836
FXCA62 TJSJ 271727
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
127 PM AST SUN SEP 27 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 108 PM AST SUN SEP 27 2026
- AFTERNOON SHOWERS AND THUNDERSTORMS WILL POSE AN ELEVATED FLOOD
RISK TODAY ACROSS THE INTERIOR TO NORTHWESTERN PUERTO RICO.
FLOOD THREATS WILL DIMINISH TO LIMITED ON MONDAY AND TUESDAY,
PRIMARILY PRESENTING A RISK OF ROADWAY PONDING.
- A HEAT ADVISORY REMAINS IN EFFECT THROUGH 4 PM AST TODAY FOR
PUERTO RICO AND THE U.S. VIRGIN ISLANDS. HEAT RISKS WILL EASE
STARTING MONDAY AS EASTERLY TRADE WINDS STRENGTHEN.
- A MODERATE RISK OF RIP CURRENTS CONTINUES ALONG NORTHWESTERN TO
EASTERN BEACHES OF PUERTO RICO AND THE NORTHERN U.S. VIRGIN
ISLANDS. A HIGH RISK OF RIP CURRENTS IS POSSIBLE ON MONDAY DUE
TO A SMALL NORTHERLY SWELL.
SHORT TERM(THIS EVENING THROUGH TUESDAY)
ISSUED AT 108 PM AST SUN SEP 27 2026
PARTLY TO MOSTLY SUNNY SKIES PREVAILED THIS MORNING ACROSS THE LOCAL
AREA, WITH ISOLATED PASSING SHOWERS IN PORTIONS OF THE U.S. VIRGIN
ISLANDS (USVI) AND EASTERN PUERTO RICO LEAVING MINIMAL
ACCUMULATIONS. THIS RESULTED IN AN ELEVATED HEAT THREAT TODAY, WITH
HEAT INDICES OVER 100 DEGREES FAHRENHEIT ACROSS MANY COASTAL AREAS
AND URBAN AREAS OF PUERTO RICO AND THE USVI, WITH SOME LOCATIONS
EXCEEDING 108 DEGREES. THE HEAT ADVISORY REMAINS IN EFFECT THROUGH
AT LEAST 4 PM AST THIS AFTERNOON. THOSE SPENDING TIME OUTDOORS
SHOULD STAY HYDRATED, TAKE FREQUENT BREAKS IN SHADED OR AIR-
CONDITIONED AREAS, AND LIMIT STRENUOUS ACTIVITIES DURING THE HOTTEST
HOURS. SOME HEAT RELIEF IS BEING OBSERVED IN AREAS EXPERIENCING
SHOWER ACTIVITY.
COMPARED TO PREVIOUS DAYS, THE LATEST 27/12Z TJSJ SOUNDING SHOWED A
SLIGHTLY STRONGER LOW-LEVEL STEERING FLOW, WITH A MEAN WIND OF 11
KNOTS FROM THE SURFACE TO 3 KM. PRECIPITABLE WATER REMAINS WITHIN
SEASONAL LEVELS AROUND 1.75 INCHES, ALTHOUGH SLIGHTLY HIGHER
MOISTURE CONTENT (BETWEEN 1.8 AND 1.9 INCHES) IS EXPECTED THIS
AFTERNOON AND TONIGHT AS MOISTURE EMBEDDED IN THE TRADE WINDS
(MAINLY INDUCED BY AN UPPER-LEVEL TROUGH JUST EAST OF THE LOCAL
AREA) ENTERS THE CWA FROM THE EAST. THIS MOISTURE, ALONG WITH
DIURNAL HEATING AND LOCAL EFFECTS, IS PROMOTING SHOWER ACTIVITY
ACROSS THE INTERIOR AND WESTERN TO NORTHWESTERN QUADRANTS OF PUERTO
RICO, WHERE AN ELEVATED FLOOD RISK WILL CONTINUE THROUGH THE
AFTERNOON. ISOLATED STRONG THUNDERSTORMS CANNOT BE RULED OUT.
STREAMERS WILL CONTINUE TO DEVELOP DOWNWIND FROM EL YUNQUE, VIEQUES,
CULEBRA, AND THE USVI. THIS WILL FAVOR THE POTENTIAL FOR SHOWERS AND
POSSIBLY ISOLATED THUNDERSTORMS ACROSS PORTIONS OF NORTHEASTERN
PUERTO RICO AND THE NORTHERN HALF OF THE SAN JUAN METROPOLITAN AREA,
WHERE A LIMITED FLOOD RISK EXISTS. AS MORE MOISTURE POOLS INTO THE
REGION, MORE FREQUENT PASSING SHOWERS ARE EXPECTED TO REACH PORTIONS
OF EASTERN PUERTO RICO AND THE USVI BEFORE A DRIER AIR MASS ARRIVES
OVERNIGHT INTO MONDAY MORNING.
