851
FXCA62 TJSJ 261757
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
157 PM AST SAT SEP 26 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 138 PM AST SAT SEP 26 2026
- 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
TOMORROW, SUNDAY.
- A HEAT ADVISORY REMAINS IN EFFECT THROUGH AT LEAST 4 PM AST TODAY
ACROSS COASTAL AND URBAN AREAS OF PUERTO RICO AND THE U.S. VIRGIN
ISLANDS. ELEVATED HEAT RISKS WILL PERSIST THROUGH THE WEEKEND.
- A MODERATE RISK OF RIP CURRENTS CONTINUES ALONG NORTHWESTERN TO
EASTERN BEACHES OF PUERTO RICO AND THE NORTHERN U.S. VIRGIN ISLANDS
THROUGH TOMORROW, SUNDAY. HIGH RISK OF RIP CURRENTS IS POSSIBLE ON
MONDAY DUE TO A SMALL NORTHERLY SWELL.
SHORT TERM(THIS EVENING THROUGH MONDAY)
ISSUED AT 138 PM AST SAT SEP 26 2026
AS EXPECTED, MOSTLY SUNNY SKIES PREVAILED THIS MORNING ACROSS THE
LOCAL AREA, WITH A FEW ISOLATED PASSING SHOWERS AFFECTING PORTIONS
OF THE U.S. VIRGIN ISLANDS (USVI) AND VERY ISOLATED SPOTS NEAR
EASTERN PUERTO RICO. THE MOSTLY SUNNY SKIES HAVE ALLOWED
TEMPERATURES TO RISE, WHICH, COMBINED WITH LIGHT EAST-SOUTHEASTERLY
WINDS AND AVAILABLE MOISTURE, IS DRIVING HEAT INDICES ABOVE 100
DEGREES ACROSS MANY COASTAL MUNICIPALITIES, AS WELL AS URBAN AREAS
AND VALLEYS ACROSS PUERTO RICO AND THE USVI. THE HEAT ADVISORY
REMAINS IN EFFECT THROUGH AT LEAST 4 PM AST THIS AFTERNOON.
THEREFORE, PEOPLE ARE URGED TO STAY WELL-HYDRATED AND TAKE BREAKS TO
ADEQUATELY COOL DOWN IF OUTSIDE.
COMPARED TO PREVIOUS DAYS, DRIER AIR IS BEING OBSERVED TODAY, WITH
THE 26/12Z TJSJ SOUNDING SHOWING A PRECIPITABLE WATER VALUE OF 1.56
INCHES, BELOW NORMAL FOR THIS TIME OF THE YEAR. THE SOUNDING ALSO
SHOWED A LIGHT SOUTHEASTERLY FLOW WITH WINDS OF 5 TO 6 KNOTS BETWEEN
THE SURFACE AND 3 KM, A VERY WEAK TO ABSENT LOW-LEVEL TEMPERATURE
INVERSION, A 500-MILLIBAR TEMPERATURE OF -7.3 DEGREES CELSIUS (NEAR
THE 25TH PERCENTILE FOR THIS PERIOD), AND A DCAPE OF AROUND 1100
J/KG. THESE CONDITIONS, COMBINED WITH AVAILABLE MOISTURE, STRONG
DAYTIME HEATING, AND LOCAL EFFECTS, WILL PROMOTE SHOWERS AND
THUNDERSTORMS DURING THE AFTERNOON ACROSS THE INTERIOR AND NORTH-
CENTRAL TO NORTHWESTERN QUADRANTS OF PUERTO RICO. DESPITE THE DRIER
AIR, MID- TO UPPER-LEVEL INSTABILITY ASSOCIATED TO THE CLOSE
PROXIMITY TO AN UPPER-LEVEL TROUGH CENTERED JUST EAST OF THE USVI,
SUPPORTS THE POTENTIAL FOR LOCALLY STRONG THUNDERSTORMS CAPABLE OF
PRODUCING FREQUENT LIGHTNING AND LOCALLY STRONG GUSTY WINDS ACROSS
SOME THOSE AREAS. ADDITIONALLY, THE LIGHT STEERING FLOW COULD
PRODUCE PROLONGED PERIODS OF RAINFALL AND, CONSIDERING RECENT RAINS
ACROSS THESE AREAS, WILL PROMOTE AN ELEVATED FLOOD RISK TODAY WITH
THE POTENTIAL FOR URBAN AND SMALL-STREAM FLOODING. STREAMERS WILL
CONTINUE TO BE POSSIBLE DOWNWIND FROM EL YUNQUE AND ALL THE
ISLANDS DURING THE AFTERNOON, WITH THE EL YUNQUE STREAMER FAVORING
THE POTENTIAL FOR SHOWER ACTIVITY ACROSS THE NORTHERN HALF OF THE
SAN JUAN METROPOLITAN AREA. OTHERWISE, MAINLY TRANQUIL WEATHER
CONDITIONS WILL CONTINUE. FOR TONIGHT, PASSING SHOWERS MAY AFFECT
PORTIONS OF EASTERN PUERTO RICO AND THE USVI, BUT NO SIGNIFICANT
IMPACTS ARE EXPECTED.
