731
FXCA20 KWBC 021615
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1115 AM EST THU JAN 02 2025
WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI JAN 02 16 UTC:
THE LARGE SCALE ANALYSIS SHOWS A DISORGANIZED UPPER DIVERGENT
PHASE OF THE MJO CENTERING OVER THE TROPICAL ATLANTIC AND ENTERING
AFRICA. THE REAR END OF THIS PHASE IS STILL OVER THE
CARIBBEAN...BUT IT IS EXPECTED TO HAVE LIMITED IMPACTS IN THE
NORTHEAST CARIBBEAN GIVEN THE PRESENCE OF A MID-LEVEL RIDGE AND
ASSOCIATED STABLE LAYER. GIVEN THE CURRENT PROPAGATION OF THE
MJO...WE EXPECT CONDITIONS TO BECOME UPPER CONVERGENT BY THE
SECOND WEEK OF JANUARY. THESE GENERALLY ASSOCIATE WITH DRIER
CONDITIONS...BUT ALSO WITH ENHANCED TRADE WIND SPEEDS. ALTHOUGH
THE LATTER ASSOCIATED WITH HIGHER VALUES OF VERTICAL WIND SHEAR
AND GENERALLY LESSER ACCUMULATIONS...THEY COULD ALSO YIELD TO
LOCAL ENHANCEMENT OF OROGRAPHICALLY-INDUCED MAXIMA AND LIGHT
NOCTURNAL/EARLY MORNING SHOWERS. BUT THIS WILL DEPEND ON THE
SYNOPTIC VARIABILITY OF THE TRADES WHEN THE MJO BECOMES UPPER
CONVERGENT.
THE ANALYSIS OF CURRENT CONDITIONS SHOWS THE PRESENCE OF A MID
LEVEL RIDGE PATTERN ACROSS THE TROPICAL ATLANTIC AND EASTERN
CARIBBEAN. TWO CENTERS OF CIRCULATION ARE PRESENT IN THIS
RIDGE...ONE NEAR 23N 60W AND ANOTHER JUST TO THE SOUTH OF
HISPANIOLA. THIS ASSOCIATES WITH A TRADE WIND CAP. THE SAN JUAN 12
UTC SOUNDING SHOWS A CAP LOCATED NEAR 800 HPA AND A STRONGER CAP
LOCATED NEAR 700 HPA...WHICH IS CONSISTENT EITH THE SATELLITE
PRESENTATION OF STRATIFORM STRUCTURES EMBEDDED IN SHALLOW TRADE
WIND CONVECTION. ON THRUSDAY MORNING...ACTIVITY IS ORGANIZING IN
WEAK TROUGHS PROPAGATING WESTWARD IN THE EASTERLY TRADES. ONE IS
CROSSING THE VIRGIN ISLANDS THIS MORNING...AND RADAR DATA CONFIRMS
THAT PRECIPITATION IS ISOLATED AND VERY LIGHT WITH THIS
PERTURBATION. OF INTEREST FOR LATER IN THE FORECAST CYCLE...A
FRONT EXTENDS FROM THE FAR NORTHERN ATLANTIC ACROSS THE NORTHWEST
BAHAMAS AND INTO NORTH CUBA. THIS FEATURE IS FORECAST TO
ACCELERATE SOUTHEASTWARD DURING THE WEEKEND FAVORING A PEAK IN
PRECIPITATION IN PUERTO RICO ON DURING SUNDAY/MONDAY DUE TO DIRECT
IMPACTS.
