039
FXCA62 TJSJ 150828
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
428 AM AST TUE APR 15 2025
SYNOPSIS
WE ANTICIPATE SHOWERS AND THUNDERSTORMS TO DEVELOP THIS AFTERNOON
ACROSS WEST TO NORTHWESTERN PR, ENHANCING THE RISK FOR URBAN AND
SMALL STREAM FLOODING, AS WELL AS MUDSLIDES AND RAPID RIVER RISES.
THE REMNANTS OF THIS ACTIVITY WILL LIKELY LINGER THROUGH THE
EVENING HOURS. OTHER HAZARD RISKS INCLUDE LIGHTNING OVER THE NEXT
FEW DAYS, WITH NON- THUNDERSTORM WIND RISKS ANTICIPATED TODAY. THE
RISK OF LIFE- THREATENING RIP CURRENTS WILL BE MODERATE TODAY FOR
MOST NORTH- AND EAST- FACING BEACHES. INCREASING WINDS AND A
NORTHERLY SWELL WILL LIKELY DETERIORATE MARINE AND SURF ZONE
CONDITIONS OVER THE WEEKEND.
SHORT TERM...TODAY TROUGH THURSDAY
TRANQUIL WEATHER CONDITIONS PREVAILED ACROSS THE ISLANDS DURING THE
NIGHT AND EARLY MORNING HOURS. RADAR DOPPLER SHOWED A FEW SHOWERS
MOVING INLAND, BUT NO SIGNIFICANT RAINFALL ACCUMULATIONS WERE
OBSERVED OR EVEN EXPECTED WITH THIS ACTIVITY. CLOUDINESS WAS PRESENT
FOR MOST OF THE NORTHEASTERN SECTION OF THE ISLAND AND THE U.S.
VIRGIN ISLANDS. OVERNIGHT TEMPERATURES WERE IN THE LOW 80S ACROSS
COASTAL REGIONS AND MUCH COLDER IN THE MOUNTAIN SECTIONS.
FROM TODAY THROUGH THURSDAY, PUERTO RICO AND THE U.S. VIRGIN ISLANDS
WILL REMAIN UNDER A MOIST AND SOMEWHAT UNSTABLE WEATHER REGIME. THE
GLOBAL MODEL INDICATES THAT PRECIPITABLE WATER (PWAT) VALUES WILL
STAY AT OR ABOVE 1.5 INCHES, REMAINING ABOVE THE CLIMATOLOGICAL
MEDIAN AND SUPPORTING CONDITIONS FOR FREQUENT PASSING SHOWERS AND
AFTERNOON CONVECTIVE ACTIVITY. MID- AND LOW-LEVEL RELATIVE HUMIDITY
VALUES, PARTICULARLY IN THE 700–500 MB AND 850–700 MB LAYERS, WILL
REMAIN NEAR OR ABOVE THE 50TH PERCENTILE, INDICATING A SUFFICIENTLY
MOIST COLUMN FOR SUSTAINED SHOWER DEVELOPMENT. WINDS WILL GRADUALLY
VEER FROM EASTERLY TODAY TO EAST-SOUTHEASTERLY BY WEDNESDAY, HELPING
TO TRANSPORT FRAGMENTED MOISTURE INTO THE REGION. THIS PATTERN
FAVORS PASSING SHOWERS OVER WINDWARD COASTAL AREAS DURING THE
MORNING HOURS, FOLLOWED BY ISOLATED THUNDERSTORMS ACROSS INTERIOR
AND WESTERN PUERTO RICO IN THE AFTERNOON.
BY WEDNESDAY, THE FOCUS OF CONVECTION WILL SHIFT TOWARD NORTHWESTERN
PUERTO RICO DUE TO THE EVOLVING SOUTHEASTERLY FLOW AND THE
DEVELOPMENT OF A SURFACE TROUGH WEST OF THE REGION. INSTABILITY
INCREASES AS AN UPPER LEVEL TROUGH MOVES MORE EASTWARD INTO THE
CARIBBEAN, LEAVING THE FORECAST AREA UNDER AN UNSTABLE PATTERN.
WIDESPREAD SHOWER ACTIVITY IS NOT ANTICIPATED DUE TO THE LACK OF
MOISTURE AT THE LOW LEVELS, THEREFORE, LOCALIZED SHOWERS ACROSS THE
WESTERN INTERIOR AND THE NORTHWESTERN SECTION OF THE ISLAND IS
EXPECTED EACH AFTERNOON. A WARMING TREND IS EXPECTED AT LOW LEVELS,
WITH 925 MB TEMPERATURES FORECAST TO REMAIN ABOVE THE 75TH
PERCENTILE. THIS, COMBINED WITH LINGERING MOISTURE, WILL INCREASE
THE HEAT RISK ACROSS MOST OF THE COASTAL AND URBAN AREAS, ESPECIALLY
FROM 10 AM TO 4 PM ON WEDNESDAY AND THURSDAY.