FOR SUNDAY, THE STEERING FLOW WILL SHIFT TO A MORE EAST-
SOUTHEASTERLY DIRECTION RATHER THAN SOUTHEASTERLY. SLIGHTLY HIGHER
MOISTURE, BUT STILL WITHIN SEASONAL VALUES, WILL ENTER THE REGION
DUE TO A TROPICAL WAVE PASSING MAINLY SOUTH OF OUR AREA, WHILE THE
UPPER-LEVEL TROUGH REMAINS JUST EAST OF THE LOCAL AREA. HENCE,
TOMORROW IS STILL EXPECTED TO BE THE MOST ACTIVE DAY IN TERMS OF
CONVECTIVE ACTIVITY, WITH THE POTENTIAL FOR MORE FREQUENT PASSING
SHOWERS IN WINDWARD AREAS THROUGHOUT THE DAY AND MORE NUMEROUS
SHOWERS AND THUNDERSTORMS IN THE AFTERNOON FAVORING THE WESTERN
INTERIOR AND WESTERN TO NORTHWESTERN QUADRANTS OF PUERTO RICO, AS
WELL AS AFTERNOON STREAMERS DOWNWIND FROM EL YUNQUE AND THE USVI.
SIMILAR TO TODAY, SOME THUNDERSTORM ACTIVITY COULD BE LOCALLY STRONG
WITH FREQUENT LIGHTNING AND GUSTY WINDS. HEAVY RAINFALL WILL POSE AN
ELEVATED FLOODING RISK, INCLUDING WATER ACCUMULATION ON ROADS AND
POORLY DRAINED AREAS, URBAN AND SMALL-STREAM FLOODING, AND QUICK
RISES ALONG SUSCEPTIBLE RIVERS. SATURATED TERRAIN WILL ALSO REMAIN
VULNERABLE TO LANDSLIDES.
BY MONDAY, A MORE TYPICAL WEATHER PATTERN WILL RETURN, WITH PASSING
MORNING SHOWERS OVER WINDWARD AREAS AND AFTERNOON CONVECTION
FAVORING INTERIOR, WESTERN, AND NORTHWESTERN PUERTO RICO. THE
RAINFALL HAZARD SHOULD BECOME MORE LOCALIZED DUE TO DRIER AIR AND A
STRONGER EAST-SOUTHEASTERLY STEERING FLOW.
AN ELEVATED HEAT THREAT WILL CONTINUE TO BE A CONCERN DURING THE
WARMEST HOURS THROUGH AT LEAST SUNDAY, AND IT COULD POSSIBLY
CONTINUE INTO MONDAY, ESPECIALLY WHERE PROLONGED MORNING AND EARLY-
AFTERNOON SUNSHINE OCCURS. FOR THAT REASON, WE URGE PEOPLE TO
MONITOR THE FORECAST AND PRACTICE HEAT SAFETY.
LONG TERM(TUESDAY THROUGH NEXT FRIDAY)
ISSUED AT 153 AM AST SAT SEP 26 2026
DRIER CONDITIONS THAN THOSE USUALLY SEEN FOR THE SEASON ARE EXPECTED
THROUGHOUT THE LONG TERM PERIOD. WHILE MODEL GUIDANCE INDICATES SOME
VARIABILITY, WITH THE GFS SHOWING MORE FAVORABLE CONDITIONS ON
TUESDAY, THE MAJORITY OF THE HUMIDITY WILL BE CENTERED IN THE LOW
LEVELS OF THE TROPOSPHERE WHILE DRIER CONDITIONS WILL DOMINATE THE
LOW-TO-UPPER LEVELS (700-250HPA). AN UPPER-LEVEL LOW PRESSURE SYSTEM
WILL BE LOCATED TO THE NORTHEAST OF THE US VIRGIN ISLANDS AND PUERTO
RICO AT THE BEGINNING OF THE WEEK AND WILL SHIFT TO THE SOUTHEAST OF
THE REGION BY THE END OF THE WEEK EVENTUALLY MOVING AWAY FROM THE
CWA BY THE END OF THE FORECAST PERIOD. WHILE THESE CONDITIONS WILL
ACT TO LIMIT SHOWER AND THUNDERSTORM ACTIVITY, OTHER FACTORS MAY
FAVOR MORE ACTIVE PERIODS OVER THE ISLANDS. MID TROPOSPHERIC
TEMPERATURES REMAIN FAVORABLE FOR THE DEVELOPMENT OF DEEP CONVECTIVE
CELLS. LOCAL EFFECTS WILL ACT AS THE MAIN DRIVERS OF ACTIVITY
PARTICULARLY OVER THE US VIRGIN ISLANDS AND EASTERN PUERTO RICO IN
THE MORNINGS AND THE INTERIOR AND NORTHWESTERN PUERTO RICO IN THE
AFTERNOONS. INCREASING SURFACE WINDS MAY ALSO FAVOR THE DEVELOPMENT
OF STREAMERS FROM THE US VIRGIN ISLANDS, VIEQUES, CULEBRA AND EL
YUNQUE RAINFOREST. CONDITIONS ARE EXPECTED TO BECOME MORE ENHANCED
BY FRIDAY AFTERNOON WHEN A MORE HUMID VERTICAL PROFILE RETURNS
INCREASING THE POTENTIAL FOR THE DEVELOPMENT OF CONVECTION. CITIZENS
AND VISITORS ARE INVITED TO REMAIN WEATHER READY AND STAY UPDATED OF
THE EVOLVING WEATHER CONDITIONS.
