879
FXCA20 KWBC 111228
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
727 AM EST MON DEC 11 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI DEC 11/12UTC:
IN THE MID-LEVELS...A RIDGE CENTERS NEAR 27N 69W AND EXTENDS OVER
MOST OF THE NORTHEAST CARIBBEAN ON MONDAY MORNING. THIS ASSOCIATES
WITH A TRADE WIND CAP. HOWEVER...THE CAP IS ELEVATED AND SITS NEAR
700 HPA OVER PUERTO RICO AS EVIDENCED BY THE 00 UTC SAN JUAN
SOUNDING. THIS IS ALLOWING FOR SOME VERTICAL DEVELOPMENT IN
SHALLOW CONVECTIVE CELLS PROPAGATING IN THE EASTERLY TRADES. IN
THE LOW LEVELS...A POTENT RIDGE THAT CENTERS NEAR 40N 52W HAS
TIGHTENED THE PRESSURE GRADIENT OVER THE NORTHEAST CARIBBEAN. THIS
HAS RESULTED IN AN ACCELERATION OF THE TRADES TO SPEED OF 20-25KT
BETWEEN 950 AND 700 HPA. THIS IS FAVORING POCKETS OF LIGHT TRADE
WIND SHOWERS MOSTLY EAST OF THE VIRGIN ISLANDS...ANTHOUGH THE SAN
JUAN RADAR SHOWS VERY ISOLATED SHOWERS IN PORTIONS OF EASTERN
PUERTO RICO AS WELL.
MODELS SHOW THE CURRENT MID-LEVEL RIDGE WEAKENING THROUGH LATE
TUESDAY...WHILE A STRONGER RIDGE ARRIVES FRON THE NORTH AND
STRENGTHENS ON WEDNESDAY THROUGH THURSDAY WHILE CENTERING NEAR
22-25N AND 65-67W. THIS RIDGE WILL LIKELY LOWER THE TRADE WIND CAP
AND STRENGTHEN IT...LEADING TO A DECREASE IN AFTERNOON CONVECTION
IN WESTERN PUERTO RICO ON WEDNESDAY AND THURSDAY WHILE ENHANCING
CLOUD COVER AND LOW-LEVEL MOISTURE IN NORTHERN PUERTO RICO. IN THE
LOW-LEVELS...THE TRADES ARE FORECAST TO BACK AND ACQUIRE AN
EAST-NORTHEASTERLY DIRECTION ON TUESDAY WHILE ACCELERATING TO
SPEEDS OF 30-35KT. THE STRONG WINDS ARE LIKELY TO PERSIST THROUGH
WEDNESDAY AFTERNOON/EVENING...LIKELY FAVORING 10M WIND SPEEDS
APPROACHING OR EVEN EXCEEDING 20KT DURING PERIODS. THE STRONG
NORTHEASTERLY TRADES WILL LIKELY ENHANCE THE EXTRACTION OF
MOISTURE FROM THE OCEAN AS WELL AS SHALLOW CONVECTIVE INSTABILITY
OVER WATERS...FAVORING AN INCREASE IN THE COVERAGE AND FREQUENCY
OF LIGHT TRADE WIND SHOWERS ESPECIALLY IN LATE EVENING THROUGH
EARLY MORNING HOURS. THIS WILL FAVOR PERSISTENT WET CONDITIONS IN
NORTHERN AND EASTERN PUERTO RICO ON A DAILY BASIS...FAVORING
FIVE-DAY TOTALS OF 1-1.75 INCHES FROM NORTH-CENTRAL TO NORTHEAST
AND EASTERN PUERTO RICO.
ON MONDAY...EXPECT THE LARGEST AMOUNTS IN EAST AND NORTHEAST
PUERTO RICO WHERE SCATTERED SHOWERS WILL FAVOR MAXIMA OF 0.15-0.3
INCHES...WHILE AFTERNOON CONVECTION IN THE FAR WEST CORDILLERA
FAVORS MAXIMA UNDER 0.2 INCHES. ON TUESDAY...THE INCREASE IN THE
NORTHERLY COMPONENT OF THE LOW-LEVEL WINDS WILL FAVOR A SLIGHT
INCREASE IN THE COVERAGE OF PRECIPITATING CONVECTION AND MAXIMA IN
NORTHERN PUERTO RICO...AS WELL AS A SHIFT IN THE LOCATION OF
AFTERNOON MAXIMA TO FAR SOUTHWEST PUERTO RICO...STILL FAVORING
MAXIMA UNDER 0.2 INCHES. ON WEDNESDAY AND THURSDAY...EXPECT A
DECREASE IN AFTERNOON CONVECTION AS THE TRADE WIND CAP
STRENGTHENS. YET...CONTINUED MOISTURE CONVERGENCE ALONG NORTHERN
AND EASTERN PUERTO RICO UNDER THE ACCELERATED NORTHEASTERLY TRADES
WILL SUSTAIN SCATTERED MAXIMA OF 0.2-0.35 INCHES. ON FRIDAY...THE
TRADE WIND CAP IS EXPECTED TO WEAKEN WHILE THE TRADES SHIFT TO
EASTERLIES. THIS WILL RELOCATE THE LARGEST ACCUMULATIONS TO
EASTERN PUERTO RICO WHERE EXPECT MAXIMA OF 0.3-0.5 INCHES.
GALVEZ...WPC (USA)
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