940
FXCA62 TJSJ 281345
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
945 AM AST TUE OCT 28 2025
..UPDATE
WITH HURRICANE MELISSA TRACKING FARTHER WESTWARD OVERNIGHT, A MID-
TO UPPER-LEVEL RIDGE EXPANDED WESTWARD OVER THE NORTHEASTERN
CARIBBEAN EARLIER THAN ANTICIPATED, PROMOTING DRYING AND EROSION
OF MID- TO UPPER-LEVEL MOISTURE AND THUS UNFAVORABLE CONDITIONS
FOR DEEP CONVECTIVE DEVELOPMENT, EVEN THOUGH LINGERING LOW-LEVEL
MOISTURE REMAINS IN PLACE. THE DRYING OCCURRED EARLIER THAN
EXPECTED, AS SHOWN IN RADAR AND SATELLITE IMAGERY DISPLAYING
LIMITED SHOWER ACTIVITY AND INCREASING CLEAR SKIES. THE 28/12Z
SOUNDING SUPPORTS THIS TREND, SHOWING A PWAT OF 1.87 INCHES,
NEARLY HALF AN INCH LOWER THAN THE 28/00Z SOUNDING, CONFIRMING A
NOTABLE REDUCTION IN MID- TO UPPER-LEVEL MOISTURE.
AS A RESULT, THE FORECAST WAS UPDATED TO REFLECT LESS AREAL
COVERAGE, FREQUENCY, AND INTENSITY OF SHOWERS, LEADING TO LOWER
RAINFALL TOTALS AND FLOODING IMPACTS FOR TODAY. STILL, LIMITED
FLOODING POTENTIAL CONTINUES ACROSS SOUTHERN AND FAR NORTHWESTERN
PUERTO RICO, WHERE LINGERING LOW-LEVEL MOISTURE, DIURNAL HEATING,
AND LOCAL EFFECTS MAY TRIGGER BRIEF HEAVY SHOWERS OR AN ISOLATED
THUNDERSTORM THROUGH THIS EVENING. IN TERMS OF HEAT, CLEARER SKIES
HAVE LED TO HIGHER TEMPERATURES, BUT MOISTURE EROSION HAS REDUCED
RELATIVE HUMIDITY, WITH READINGS 4–6°F HIGHER AND 10–20% LOWER,
RESPECTIVELY, COMPARED TO YESTERDAY. THEREFORE, THE EXTREME HEAT
RISK REMAINS WITHIN THE LIMITED CATEGORY FOR TODAY.
KEY MESSAGES
* SHOWERS AND FEW ISOLATED THUNDERSTORMS ARE EXPECTED TO DEVELOP
THIS AFTERNOON OVER CENTRAL PUERTO RICO EARLY THIS AFTERNOON AND
SPREADING TOWARD THE WESTERN PORTIONS OF PUERTO RICO.
THEREFORE, MAINTAINING A LIMITED TO ELEVATED FLOODING RISK FOR
THESE AREAS.
* ACROSS THE U.S. VIRGIN ISLANDS, OCCASIONAL PASSING SHOWERS AND
FEW ISOLATED THUNDERSTORM ARE EXPECTED, MAINLY DURING THE
MORNING HOURS.
* BUILDING NORTHERLY SWELLS WILL LEAD TO ROUGHER SEAS AND
INCREASING RIP CURRENT RISKS, BECOMING HIGH ALONG NORTH-FACING
BEACHES BY WEDNESDAY.
SHORT TERM...TODAY THROUGH THURSDAY
(TODAY THROUGH THURSDAY)
ISSUED AT 321 AM AST TUE OCT 28 2025
OVERNIGHT, GOES-19 IMAGERY DETECTED A LAYER OF MID- TO UPPER-LEVEL
CLOUDS MOVING MAINLY ACROSS PUERTO RICO, AND THE DOPPLER RADAR
DETECTED A FEW SHOWERS AFFECTING THE SOUTHEAST AND SOUTHERN
MUNICIPALITIES. BY EARLY MORNING, MOST OF THE CLOUDINESS HAD
DISSIPATED, LEAVING PARTLY CLOUDY SKIES ACROSS MUCH OF THE ISLAND.
MEANWHILE, THE US VIRGIN ISLANDS OBSERVED A MIX OF CLOUDS AND CLEAR
SKIES. WINDS WERE GENERALLY FROM THE EAST-SOUTHEAST AT LESS THAN 10
MPH, AND LOW TEMPERATURES RANGED FROM THE MID TO UPPER 70S ALONG
COASTAL AREAS TO THE UPPER 60S ACROSS THE HIGHER ELEVATIONS.
