578
FXCA62 TJSJ 270903
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
503 AM AST FRI JUN 27 2025
KEY MESSAGES
* A TRADE WIND PERTURBATION WILL INCREASE THE ACTIVITY OF SHOWERS
TODAY, WITH A BETTER CHANCE FOR AFTERNOON THUNDERSTORMS.
* A TROPICAL WAVE WILL APPROACH PUERTO RICO AND THE U.S. VIRGIN
ISLANDS FROM THE EASTERN CARIBBEAN LATE SATURDAY, CROSSING THE
ISLANDS ON SUNDAY.
* AN AREA WITH SLIGHTLY DRIER AIR AND SUSPENDED SAHARAN DUST
PARTICLES WILL ARRIVE EARLY NEXT WEEK.
* WINDS AND CHOPPY SEAS WILL CONTINUE TO PROMOTE LIFE-
THREATENING RIP CURRENTS ACROSS EXPOSED BEACHES.
SHORT TERM...TODAY THROUGH SUNDAY
TRANQUIL WEATHER CONDITIONS PERSISTED OVERNIGHT ACROSS PUERTO RICO
AND THE U.S. VIRGIN ISLANDS, CONSISTENT WITH PREVIOUS NIGHTS. A FEW
BRIEF, LIGHT SHOWERS MOVED ACROSS NORTHEASTERN PUERTO RICO,
PRODUCING MINIMAL RAINFALL ACCUMULATIONS. WINDS WERE GENERALLY FROM
THE EAST-NORTHEAST AT 5 TO 15 MPH, WITH STRONGER GUSTS NEAR THE
COAST. TEMPERATURES RANGED FROM THE UPPER 70S TO LOW 80S IN URBAN
AREAS AND FROM THE 60S TO LOW 70S IN MOUNTAINOUS REGIONS.
A GRADUAL INCREASE IN LOW-LEVEL MOISTURE AND PRECIPITABLE WATER
VALUES, RANGING BETWEEN 1.40 AND 1.80 INCHES, IS EXPECTED ACROSS THE
REGION TODAY THROUGH SATURDAY. FORECAST GUIDANCE CONTINUES TO
INDICATE THE APPROACH OF AN UPPER-LEVEL TROUGH, WHICH WILL ENHANCE
ATMOSPHERIC INSTABILITY, PARTICULARLY DURING THE AFTERNOON HOURS, AS
IT INTERACTS WITH LOCAL EFFECTS AND DIURNAL HEATING. THESE
CONDITIONS WILL FAVOR THE DEVELOPMENT OF SCATTERED TO NUMEROUS
SHOWERS AND ISOLATED THUNDERSTORMS, MAINLY OVER THE INTERIOR AND
WESTERN SECTIONS OF PUERTO RICO, AS WELL AS DOWNWIND FROM THE U.S.
VIRGIN ISLANDS.
ON SUNDAY, A SURGE OF TROPICAL MOISTURE ASSOCIATED WITH AN
APPROACHING TROPICAL WAVE IS ANTICIPATED. AT THIS TIME, SUNDAY IS
EXPECTED TO BE THE MOST ACTIVE AND UNSTABLE DAY OF THE SHORT-TERM
PERIOD, WITH PRECIPITABLE WATER VALUES ABOVE 2 INCHES. THE HIGHEST
RISK FOR FLOODING RAINS WILL BE FROM THE AFTERNOON INTO THE EVENING
HOURS, PARTICULARLY ACROSS AREAS WITH POOR DRAINAGE OR NEAR STEEP
TERRAIN. RESIDENTS AND VISITORS ARE ADVISED TO MONITOR THE FORECAST
IN THE COMING DAYS.
LONG TERM...MONDAY THROUGH FRIDAY
A MID-LEVEL RIDGE WILL BUILD AND HOLD OVER THE NORTHEAST
CARIBBEAN BY EARLY NEXT WEEK, ESTABLISHING A STRONG TRADE WIND
INVERSION THAT WILL PROMOTE SUBSIDENCE AND A DRIER ATMOSPHERE
ALOFT, SIGNIFICANTLY LIMITING DEEP CONVECTIVE DEVELOPMENT THROUGH
MIDWEEK. AT THE SAME TIME, A SAHARAN AIR LAYER (SAL) ARRIVED
BEHIND SUNDAY'S TROPICAL WAVE, RESULTING IN HAZY SKIES, DEGRADED
AIR QUALITY, AND REDUCED VISIBILITY FROM MONDAY THROUGH AT LEAST
TUESDAY. ONCE AGAIN, MODEL GUIDANCE INDICATES A TROPICAL WAVE
MOVING WELL SOUTH ACROSS THE SOUTHERN SECTION OF THE CARIBBEAN,
LEAVING THE ISLANDS UNDER THE INFLUENCE OF POCKETS OF MOISTURE
EMBEDDED WITHIN EASTERLY TRADE WINDS.
THE RIDGE ALOFT WILL WEAKEN AROUND WEDNESDAY AS THE DRY AIR MASS
LEAVES THE REGION, AND A RETROGRADING MID- TO UPPER-LEVEL
TROUGH/LOW MOVES CLOSER TO THE ISLANDS, INDUCING PERTURBATIONS AT
THE SURFACE. AS THE TROUGH RETROGRADES TOWARD THE NORTHEAST
CARIBBEAN, IT WILL INDUCE PERTURBATIONS IN THE SURFACE THAT WILL
BE PUSHED BY THE TRADES AT TIMES. HOWEVER, A TROPICAL WAVE IS
EXPECTED TO ARRIVE, INCREASING THE MOISTURE CONTENT BY LATE
THURSDAY NIGHT OR FRIDAY AND TRANSITIONING INTO A MORE UNSTABLE
WEATHER PATTERN.
TEMPERATURES ARE EXPECTED TO TREND ABOVE NORMAL, ESPECIALLY UNDER
THE INFLUENCE OF THE SAL, WHICH WILL REDUCE OVERNIGHT COOLING AND
RESULT IN WARMER MINIMUM AND MAXIMUM TEMPERATURES ACROSS THE
ISLANDS.
AVIATION
(06Z TAFS)
VFR CONDITIONS ACROSS ALL TAF SITES. HOWEVER, BRIEF MVFR CONDITIONS
ARE POSSIBLE NEAR TJBQ AND TJPS AFTER 27/17Z DUE TO VCTS POSSIBLE.
EXPECT E-NE WINDS RANGING FROM 8 TO 29 KT WITH OCCASIONAL HIGHER
GUSTS AFTER 27/13Z AND THROUGH 27/23Z.
MARINE
MARINERS CAN EXPECT CHOPPY SEAS ACROSS THE LOCAL ATLANTIC AND
CARIBBEAN WATERS DUE TO THE SURFACE HIGH PRESSURE ACROSS THE
ATLANTIC, SUPPORTING A MODERATE TO FRESH EASTERLY WIND FLOW. A TRADE
WIND PERTURBATION WILL ARRIVE TODAY, INCREASING THE POTENTIAL FOR
SHOWERS AND THUNDERSTORMS, FOLLOWED BY A TROPICAL WAVE LATE SATURDAY
NIGHT INTO SUNDAY.
BEACH FORECAST
WIND-DRIVEN SEAS WILL MAINTAIN A MODERATE RISK OF RIP CURRENTS
ALONG MOST EXPOSED BEACHES OF THE ISLANDS TODAY AND THROUGH MUCH
OF THE FORECAST PERIOD.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM...MMC
LONG TERM....CAM
AVIATION...MMC
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