LONG TERM...FRIDAY THROUGH TUESDAY
UNSETTLED WEATHER CONDITIONS WILL DOMINATE THE FORECAST AREA AS LOW
PRESSURE OVER THE NORTH-NORTHWESTERN ATLANTIC CONTINUES TO DRAW
MOISTURE FROM THE CARIBBEAN. TOWARD THE END OF THE WORKWEEK AND INTO
THE WEEKEND, WINDS ARE EXPECTED TO SHIFT GRADUALLY FROM THE EAST-
SOUTHEAST TO THE NORTHEAST.
THE LATEST MODEL GUIDANCE CONTINUES TO INDICATE THE APPROACH OF A
TROUGH ACCOMPANIED BY A COLD FRONT, WHICH IS EXPECTED TO MOVE INTO
THE REGION ON SATURDAY. THESE FEATURES WILL ENHANCE THE POTENTIAL
FOR SHOWER AND THUNDERSTORM DEVELOPMENT, PARTICULARLY ACROSS THE
INTERIOR AND SOUTHWESTERN PORTIONS OF PUERTO RICO DURING THE
AFTERNOON AND EARLY EVENING HOURS. MODEL DATA SUGGESTS PRECIPITABLE
WATER VALUES RANGING FROM 1.8 TO 1.9 INCHES, 500 MB TEMPERATURES
BETWEEN -8 AND -9 DEGREES CELSIUS, AND DEEP-LAYER MOISTURE EXTENDING
FROM THE SURFACE UP TO AROUND 500 MB. THESE CONDITIONS WILL SUPPORT
THE POTENTIAL FOR URBAN AND SMALL STREAM FLOODING, RAPID RIVER
RISES, MUDSLIDES, AND FREQUENT LIGHTNING ASSOCIATED WITH
THUNDERSTORM ACTIVITY. AT THIS TIME, SATURDAY IS THE WETTEST DAY OF
THE LONG-TERM PERIOD.
A GRADUAL IMPROVEMENT IN WEATHER CONDITIONS IS ANTICIPATED FROM
SUNDAY THROUGH TUESDAY AS A DRIER AND COOLER AIR MASS IS FORECAST TO
MOVE INTO THE REGION BEHIND THE FRONT. THIS TRANSITION WILL BRING
LOWER HUMIDITY AND REDUCED RAIN CHANCES, SIGNALING A RETURN TO MORE
STABLE AND SEASONABLE CONDITIONS. LATE SATURDAY WINDS WILL INCREASE
AND BECOME BREEZY THROUGH AT LEAST TUESDAY.
AVIATION
(06Z TAFS)
MOSTLY, VFR CONDITIONS WILL PERSIST FOR ALL THE TAF SITES WITH SOME
BRIEF MVFR CONDITIONS ALONG THE TJBQ, TJPS, AND TJSJ AT AROUND
15/18Z WITH THE AFTERNOON CONVECTION (TSRA AND SHRA). THEREFORE, A
LOWER CEILING AND REDUCTION IN VIS ARE FORECASTED. WINDS WILL PEAK
AT 15/14Z FROM THE E-ESE UP TO 15 KNOTS, WITH GUSTY WINDS NEAR THE
STRONGEST SHOWERS.
MARINE
A HIGH PRESSURE SYSTEM BUILDING OVER THE WESTERN ATLANTIC WILL
PROMOTE MODERATE TO LOCALLY FRESH EAST TO NORTHEAST WINDS, GRADUALLY
VEERING TO BECOME EASTERLY TOMORROW AND EAST-SOUTHEASTERLY ON
WEDNESDAY. THIS HIGH WILL PUSH THE REMNANTS OF A FRONTAL BOUNDARY
ACROSS THE REGION, LEADING TO INCREASED SHOWERS AND THUNDERSTORMS.
AFTERNOON CONVECTION WILL ALSO AFFECT PORTIONS OF THE COASTAL WATERS.
ANY THUNDERSTORM ACTIVITY WILL LIKELY GENERATE LOCALLY HAZARDOUS
MARINE CONDITIONS FOR SMALL CRAFT. INCREASING WINDS AND A NORTHERLY
SWELL WILL LIKELY DETERIORATE MARINE CONDITIONS OVER THE WEEKEND.
BEACH FORECAST
INCREASING WINDS WILL LEAD TO MODERATE RISK FOR MOST NORTH- AND
EAST-FACING BEACHES, TODAY. DETERIORATING MARINE CONDITIONS WILL
BRING THE RISK OF RIP CURRENTS TO HIGH DURING THE WEEKEND. BE
AWARE THAT AFTERNOON THUNDERSTORMS POSE A THREAT OF LIGHTNING,
MOSTLY FOR THE BEACHES IN THE WEST AND SOUTHWESTERN COAST OF
PUERTO RICO.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM/AVIATION...LIS
LONG TERM/MARINE/BEACH FORECAST...MMC
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