025
FXCA62 TJSJ 201702 CCA
AFDSJU
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SAN JUAN PR
102 PM AST SUN SEP 20 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 1254 PM AST SUN SEP 20 2026
- AFTERNOON SHOWERS AND THUNDERSTORMS MAY PRODUCE LOCALLY HEAVY
RAINFALL THAT COULD LEAD TO FLOODING, MAINLY ACROSS INTERIOR,
NORTHERN, AND WESTERN PUERTO RICO.
- A WETTER AND MORE UNSTABLE PATTERN IS EXPECTED MID TO LATE NEXT
WEEK, INCREASING THE POTENTIAL FOR MORE WIDESPREAD HEAVY RAINFALL
AND STRONGER THUNDERSTORMS.
- HOT AND HUMID CONDITIONS WILL CONTINUE THROUGH MUCH OF THE WEEK,
WITH HEAT CONCERNS EACH DAY BEFORE THE ONSET OF AFTERNOON
SHOWERS.
- A MODERATE RISK OF RIP CURRENTS IS EXPECTED FROM WEDNESDAY
ONWARD ACROSS THE NORTH AND EASTERN BEACHES OF THE ISLANDS.
SHORT TERM(THIS EVENING THROUGH TUESDAY)
ISSUED AT 1254 PM AST SUN SEP 20 2026
PARTLY TO MOSTLY CLEAR SKIES PREVAILED ACROSS THE REGION DURING
THE MORNING HOURS, ACCOMPANIED BY ISOLATED PASSING SHOWERS OVER
EASTERN AND SOUTHEASTERN PUERTO RICO, VIEQUES, CULEBRA, AND THE
U.S. VIRGIN ISLANDS. RAINFALL ACCUMULATIONS REMAINED MINIMAL IN
GENERAL, BUT THE DOPPLER RADAR ESTIMATED UP TO THREE QUARTERS OF
AN INCH IF RAIN IN CAROLINA. LIGHT TO MODERATE SOUTHEASTERLY
WINDS ARE DOMINATING THE AREA AT 5 TO 15 MPH WITH LOCAL SEA BREEZE
VARIATIONS. MAXIMUM TEMPERATURES SO FAR ARE IN THE UPPER 80S AND
LOW 90S ACROSS LOWER ELEVATIONS AND VALLEYS OF PUERTO RICO AND THE
USVI. A HEAT ADVISORY REMAINS IN EFFECT THROUGH 3 PM AST THIS
AFTERNOON.
THE 20/12Z TJSJ SOUNDING SHOWED A PRECIPITABLE WATER (PWAT) VALUE OF
1.91 INCHES, WHICH IS WITHIN THE NORMAL RANGE FOR THIS TIME OF YEAR,
ALONGSIDE A WEAK EAST-SOUTHEASTERLY STEERING FLOW OF AROUND 9 KNOTS
IN THE 1 TO 3 KM LAYER. THESE CONDITIONS WILL FAVOR LOCAL EFFECTS
PLAYING A DOMINANT ROLE IN SHOWER AND THUNDERSTORM DEVELOPMENT
TODAY, ESPECIALLY ACROSS INTERIOR, WESTERN, NORTH-CENTRAL, AND
NORTHWESTERN PUERTO RICO. AN ELEVATED FLOOD THREAT IS EXPECTED TODAY
IN THESE REGIONS, AS SLOW-MOVING OR REPEATED CONVECTION COULD
PRODUCE URBAN AND SMALL-STREAM FLOODING, ISOLATED FLASH FLOODING,
AND LANDSLIDES IN STEEP TERRAIN, PARTICULARLY WHERE SOILS REMAIN
SATURATED FROM RECENT HEAVY RAINFALL. STREAMERS HAVE ALSO DEVELOPED
DOWNWIND OF EL YUNQUE, VIEQUES, CULEBRA, AND ALL OF THE USVI. DUE TO
THE ESE TO SE WIND FLOW, THE EL YUNQUE STREAMER WILL SUPPORT SHOWER
AND THUNDERSTORM ACTIVITY ACROSS THE NORTHERN HALF OF THE SAN JUAN
METROPOLITAN AREA, LEADING TO POTENTIAL PONDING OF WATER ON ROADWAYS
AND IN POORLY DRAINED AREAS. SOME OF THIS ACTIVITY MAY PERSIST
INTO THE EVENING HOURS. HOWEVER, A SEASONAL PATTERN WILL RETURN
LATER THIS EVENING AND OVERNIGHT, BRINGING PASSING SHOWERS TO
PORTIONS OF THE USVI AS WELL AS EASTERN AND SOUTHEASTERN PUERTO
RICO.
