189
FXCA62 TJSJ 270645
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
230 AM AST SUN SEP 27 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 208 AM AST SUN SEP 27 2026
- A HEAT ADVISORY WILL BE IN EFFECT FROM 9 AM THROUGH AT LEAST 4
PM AST TODAY ACROSS PUERTO RICO AND THE U.S. VIRGIN ISLANDS.
NONETHELESS, LIMITED HEAT RISKS WILL PREVAIL DURING THE
WORKWEEK.
- AFTERNOON SHOWERS AND THUNDERSTORMS WILL PRODUCE AN ELEVATED
RISK OF URBAN AND SMALL STREAM FLOODING TODAY ACROSS INTERIOR,
NORTH-CENTRAL, AND WESTERN PUERTO RICO. WEAK TROPICAL WAVE WILL
ENHANCE THE POTENTIAL FOR SHOWER AND THUNDERSTORM ACTIVITY.
- A MODERATE RISK OF RIP CURRENTS ALONG NORTHWESTERN TO EASTERN
BEACHES OF PUERTO RICO AND THE NORTHERN U.S. VIRGIN ISLANDS
THROUGH TONIGHT. BRIEF HIGH RISK OF RIP CURRENTS ON MONDAY DUE
TO A SMALL NORTHERLY SWELL.
SHORT TERM(TODAY THROUGH TUESDAY)
ISSUED AT 208 AM AST SUN SEP 27 2026
MOSTLY CLEAR SKIES WILL PREVAIL THIS MORNING INTO THE EARLY
AFTERNOON, ALLOWING TEMPERATURES TO RISE QUICKLY. COMBINED WITH
THE AVAILABLE MOISTURE, THESE CONDITIONS WILL PROMOTE HEAT INDICES
AROUND 108 DEGREES FAHRENHEIT. THEREFORE, A HEAT ADVISORY WAS
ISSUED FROM 9 AM THROUGH 3 PM, TODAY. THOSE SPENDING TIME OUTDOORS
SHOULD STAY HYDRATED, TAKE FREQUENT BREAKS IN SHADED OR AIR-
CONDITIONED AREAS, AND LIMIT STRENUOUS ACTIVITIES DURING THE
HOTTEST HOURS. DESPITE THE RELATIVELY FAIR START, PASSING SHOWERS
WILL BECOME MORE FREQUENT ACROSS WINDWARD AREAS, WITH NUMEROUS
SHOWERS AND THUNDERSTORMS EXPECTED THIS AFTERNOON OVER THE
INTERIOR, AND EXTENDING INTO THE NORTHERN AND WESTERN TO
NORTHWESTERN PORTIONS OF PUERTO RICO. STREAMERS MAY ALSO DEVELOP
DOWNWIND OF EL YUNQUE AND THE U.S. VIRGIN ISLANDS. THIS INCREASE
IN ACTIVITY WILL BE ASSOCIATED WITH AN APPROACHING TROPICAL WAVE,
WHICH IS EXPECTED TO REMAIN MAINLY SOUTH OF THE REGION, AND A
NEARBY UPPER-LEVEL TROUGH. LATEST MODEL GUIDANCE SUGGESTS A SLIGHT
INCREASE IN MOISTURE, ALTHOUGH PRECIPITABLE WATER VALUES SHOULD
REMAIN GENERALLY WITHIN SEASONAL RANGES. RELATIVELY STEEP MID-
LEVEL LAPSE RATES, SOME DRIER AIR ALOFT, AND STRONG DAYTIME
HEATING COULD SUPPORT LOCALLY STRONG THUNDERSTORMS CAPABLE OF
FREQUENT LIGHTNING, GUSTY WINDS, AND HEAVY DOWNPOURS. IN ADDITION,
THE STEERING FLOW WILL REMAIN RELATIVELY LIGHT THROUGH MUCH OF
THE DAY BEFORE GRADUALLY STRENGTHENING LATER TODAY. AS A RESULT,
THUNDERSTORMS COULD MOVE SLOWLY OR REGENERATE OVER THE SAME AREAS,
INCREASING THE POTENTIAL FOR LOCALLY EXCESSIVE RAINFALL.
THEREFORE, AN ELEVATED FLOODING RISK WILL PERSIST, WITH URBAN AND
SMALL-STREAM FLOODING, RAPID RISES ALONG SUSCEPTIBLE RIVERS, AND
HAZARDOUS DRIVING CONDITIONS POSSIBLE. SATURATED SOILS WILL ALSO
REMAIN VULNERABLE TO LANDSLIDES IN STEEP TERRAIN. A LIMITED
LIGHTNING RISK WILL ACCOMPANY THE STRONGER THUNDERSTORMS. PEOPLE
SHOULD REMAIN ALERT TO CHANGING WEATHER CONDITIONS THIS AFTERNOON,
SEEK SHELTER WHEN THUNDERSTORMS APPROACH, AND NEVER ATTEMPT TO
CROSS FLOODED ROADS.