REGARDING THE FORECAST...EXPECT THE NORTHEAST CARIBBEAN TO REMAIN
UNDER THE INFLUENCE OF THE SUBTROPICAL UPPER RIDGE AND A MID-LEVEL
RIDGE THROUGH THE FORECAST CYCLE. THE MID-LEVEL RIDGE WILL
GENERALLY LIMIT THE VERTICAL DEVELOPMENT OF CONVECTION LIMITING
POTENTIAL PRECIPITATION AMOUNTS. EXPECT A DECREASE IN STABILITY ON
SATURDAY AND SUNDAY DUE TO THE INFLUENCE OF THE BASE OF A
MID-LEVEL TROUGH ARRIVING IN THE WESTERLIES...JUST NORTH OF THE
MID-LEVEL RIDGE AXIS. THIS TROUGH WILL LIKELY ENTER IN PHASE WITH
THE SURFACE FRONT AND PREFRONTAL FEATURES...AS WELL AS WITH THE
RAPID ACCELERATION OF NORTHEASTERLY LOW-LEVEL WINDS ON SATURDAY
AFTERNOON. THIS WILL FAVOR A RAPID INCREASE IN PRECIPITABLE WATER
AND LOW-LEVEL MOISTURE CONVERGENCE...RESULTING ON A NOTICEABLE
INCREASE IN SHOWERS AND ASSOCIATED AMOUNTS ON SATURDAY
AFTERNOON/EVENING. MODELS DO AGREE ON A RAPID INCREASE IN
PRECIPITABLE WATER DURING THE DAY ON SATURDAY...YIELDING TO VALUES
EXCEEDING 45MM IN NORTHEAST PUERTO RICO AND THE NORTHERN VI BY
SATURDAY EVENING. THIS MEANS MOISTURE AVAILABILITY WELL ABOVE
NORMAL FOR EARLY JANUARY...LASTING FROM MIDDAY SATURDAY LASTING
THROUGH AT LEAST SUNDAY EVENING. CONFIDENCE FOR WET CONDITIONS ON
SATURDAY INTO SUNDAY MORNING/MIDDAY IS HIGH...YET THE CONFIDENCE
DECREASES RAPIDLY PAST MIDDAY SUNDAY IN ASSOCIATION WITH MODELS
STRUGGLING TO RESOLVE THA RATE OF DRYING ONCE THE WET SPELL WANES.
THE GFS IS TRENDING WETTER THAN THE ECMWF AND OTHER
GUIDANCE...FAVORING A LONGER PERIOD WITH ENHANCED SHOWERS EMBEDDED
IN THE EAST-NORTHEASTERLY TRADES...SHOWING INTERMITTENT SHOWERS
INTO MONDAY. GIVEN GUIDANCE CONSENSUS AND THE BUILDING OF THE
MID-LEVEL RIDGE DURING SUNDAY INTO EARLY NEXT WEEK...WE ARE
LEANING TOWARDS THE DRIER SOLUTIONS...SUGGESTING A PEAK IN
PRECIPITATION ON SATURDAY EVENING THROUGH SUNDAY MORNING...AND A
GRADUAL DECREASE IN THE INTENSITY AND FREQUENCY OF TRADE WIND
SHOWERS DURING SUNDAY THROUGH MIDDAY MONDAY. IN TERMS OF
ACCUMULATIONS...THERE IS GUIDANCE AGREEMENT ON SATURDAY THROUGH
SUNDAY MORNING...WHEN WE EXPECT SCATTERED AMOUNTS OF 0.4-0.8
INCHES ALONG THE ENTIRE NORTH AND NORTHEAST COAST TIER OF PUERTO
RICO AND ISOLATED MAXIMA NEARING 1 INCH. ON SUNDAY...THE VEERING
OF THE LOW-LEVEL WINDS FROM NORTHEASTERLIES TO
EAST-NORTHEASTERLIES WILL FAVOR THE LARGEST ACCUMULATIONS IN
EASTERN...NORTHEASTERN AND NORTH-CENTRAL PUERTO RICO. IN THESE
LOCATIONS WE SEE THE POTENTIAL FOR AMOUNTS IN THE 0.2-0.4 INCH
RANGE...AND POTENTIAL ISOLATED MAXIMA NEARING 0.75 INCHES IN
NORTHEAST PUERTO RICO AND PORTIONS OF EL YUNQUE-LUQUILLO.
GALVEZ...WPC(USA)
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