ON MONDAY AND TUESDAY, WEAK MID-LEVEL RIDGING NORTH OF THE REGION
WILL HELP INTRODUCE SLIGHTLY DRIER AIR, THOUGH PWAT VALUES WILL
GENERALLY REMAIN BETWEEN 1.8 AND 2.0 INCHES. MEANWHILE, SURFACE HIGH
PRESSURE OVER THE ATLANTIC WILL BECOME BETTER ORGANIZED, CAUSING
WINDS TO GRADUALLY STRENGTHEN. DESPITE THE SUBTLE DRYING, SUFFICIENT
LOW-LEVEL MOISTURE COMBINED WITH STRONG DAYTIME HEATING WILL SUPPORT
ACTIVE AFTERNOONS ON BOTH DAYS. THE 500 MB TEMPERATURES WILL STAY
AROUND -6 DEGREES CELSIUS ON MONDAY BEFORE DECREASING TO -7 DEGREES
CELSIUS ON TUESDAY AS THE RIDGE RETREATS AND A MID- TO UPPER-LEVEL
TROUGH BEGINS TRANSITIONING THE PATTERN TOWARD GREATER INSTABILITY
TUESDAY NIGHT. THIS WILL SUPPORT DAILY THUNDERSTORM ACTIVITY, WITH
THE POTENTIAL FOR ISOLATED STRONG THUNDERSTORMS CAPABLE OF FREQUENT
LIGHTNING AND GUSTY WINDS. WINDS WILL SHIFT FROM SOUTHEASTERLY ON
MONDAY TO MORE EASTERLY ON TUESDAY, FOCUSING AFTERNOON CONVECTION
FROM THE INTERIOR INTO WESTERN PUERTO RICO WITH A MORE WESTWARD
STORM MOTION. MORE TRANQUIL CONDITIONS ARE EXPECTED EACH NIGHT AND
MORNING, WITH PASSING SHOWERS ACROSS PORTIONS OF EASTERN AND
SOUTHEASTERN PUERTO RICO AND THE USVI. THE DRIEST PERIOD IS EXPECTED
TUESDAY EVENING.
THE MAIN HAZARDS THROUGH THE PERIOD WILL CONTINUE TO BE HEAT,
LOCALLY HEAVY RAINFALL LEADING TO FLOODING, LIGHTNING, AND GUSTY
WINDS. HEAT CONCERNS WILL LIKELY PERSIST MONDAY AND TUESDAY ACROSS
PUERTO RICO AND THE USVI. THE GREATEST RAINFALL THREAT WILL OCCUR
DURING THE AFTERNOON HOURS, MAINLY SPANNING THE INTERIOR INTO THE
WESTERN AND NORTHWESTERN QUADRANTS OF PUERTO RICO, AND DOWNWIND FROM
EL YUNQUE.
LONG TERM(WEDNESDAY THROUGH NEXT SATURDAY)
ISSUED AT 145 AM AST SUN SEP 20 2026
AT THIS TIME, WEDNESDAY IS FORECAST TO CONTINUE THE TRANSITION TOWARD
A MORE UNSTABLE PATTERN AS THE MID- TO UPPER-LEVEL TROUGH EXERTS A
GREATER INFLUENCE ACROSS THE REGION. BY THURSDAY, A TROPICAL WAVE IS
EXPECTED TO REACH THE ISLANDS, PROVIDING ADDITIONAL MOISTURE AND
LOW-LEVEL SUPPORT WHILE CONDITIONS ALOFT BECOME INCREASINGLY
FAVORABLE FOR CONVECTION. THE LATEST MODEL GUIDANCE SHOWS MID-LEVEL
TEMPERATURES FALLING TO AROUND -9 DEGREES CELSIUS. WITH FAVORABLE
MID-LEVEL MOISTURE ALSO IN PLACE, THURSDAY INTO FRIDAY APPEARS TO BE
THE MOST FAVORABLE PERIOD FOR STRONGER CONVECTION.
MORE FREQUENT PASSING SHOWERS ARE EXPECTED ACROSS WINDWARD AREAS AND
THE U.S. VIRGIN ISLANDS, WHILE AFTERNOON THUNDERSTORMS ACROSS PUERTO
RICO COULD PRODUCE HEAVY RAINFALL, FREQUENT LIGHTNING, AND LOCALLY
GUSTY WINDS. AN ELEVATED FLOODING RISK IS POSSIBLE DURING THIS PERIOD,
PARTICULARLY ACROSS URBAN AREAS, SMALL STREAMS, AND LOCATIONS
RECEIVING REPEATED HEAVY RAINFALL.
ALTHOUGH INSTABILITY ALOFT WILL PERSIST INTO SATURDAY, GUIDANCE
INDICATES THAT MID-LEVEL MOISTURE WILL BEGIN TO DECREASE,
PARTICULARLY WITHIN THE 700-500 MB LAYER. AFTERNOON THUNDERSTORMS
WILL REMAIN POSSIBLE, ESPECIALLY ACROSS THE INTERIOR AND WESTERN
PORTIONS OF PUERTO RICO, BUT COVERAGE SHOULD BECOME MORE LOCALIZED AS
MOISTURE GRADUALLY DECREASES.
