359
FXCA20 KWBC 211204
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
803 AM EDT FRI JUL 21 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUL
21/12UTC: A SAHARAN AIR LAYER CONTINUES EXTENDING ACROSS THE
ENTIRE NORTHERN CARIBBEAN AND EAST ACROSS THE TROPICAL ATLANTIC
INTO 50W ON FRIDAY MORNING. IN THE MID-LEVELS...A RIDGE CENTERED
OVER THE BAHAMAS AND EXTENDED AN AXIS ACROSS PUERTO RICO INTO THE
CENTRAL LESSER ANTILLES. THIS IS REINFORCING THE CURRENT DRY
PATTERN ASSOCIATED WITH THE SAL. IN FACT...THE TWIN ALGORITHM
SHOWS A STRONG LOW-LYING TRADE WIND CAP...WHICH IS CONFIRMED BY
THE SAN JUAN 00 UTC SOUNDING SHOWING THE INVERSION NEAR 850 HPA.
AVAILABLE MOISTURE IS WELL BELOW AVERAGE AND AROUND 1.4 INCHES.
SATELLITE IMAGERY SHOWS VERY LITTLE CLOUDINESS ACROSS PUERTO RICO
AND THE VI AND A STRONG SIGNATURE OF DUST...EVIDENT IN THE
GEOCOLOR PRODUCT.
THE MID-LEVEL RIDGE IS FORECAST TO WEAKEN THROUGH SUNDAY. THIS
COINCIDES WITH A DECREASE IN THE DENSITY OF THE SAHARAN AIR LAYER.
YET...NOTE THAT A THINER SAL IS EXPECTED TO PERSIST IN THE AREA AT
LEAST INTO TUESDAY. AS THE RIDGE WEAKENS...THE TRADE WIND CAP IS
FORECAST TO WEAKEN...ALLOWING FOR AN INCREASE IN VERTICAL MIXING
AND VERTICAL GROWTH OF DEVELOPING CONVECTION. LIMITING FACTORS FOR
SIGNIFICANT ACCUMULATIONS WILL BE BELOW AVERAGE LEVELS OF
AVAILABLE MOISTURE THROUGH MONDAY...AND ACCELERATED EASTERLY
TRADES...WHICH WILL FAVOR ENHANCED WIND SHEAR AND SHORT RESIDENCE
TIMES OF DEVELOPING CONVECTION. THROUGH THE WEEKEND...EXPECT VERY
ISOLATED PRECIPITATION FOCUSING IN EASTERN PUERTO RICO DUE TO
TRADE WIND CONVERGENCE...AND IN WESTERN PR IN AFTERNOON
SHORT-LIVED CONVECTION. EXPECT TRACE AMOUNTS ON
FRIDAY...INCREASING TO MAXIMA OF 0.2-0.3 INCHES IN WESTERN AND
NORTHWEST PUERTO RICO ON SATURDAY AND SUNDAY. IN EASTERN PR EXPECT
MAXIMA GENERALLY UNDER 0.15 INCHES.
WETTER CONDITIONS ARE FORECAST TO GRADUALLY DEVELOP STARTING ON
MONDAY...UNDER THE INFLUENCE OF A TROPICAL WAVE APPROACHING FROM
THE EAST...AND A TROPOSPHERIC KELVIN WAVE APPROACHING FROM THE
WEST. THE WAVE IS FORECAST TO CROSS PUERTO RICO SOMETIME BETWEEN
TUESDAY AND WEDNESDAY...BUT THERE IS STILL UNCERTAINTY ON THE
TIMING OF THE CROSSING AND ON THE MERIDIONAL EXTENSION OF
PRECIPITATING CONVECTION. OUR CURRENT FORECASTS REFLECTS AN
INCREASE IN PRECIPITATION ACROSS THE VI LATE ON MONDAY INTO
TUESDAY MORNING...TO FAVOR MAXIMA GENERALLY UNDER 0.25 INCHES. IN
EASTERN PR...EXPECT MAXIMA OF 0.2-0.4 INCHES FROM MONDAY THROUGH
TUESDAY MORNING. LARGER ACCUMULATIONS ARE EXPECTED ON
TUESDAY...WHEN AMOUNTS ARE LIKELY TO REACH THE 0.25-0.5 RANGE FOR
THE WESTERN VI AND EASTERN PUERTO RICO...WHILE AFTERNOON
CONVECTION IN THE WESTERN CORDILLERA PRODUCES MAXIMA OF 0.5-0.75
INCHES. TUESDAY'S FORECAST IS PRONE TO ADJUSTMENTS DUE TO
UNDERTAINTIES REGARDING THIS TROPICAL WAVE.
GALVEZ...WPC (USA)
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page