ON MONDAY, PERIODS OF PASSING SHOWERS WILL CONTINUE, PARTICULARLY
ACROSS WINDWARD AREAS DURING THE MORNING, FOLLOWED BY AFTERNOON
CONVECTION OVER THE INTERIOR AND WESTERN TO NORTHWESTERN PUERTO
RICO. THEREFORE, MONDAY MAY REMAIN RELATIVELY ACTIVE, ALTHOUGH
SOMEWHAT DRIER AIR AND A STRENGTHENING EAST-SOUTHEASTERLY STEERING
FLOW SHOULD ALLOW SHOWERS AND THUNDERSTORMS TO MOVE QUICKLY OUT
OF THE AREA. THIS SHOULD LIMIT THE DURATION OF HEAVY RAINFALL OVER
JUST ONE PLACE COMPARED WITH TODAY, BUT LOCALLY HEAVY DOWNPOURS
AND LOCALIZED URBAN AND SMALL-STREAM FLOODING WILL REMAIN
POSSIBLE, ESPECIALLY WHERE SOILS REMAIN SATURATED FROM PREVIOUS
RAINFALL. RESIDENTS IN FLOOD AND LANDSLIDE PRONE AREAS SHOULD
CONTINUE TO MONITOR CONDITIONS, PARTICULARLY WHERE SIGNIFICANT
RAINFALL OCCURS TODAY.
BY TUESDAY, A MORE NOTICEABLE DRYING TREND IS EXPECTED AS
PRECIPITABLE WATER DECREASES BELOW TYPICAL LATE-SEPTEMBER VALUES
AND CONSIDERABLY DRIER AIR SPREADS THROUGH THE MID LEVELS. MOST
AVAILABLE MOISTURE SHOULD BECOME CONFINED TO THE LOWER LEVELS,
LIMITING THE DEPTH AND COVERAGE OF CONVECTION. BRIEF PASSING
SHOWERS WILL REMAIN POSSIBLE ACROSS WINDWARD AREAS, WITH ISOLATED
TO SCATTERED AFTERNOON SHOWERS MAINLY OVER WESTERN PUERTO RICO,
BUT OVERALL ACTIVITY AND RAINFALL AMOUNTS SHOULD DECREASE. AS A
RESULT, THE FLOODING THREAT SHOULD BECOME LIMITED, WITH LONGER
PERIODS OF FAIR WEATHER EXPECTED ACROSS MUCH OF THE REGION.
HEAT WILL REMAIN A CONCERN THROUGH THE NEXT SEVERAL DAYS. WHILE
TODAYS HEAT THREAT IS MORE WIDESPREAD, SUPPORTING AN ELEVATED HEAT
RISK, THE THREAT SHOULD BECOME MORE LOCALIZED MONDAY AND TUESDAY,
WHEN A LIMITED HEAT RISK IS ANTICIPATED. HOWEVER, AREAS THAT
EXPERIENCE PROLONGED PERIODS OF SUNSHINE COULD STILL OBSERVE
POTENTIALLY HAZARDOUS HEAT INDICES. THEREFORE, RESIDENTS AND
VISITORS ARE ENCOURAGED TO CONTINUE MONITORING THE LATEST
FORECASTS AND ADVISORIES, STAY HYDRATED, TAKE FREQUENT BREAKS FROM
THE HEAT, AND LIMIT PROLONGED OUTDOOR EXPOSURE DURING THE HOTTEST
PART OF THE DAY.
LONG TERM(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 208 AM AST SUN SEP 27 2026
NEAR A SEASONAL WEATHER PATTERN IS EXPECTED TO PERSIST IN THE LONG-
TERM FORECAST, INCREASING THE FLOODING THREAT BY THE END OF THE
WEEK. A SURFACE HIGH PRESSURE BUILDING OVER THE WESTERN ATLANTIC MAY
LINGER THROUGHOUT THE FORECAST PERIOD, LEADING TO AN E-ESE WINDFLOW,
AND BREEZY CONDITIONS ACROSS COASTAL AREAS OF THE ISLANDS. ACCORDING
TO THE DETERMINISTIC GUIDANCE OF THE GFS AND ECMWF, PWAT VALUES
SHOULD RANGE BETWEEN 1.4 AND 1.6, UNUSUAL FOR THIS TIME OF THE YEAR.
MOISTURE CONTENT IN THE LOW LEVELS SHOULD INCREASE BY FRIDAY, WITH
PWATS REACHING NORMAL VALUES (1.6 - 1.8 INCHES). IN THE MID TO UPPER
LEVELS, THE PRESENCE OF A TUTT EAST OF THE CWA AND A RIDGE ACROSS
THE CENTRAL CARIBBEAN WILL VARY THE WEATHER CONDITIONS ACROSS THE
ISLANDS. BASED ON THE LATEST MODEL GUIDANCE, THE RIDGE AND THE
SUBSIDENCE SIDE OF TROUGH OVER THE REGION SHOULD INCREASE STABILITY
ALOFT AND LIMIT DEEPER CONVECTION, PARTICULARLY ON WEDNESDAY AND
THURSDAY. BY FRIDAY INTO SATURDAY, THE RIDGE MAY WEAKEN, AS THE
UPPER-LEVEL TROUGH MIGRATED WESTWARD, POSITIONING OVER THE CWA AND
INTRODUCING INSTABILITY. ACCORDING TO THE LATEST GALVEZ-DAVISON
INDEX (GDI) SOLUTION, THE LIKELIHOOD OF ISOLATED TO SCATTERED
THUNDERSTORMS SHOULD INCREASE BY FRIDAY AND SATURDAY AFTERNOON.