LOCAL WEATHER CONDITIONS FOR PUERTO RICO AND THE US VIRGIN ISLANDS
WILL CONTINUE UNDER THE INFLUENCE OF MAJOR HURRICANE MELISSA (WHICH
IS SLOWLY APPROACHING JAMAICA), A BROAD HIGH-PRESSURE SYSTEM OVER
THE CENTRAL ATLANTIC, AND A WEAK FRONTAL BOUNDARY EXTENDING FROM THE
WESTERN ATLANTIC INTO THE SOUTHEASTERN US, WITH SEVERAL LOW-PRESSURE
AREAS EMBEDDED ALONG THE BOUNDARY. THUS, ACROSS THE NORTHEASTERN
CARIBBEAN, INCLUDING PUERTO RICO AND THE US VIRGIN ISLANDS, THE
PRESSURE GRADIENT BETWEEN THE ATLANTIC RIDGE AND THE DISTANT
HURRICANE SUPPORTS A LIGHT TO MODERATE EAST-SOUTHEASTERLY FLOW. THIS
PATTERN CONTINUES TO TRANSPORT PATCHES OF LOW-LEVEL MOISTURE ACROSS
THE REGION. AS A RESULT, MUGGY, WARM TEMPERATURES WILL ONCE AGAIN
PREVAIL ACROSS THE AREA, WITH OCCASIONAL CLOUDS AND SHOWERS IN THE
WINDWARD AREAS. BY THE AFTERNOON, SHOWERS WILL INTENSIFY OVER THESE
LOCATIONS, AND OTHERS WILL MOVE FURTHER INLAND OVER THE INTERIOR AND
NORTHERN PORTIONS OF PR. AFTERNOON CONVECTION WILL BE ENHANCED BY
LOCAL SEA-BREEZE CONVERGENCE. SOME THUNDERSTORMS WILL PRODUCE BRIEF
GUSTY WINDS AND MINOR FLOODING, MAINLY IN AREAS WITH HEAVIER
RAINFALL.
FROM TONIGHT THROUGH THURSDAY, THE WEATHER IN PUERTO RICO AND THE US
VIRGIN ISLANDS WILL BE GENERALLY WARM AND HUMID AS HURRICANE MELISSA
MOVES NORTHWARD, BRINGING SIGNIFICANT TROPICAL MOISTURE TO THE
REGION DUE TO SOUTHEASTERLY WIND FLOW. AT THE SAME TIME, A RIDGE IN
THE UPPER ATMOSPHERE IS DEVELOPING OVER THE AREA. THIS COMBINATION
WILL GRADUALLY INHIBIT DEEP CONVECTION BUT WILL STILL ALLOW FOR
PATCHES OF LOW-LEVEL MOISTURE, LEADING TO OCCASIONAL TRADE-WIND
SHOWERS AND A FEW ISOLATED THUNDERSTORMS IN THE AFTERNOONS AND
EVENINGS, PARTICULARLY IN THE MOUNTAINOUS AREAS OF PUERTO RICO AND
SURROUNDING WATERS. WHILE WIDESPREAD RAINFALL IS NOT EXPECTED, BRIEF
HEAVY DOWNPOURS AND LOCALIZED FLOODING MAY OCCUR WITH THE STRONGEST
SHOWERS EACH DAY.
WINDS WILL CONTINUE TO VEER FROM THE EAST-SOUTHEAST TONIGHT TO SOUTH-
SOUTHEAST BY THURSDAY, MAINTAINING MUGGY CONDITIONS AND ELEVATED
HEAT INDICES DURING THE PEAK OF HEATING. BY WEDNESDAY AFTERNOON, A
TIGHTENING PRESSURE GRADIENT BETWEEN MELISSA AND THE ATLANTIC RIDGE
WILL LIKELY RESULT IN BREEZY TO LOCALLY WINDY CONDITIONS,
PARTICULARLY ALONG THE COASTS AND OVER THE LOCAL WATERS.
LONG TERM...FRIDAY THROUGH TUESDAY
(THURSDAY THROUGH MONDAY)
ISSUED AT 321 AM AST TUE OCT 28 2025
THE CURRENT LONG-TERM FORECAST REMAINS ON TRACK. THE REGIONAL
WEATHER WILL BE INFLUENCED BY THE TRAILING MOISTURE ASSOCIATED WITH
HURRICANE MELISSA, WHICH BY NEXT WEEK IS EXPECTED TO BE LOCATED WELL
TO THE NORTH OF THE FORECAST AREA. WHILE THE BULK OF THIS MOISTURE
IS EXPECTED TO REMAIN OVER THE MONA CHANNEL AND NEAR HISPANIOLA,
SUFFICIENT RESIDUAL MOISTURE, WHEN COMBINED WITH DAYTIME HEATING AND
LOCALIZED EFFECTS, IS ANTICIPATED TO SUPPORT THE DEVELOPMENT OF
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE REGION, PRIMARILY
DURING THE AFTERNOON HOURS. AT THE SURFACE, A DOMINANT HIGH-PRESSURE
SYSTEM WILL MAINTAIN AN EAST TO SOUTHEAST WIND FLOW ACROSS THE AREA
THROUGH THE BEGINNING OF NEXT WEEK.
