN VERTICAL DEVELOPMENT OF CONVECTION INTO
THE WEEKEND. A FRONT APPROACHES FROM THE NORTH ON THURSDAY AND
FRIDAY. THE INCREASING WIND SPEEDS OF THE NORTHEASTERLY TRADES
WILL STIMULATE CONVECTIVE INSTABILITY AND AVAILABLE
MOISTURE...YIELDING TO AN INCREASE IN PRECIPITATION FROM THURSDAY
EVENING THROUGH SATURDAY. THE LARGEST ACCUMULATIONS ARE EXPECTED
IN NORTHERN AND NORTHEAST PUERTO RICO WHERE EXPECT MAXIMA OF
0.3-0.5 INCHES ON A DAILY BASIS. THIS DECREASES ON SUNDAY AS THE
AXIS OF A BROAD MID-UPPER TROUGH MOVES EAST OF THE ISLANDS
ENHANCING UPPER CONVERGENCE AND FAVORING A DECREASE IN
ACCUMULATION. NOTE THAT UNDER FAVORABLE MADDEN-JULIAN OSCILLATION
CONDITIONS FOR HEAVIER PERCIPITATION...LOCALIZED MAXIMA COULD
EXCEED THE FORECAST AMOUNTS REPRESENTED IN THE QPF CHARTS.
GALVEZ...WPC (USA)
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