UNDER THIS SCENARIO, CONDITIONS MAY BECOME FAVORABLE FOR LONG-
LASTING SHOWERS AND THUNDERSTORMS IN THE AFTERNOONS. IN GENERAL, THE
COMBINATION OF LOCAL EFFECTS, SEA BREEZE CONVERGENCE, AND DAYTIME
HEATING SHOULD TRIGGER THE AFTERNOON CONVECTION AND LOCAL ISLAND
STREAMERS EACH DAY, WITH THE BEST FLOODING CHANCE ACROSS INTERIOR
AND WESTERN NORTHWESTERN PUERTO RICO. ON WEDNESDAY AND THURSDAY,
RAINFALL ACCUMULATIONS COULD LEAD WITH MAINLY PONDING OF WATER OVER
ROADWAYS AND POORLY DRAINED AREAS, WHILE THE FLOODING THREAT SHOULD
INCREASE ON FRIDAY AND SATURDAY.
UNDER A E-ESE WINDFLOW, SEASONAL TO SLIGHTLY WARMER CONDITIONS CAN
BE EXPECTED IN THE LONG-TERM. WITH THE AVAILABLE MOISTURE, HEAT
INDICES MAY EXCEED 100 F, PARTICULARLY ACROSS URBAN AND LOW-LYING
AREAS. THEREFORE, THE HEAT THREAT SHOULD REMAIN LIMITED TO ELEVATED
THROUGHOUT THE FORECAST PERIOD, WITH WARMER CONDITIONS ON FRIDAY.
AVIATION
(06Z TAFS)
ISSUED AT 208 AM AST SUN SEP 27 2026
ALL TAF SITES SHOULD EXPERIENCE VFR CONDS THRU 27/15Z. AFTN
SHRA/TSRA DEVELOPMENT COULD RESULT IN VCTS AT TJBQ/TJPS BTW
27/16-23Z. BRIEF PERIODS OF MVFR PSBL ACROSS CENTRAL AND WESTERN
PR, PARTICULARLY AT TJPS/TJBQ AFT 27/17Z. E/SE WINDS FROM 5-10 KT
WITH HIGHER GUSTS AND SEA BREEZE VARIATIONS THRU 27/23Z.
MARINE
ISSUED AT 208 AM AST SUN SEP 27 2026
MODERATE EASTERLY WINDS WILL PREVAIL TODAY AND
STRENGTHEN SOMEWHAT TONIGHT INTO EARLY THIS WEEK. A NORTHERLY SWELL
WILL CONTINUE TO SPREAD ACROSS THE ATLANTIC WATERS AND PASSAGES,
COMBINING WITH THE INCREASING TRADE WINDS TO PRODUCE CHOPPY AND
GRADUALLY DETERIORATING MARINE CONDITIONS. SEAS WILL BUILD THROUGH
MONDAY, PARTICULARLY ACROSS THE NORTHERN WATERS AND PASSAGES. SMALL
CRAFT SHOULD EXERCISE CAUTION ACROSS PORTIONS OF THE ATLANTIC WATERS
AND LOCAL PASSAGES. PERIODS OF SHOWERS WILL CONTINUE, WITH ISOLATED
THUNDERSTORMS PRODUCING LOCALLY HIGHER WINDS AND SEAS, LIGHTNING,
AND REDUCED VISIBILITY.
BEACH FORECAST
ISSUED AT 208 AM AST SUN SEP 27 2026
A MODERATE RISK OF RIP CURRENTS WILL CONTINUE
TODAY ALONG THE WEST THROUGH NORTHEASTERN BEACHES OF PUERTO RICO, AS
WELL AS CULEBRA AND THE U.S. VIRGIN ISLANDS. CONDITIONS WILL BECOME
MORE HAZARDOUS MONDAY AS A NORTHERLY SWELL BUILDS AND WINDS
INCREASE, WITH A HIGH RISK OF RIP CURRENTS LIKELY ALONG PORTIONS OF
THE NORTHWESTERN THROUGH NORTHERN COAST OF PUERTO RICO. MODERATE
RISK CONDITIONS WILL CONTINUE ELSEWHERE ACROSS EXPOSED ATLANTIC
BEACHES. ADDITIONAL HAZARDS INCLUDE HEAT AND AFTERNOON
THUNDERSTORMS, PARTICULARLY ACROSS WESTERN PUERTO RICO.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY FROM 9 AM THIS MORNING TO 4 PM AST THIS AFTERNOON
FOR PRZ001>013.
VI...HEAT ADVISORY FROM 9 AM THIS MORNING TO 4 PM AST THIS AFTERNOON
FOR VIZ001-002.
AM...NONE.
SHORT TERM/AVIATION...MMC
LONG TERM...MNG
MARINE/BEACH FORECAST...ICP
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