A SIGNIFICANT SHIFT IN CONDITIONS IS EXPECTED FROM LATE SATURDAY
INTO SUNDAY WITH THE APPROACH OF A TROPICAL WAVE FORECAST TO REMAIN
SOUTH OF THE ISLANDS. THE NORTHERN PERIPHERY OF THIS WAVE WILL
INCREASE MOISTURE, THEREFORE, INCREASING THE POTENTIAL FOR SHOWERS
AND THUNDERSTORMS, PARTICULARLY OVER THE CENTRAL MOUNTAIN RANGE AND
THE WESTERN PORTIONS OF THE ISLANDS. MODEL GUIDANCE INDICATES THAT
PRECIPITABLE WATER (PWAT) VALUES WILL RISE TO ABOVE-NORMAL
CLIMATOLOGICAL LEVELS, RANGING BETWEEN 2.00 AND 2.25 INCHES DURING
THIS PERIOD.
FOLLOWING THE PASSAGE OF THE TROPICAL WAVE, A DRAMATIC CHANGE IS
EXPECTED ON MONDAY. PWAT VALUES ARE FORECAST TO DROP SHARPLY TO
BELOW-NORMAL LEVELS, NEAR 1.25 INCHES. THIS SIGNIFICANT DECREASE
SIGNALS THE INFLUX OF A MUCH DRIER AND MORE STABLE AIR MASS, DRIVEN
BY THE POSITIONING OF A HIGH-PRESSURE SYSTEM ACROSS ALL ATMOSPHERIC
LEVELS TO THE NORTH OF THE LOCAL AREA.
THROUGHOUT THE FORECAST PERIOD, EXPECT ELEVATED HEAT CONDITIONS
DRIVEN BY ABOVE-NORMAL TEMPERATURES AT THE 925 MB LEVEL. MAXIMUM
TEMPERATURES ALONG THE COASTAL AND URBAN AREAS ARE FORECAST TO RANGE
FROM THE MID TO UPPER 80S. COOLER CONDITIONS ARE EXPECTED IN THE
MOUNTAINOUS REGIONS, WHERE MAXIMUM TEMPERATURES WILL REMAIN IN THE
MID 70S TO LOW 80S.
AVIATION
(06Z TAFS)
ISSUED AT 321 AM AST TUE OCT 28 2025
MAINLY VFR CONDS EXPECTED THRU PRD. BRIEF MVFR CONDS PSBL IN
SHRA/TSRA, WITH BRIEF REDNS IN VIS/CIGS MAINLY AFT 28/16-22Z,
AFFECTING TJPS/TJSJ. OCCASIONAL TRADE-WIND SHRA WILL AFFECT IST/ISX,
AND WE HAVE A SLIGHT TO MODERATE CHANCE TO SEE ISOLD TSRA DOWNWIND
FROM THE USVI AND NEAR JBQ BTWN (28/17-29/02Z). LGT/VRB WINDS THRU
28/13Z, THEN RETURNING FROM THE ESE AT 10–15 KT WITH SEA BREEZE
VARIATIONS. HIGHER GUSTS PSBL NR SHRA/TSRA.
MARINE
ISSUED AT 321 AM AST TUE OCT 28 2025
MODERATE TO LOCALLY FRESH SOUTHEASTERLY TO SOUTH WINDS WILL
PREVAIL FOR MOST OF THE WORKWEEK DUE TO MAJOR HURRICANE MELISSA
MOVING OVER JAMAICA INTO CUBA AND A HIGH PRESSURE BUILDS OVER THE
EASTERN CENTRAL ATLANTIC. SEAS WILL INCREASE TO CAUTIONARY LEVELS
BY WEDNESDAY ACCOMPANIED BY SHOWERS AND THUNDERSTORMS ASSOCIATED
WITH MELISSA'S MOISTURE FIELD LEADING TO PERIODS OF LOCALIZED
HAZARDOUS MARINE CONDITIONS.
BEACH FORECAST
ISSUED AT 321 AM AST TUE OCT 28 2025
A MODERATE RISK OF RIP CURRENTS WILL PERSIST TONIGHT ACROSS MOST
BEACHES OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS, WHERE LIFE-
THREATENING RIP CURRENTS REMAIN POSSIBLE. THE RISK WILL INCREASE TO
HIGH ON WEDNESDAY AND THURSDAY ALONG NORTH-FACING BEACHES OF PUERTO
RICO, CULEBRA, AND ST. CROIX, AS NORTHERLY SWELLS SPREAD ACROSS THE
LOCAL ATLANTIC WATERS AND PASSAGES, MAKING LIFE-THREATENING RIP
CURRENTS LIKELY FOR BEACHGOERS. A BRIEF IMPROVEMENT IS EXPECTED
THURSDAY NIGHT INTO FRIDAY, BEFORE CONDITIONS DETERIORATE AGAIN
DURING THE WEEKEND AS SWELLS FROM HURRICANE MELISSA REACH THE AREA.
IN ADDITION, SHOWERS AND ISOLATED THUNDERSTORMS MAY LOCALLY WORSEN
BEACH AND SURF CONDITIONS, BRINGING GUSTY WINDS, DANGEROUS
LIGHTNING, AND CHOPPY SURF THAT CAN QUICKLY MAKE SWIMMING UNSAFE.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HIGH RIP CURRENT RISK FROM 6 PM AST THIS EVENING THROUGH LATE
TONIGHT FOR PRZ001-002-005-008-012.
VI...NONE.
AM...NONE.
MORNING CREW...ICP/YZR
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