ON MONDAY, A MORE SEASONAL WEATHER PATTERN IS EXPECTED WITH NORMAL
TO BELOW-NORMAL PRECIPITABLE WATER. EXPECT TYPICAL MORNING PASSING
SHOWERS ACROSS THE WINDWARD AREAS OF PUERTO RICO AND THE USVI,
FOLLOWED BY AFTERNOON CONVECTION ACROSS WESTERN INTERIOR, WESTERN,
AND NORTHWESTERN PUERTO RICO. STREAMERS COULD PROMOTE SHOWER
ACTIVITY DOWNWIND FROM EL YUNQUE INTO NORTHEASTERN PR AND DOWNWIND
FROM THE USVI. HOWEVER, OVERALL DRIER AIR AND A STRONGER EAST-
SOUTHEASTERLY STEERING FLOW SHOULD MAINTAIN A LIMITED FLOOD RISK FOR
MONDAY COMPARED TO TODAY. PARTLY TO MOSTLY SUNNY SKIES WITH LIMITED
SHOWER COVERAGE SHOULD PREVAIL OTHERWISE.
BY MONDAY NIGHT INTO TUESDAY, WINDS WILL SHIFT TO A MORE EASTERLY
DIRECTION AND STRENGTHEN, BRINGING HIGHER MOISTURE CONTENT (STILL
WITHIN SEASONAL VALUES) INTO THE LOCAL AREA. THIS WILL PROMOTE
SLIGHTLY MORE VARIABLE WEATHER CONDITIONS ACROSS THE FORECAST AREA,
WITH MORE FREQUENT PASSING SHOWERS REACHING THE USVI AND EASTERN AND
NORTHEASTERN PUERTO RICO. PONDING OF WATER ON ROADWAYS WILL BE
POSSIBLE WHERE THE MORE FREQUENT ACTIVITY OCCURS. IN THE AFTERNOON,
SHOWERS AND ISOLATED THUNDERSTORMS WILL DEVELOP ACROSS THE INTERIOR
INTO WESTERN PUERTO RICO, AS WELL AS DOWNWIND FROM EL YUNQUE AND THE
SMALLER ISLANDS DUE TO STREAMERS. HOWEVER, DUE TO THE STRONGER
STEERING FLOW, FLOOD RISK IS EXPECTED TO REMAIN LIMITED, WITH
PONDING OF WATER ON ROADWAYS IN AREAS OF HEAVIER ACTIVITY.
THE ELEVATED HEAT THREAT COULD DIMINISH AFTER TODAY AS WINDS
INCREASE IN SPEED AND SHIFT MORE EASTERLY OVER THE NEXT FEW DAYS.
THIS WILL FAVOR A MORE LIMITED HEAT RISK FROM MONDAY ONWARD,
BRINGING SLIGHT RELIEF FROM THE HOT CONDITIONS EXPERIENCED OVER THE
LAST FEW DAYS.
LONG TERM(WEDNESDAY THROUGH NEXT SATURDAY)
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
(18Z TAFS)
ISSUED AT 108 PM AST SUN SEP 27 2026
MAINLY VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS ALL TERMINALS
DURING THE NEXT 24 HOURS. HOWEVER, LOCALLY INDUCED AFTERNOON
TSRA/SHRA IN AND AROUND TJBQ/TJSJ MAY CAUSE TEMPO MVFR TO BRIEF
IFR CONDS THRU 27/22Z. THE 27/12Z TJSJ SOUNDING INDICATED ESE
WINDS UP TO 18 KNOTS BLO FL100.
MARINE
ISSUED AT 108 PM AST SUN SEP 27 2026
LIGHT TO MODERATE EAST TO SOUTHEAST WINDS WILL PREVAIL THROUGH
TONIGHT, AND STRENGTHEN TO AROUND 15 KNOTS THROUGH MIDWEEK, AS
THEY TURN MORE FROM THE EAST TO NORTHEAST. A SMALL NORTHERLY
SWELL WILL CONTINUE TO SPREAD ACROSS THE ATLANTIC WATERS AND
PASSAGES, COMBINING WITH THE INCREASING TRADE WINDS TO PRODUCE
CHOPPY CONDITIONS. SEAS WILL BUILD UP TO 6 FEET BY MONDAY,
PARTICULARLY ACROSS THE ATLANTIC WATERS. PERIODS OF SHOWERS AND
THUNDERSTORMS WILL CONTINUE DURING THE AFTERNOON/EVENING HOURS,
PRODUCING LOCALLY HIGHER WINDS AND SEAS, LIGHTNING, AND REDUCED
VISIBILITY.
BEACH FORECAST
ISSUED AT 108 PM 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 UNTIL 4 PM AST THIS AFTERNOON FOR PRZ001>013.
VI...HEAT ADVISORY UNTIL 4 PM AST THIS AFTERNOON FOR VIZ001-002.
AM...NONE.
SHORT TERM...KML
LONG TERM....MNG
AVIATION/MARINE/BEACH FORECAST...DSR
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