THE LONG TERM PERIOD MIGHT ALSO BRING A RESPITE FROM THE ELEVATED
HEAT RISKS AND THE 925 MB TEMPERATURES SHOW A DECREASING TREND,
SUGGESTING MORE AMENABLE CONDITIONS MIGHT PREVAIL AS THE WEEK
PROGRESSES. NONETHELESS, INDIVIDUALS ARE RECOMMENDED TO STAY ALERT
AS THESE FORECASTED CONDITIONS MAY CHANGE.
AVIATION
(18Z TAFS)
ISSUED AT 138 PM AST SAT SEP 26 2026
MAINLY VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS ALL TERMINALS
DURING THE NEXT 24 HOURS. HOWEVER, LOCALLY INDUCED AFTERNOON
TSRA/SHRA MAY DEVELOP IN AND AROUND TJBQ/TJSJ BTW 26/19-22Z. THE
26/12Z TJSJ SOUNDING INDICATED ESE WINDS UP TO 10 KT BLO FL050.
MARINE
ISSUED AT 138 PM AST SAT SEP 26 2026
LIGHT TO MODERATE EAST TO SOUTHEAST WINDS OF 10 TO 15 KNOTS OR LESS
AND SEAS GENERALLY BETWEEN 2 AND 4 FEET WILL PREVAIL TODAY. MARINE
CONDITIONS WILL GRADUALLY DETERIORATE FROM SUNDAY INTO EARLY NEXT
WEEK AS A NORTHERLY SWELL SPREADS ACROSS THE ATLANTIC WATERS AND
PASSAGES WHILE EASTERLY WINDS STRENGTHEN. SEAS WILL BUILD TO 5 TO 6
FEET ACROSS PORTIONS OF THE ATLANTIC WATERS AND LOCAL PASSAGES, WITH
OCCASIONAL SEAS UP TO 8 FEET POSSIBLE BY MONDAY NIGHT. SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS MAY ALSO RESULT IN LOCALLY
HIGHER WINDS AND SEAS, FREQUENT LIGHTNING, AND BRIEF REDUCTIONS IN
VISIBILITY DURING THE AFTERNOONS ACROSS THE WEST/NORTHWESTERN
WATERS OF PUERTO RICO.
BEACH FORECAST
ISSUED AT 138 PM AST SAT SEP 26 2026
A MODERATE RISK OF RIP CURRENTS WILL PREVAIL THROUGH THE WEEKEND
ALONG THE WEST THROUGH NORTHEASTERN BEACHES OF PUERTO RICO, AS
WELL AS CULEBRA AND THE U.S. VIRGIN ISLANDS. A HIGH RISK OF RIP
CURRENTS IS POSSIBLE BY MONDAY AS WINDS INCREASE SLIGHTLY ACROSS
THE ATLANTIC COASTAL WATERS, AND A SMALL NORTHERLY SWELL SPREADS
ACROSS THE ATLANTIC WATERS AND PASSAGES.
ADDITIONAL BEACH HAZARDS INCLUDE HEAT AND ISOLATED THUNDERSTORMS,
ESPECIALLY ACROSS WESTERN PUERTO RICO, WHERE LIGHTNING, BRIEF
HEAVY RAINFALL, AND GUSTY WINDS MAY OCCUR DURING THE AFTERNOON
HOURS.
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...RVM/MRR
AVIATION/BEACH/MARINE...DSR
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