BY SUNDAY, ADDITIONAL MID-LEVEL DRYING IS ANTICIPATED WHILE
TEMPERATURES ALOFT REMAIN RELATIVELY COLD AND LAPSE RATES REMAIN
FAVORABLE. THEREFORE, SUFFICIENT INSTABILITY SHOULD REMAIN FOR
AFTERNOON CONVECTION, ALTHOUGH REDUCED MOISTURE SHOULD LIMIT BOTH
THUNDERSTORM COVERAGE AND LIGHTNING ACTIVITY COMPARED WITH THURSDAY
AND FRIDAY. LOW-LEVEL WINDS ARE ALSO EXPECTED TO STRENGTHEN SOMEWHAT
TOWARD THE END OF THE PERIOD.
HEAT RISK WILL REMAIN A CONCERN THROUGHOUT THE PERIOD, BUT IT WILL
LARGELY DEPEND ON CLOUD COVER AND THE COVERAGE AND TIMING OF SHOWERS
ASSOCIATED WITH THE UPPER-LEVEL TROUGH AND TROPICAL WAVE. GREATER
CLOUDINESS AND EARLIER RAINFALL COULD LIMIT DAYTIME HEATING IN SOME
AREAS, WHILE LOCATIONS EXPERIENCING LONGER PERIODS OF SUNSHINE COULD
REACH HIGHER HEAT INDICES. THEREFORE, RESIDENTS AND VISITORS SHOULD
CONTINUE MONITORING THE FORECAST AS CONFIDENCE INCREASES REGARDING
THE EVOLUTION OF THE TROUGH, TROPICAL WAVE, RAINFALL, AND HEAT
RISK.
AVIATION
(18Z TAFS)
ISSUED AT 1254 PM AST SUN SEP 20 2026
MAINLY VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS ALL TERMINALS
THROUGH MOST OF THE FORECAST PERIOD. HOWEVER, TEMPO MVFR TO BRIEF
IFR CONDS POSSIBLE AT TJSJ/TJBQ THRU 20/22Z DUE TO LOCALLY INDUCED
TSRA/SHRA. ACROSS THE USVI TERMINALS AND TJPS, MOSTLY VCSH EXPECTED.
THE 20/12Z TJSJ SOUNDING INDICATED ESE WINDS UP TO 12 KT BLO FL050.
A NORTHERLY COMPONENT DUE TO THE SEA BREEZE WILL CONTINUE AT
TJSJ/TJBQ WITH POSSIBLE STRONGER GUSTS THRU 20/21Z. LIGHT AND
VARIABLE WIND EXPECTED OVERNIGHT.
MARINE
ISSUED AT 1254 PM AST SUN SEP 20 2026
A WEAK PRESSURE GRADIENT ACROSS THE REGION WILL CONTINUE TO PROMOTE
LIGHT TO MODERATE TRADES. WINDS WILL GRADUALLY TURN MORE EAST TO
SOUTHEAST THROUGH MIDWEEK AS HIGH PRESSURE OVER THE NORTHEASTERN
ATLANTIC BECOMES BETTER ORGANIZED. SEAS WILL REMAIN AROUND 2 TO 4
FEET ACROSS THE ATLANTIC AND CARIBBEAN WATERS, INCLUDING THE LOCAL
PASSAGES. PASSING SHOWERS MAY BRIEFLY INCREASE WINDS AND SEAS, WHILE
AFTERNOON THUNDERSTORMS MOVING INTO THE ATLANTIC AND WESTERN COASTAL
WATERS OF PUERTO RICO MAY PRODUCE LOCALLY STRONG GUSTS, TORRENTIAL
RAINFALL, AND FREQUENT LIGHTNING THROUGH THE EARLY EVENING HOURS.
BEACH FORECAST
ISSUED AT 1254 PM AST SUN SEP 20 2026
A LOW RISK OF RIP CURRENTS IS EXPECTED TO CONTINUE ACROSS ALL
BEACHES OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS THROUGH MIDWEEK.
HOWEVER, EVEN WITH A LOW RISK, LIFE-THREATENING RIP CURRENTS CAN
OCCUR NEAR GROINS, JETTIES, REEFS, AND PIERS. FROM LATE WEDNESDAY
ONWARD, A MODERATE RISK IS EXPECTED TO RETURN ACROSS THE NORTH AND
EAST-FACING BEACHES OF THE ISLANDS, DUE TO A SMALL LONG-PERIOD
NORTHEASTERLY SWELL AND AS WINDS INCREASE SLIGHTLY ACROSS THE
COASTAL WATERS.
OTHER BEACH HAZARDS WILL BE HEAT, AND THUNDERSTORMS WITH GUSTY WINDS
AND LIGHTNING STRIKES DURING THE AFTERNOON HOURS. BEACHGOERS SHOULD
REMAIN HYDRATED AND LIMIT PROLONGED SUN EXPOSURE, AND SEEK SHELTER
WHENEVER THEY HEAR THUNDER.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY UNTIL 3 PM AST THIS AFTERNOON FOR PRZ001>013.
VI...HEAT ADVISORY UNTIL 3 PM AST THIS AFTERNOON FOR VIZ001-002.
AM...NONE.
SHORT TERM...KML
LONG TERM....MMC
AVIATION/BEACH/MARINE...DSR
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