884
FXCA62 TJSJ 211655
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1255 PM AST TUE JUL 21 2026
..NEW SHORT TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 1250 PM AST TUE JUL 21 2026
* ADDITIONAL SHOWERS AND THUNDERSTORMS THROUGH THIS AFTERNOON MAY
RESULT IN PONDING OF WATER ON ROADS AND LOCALIZED URBAN AND
SMALL-STREAM FLOODING, PARTICULARLY ACROSS SOUTHWESTERN PUERTO
RICO.
* ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS IS EXPECTED ON
WEDNESDAY. A SHIFT TO A MORE SOUTHEASTERLY WIND FLOW WILL FAVOR
ACTIVITY ACROSS THE NORTHERN HALF OF PUERTO RICO, INCLUDING THE
SAN JUAN METROPOLITAN AREA AND THE NORTHWESTERN MUNICIPALITIES.
* ACROSS THE U.S. VIRGIN ISLANDS, PASSING SHOWERS AND BRIEF
PERIODS OF GUSTY WINDS WILL CONTINUE THROUGH AT LEAST WEDNESDAY.
* HOTTER CONDITIONS ARE EXPECTED ON WEDNESDAY, WITH HEAT
ADVISORY/WARNING CRITERIA POSSIBLE ACROSS URBAN AND COASTAL
AREAS.
* HAZY SKIES ARE EXPECTED TO RETURN LATE THIS WEEK AS MODERATE
SAHARAN DUST CONCENTRATIONS MOVE INTO THE REGION.
SHORT TERM(THIS EVENING THROUGH THURSDAY)
ISSUED AT 1250 PM AST TUE JUL 21 2026
AN INDUCED SURFACE TROUGH BROUGHT SHOWERS AND THUNDERSTORMS
ACROSS THE NORTHERN HALF OF PUERTO RICO, EASTERN PUERTO RICO, AND
THE U.S. VIRGIN ISLANDS THIS MORNING, PRODUCING LOCALLY HEAVY
RAINFALL AND PONDING OF WATER IN SOME AREAS. THIS ACTIVITY WAS
FAST-MOVING. MEANWHILE, SOUTHERN PUERTO RICO REMAINED MOSTLY SUNNY
AND WARM, WITH MAXIMUM TEMPERATURES REACHING THE LOWER TO MID-90S
ALONG THE SOUTHERN COAST AND ACROSS THE USVI. IN CONTRAST,
NORTHERN COASTAL AREAS REMAINED IN THE MID TO UPPER 80S. NORTHEAST
WINDS PREVAILED AT 5 TO 15 MPH.
THIS AFTERNOON, DAYTIME HEATING, LOCAL SEA BREEZE CONVERGENCE,
AND LINGERING MOISTURE WILL SUPPORT ANOTHER ROUND OF SHOWERS AND
THUNDERSTORMS ACROSS THE INTERIOR AND SOUTHWESTERN PUERTO RICO,
WHILE A DRIER AIR MASS TRAILING THIS TROUGH WILL FILTER OVER THE
USVI AND THE REST OF PR. LOCALLY HEAVY RAINFALL MAY RESULT IN
PONDING OF WATER ON ROADS AND LOCALIZED URBAN AND SMALL-STREAM
FLOODING.
TONIGHT THROUGH WEDNESDAY, AN UPPER-LEVEL LOW NORTH OF THE REGION
AND THE INDUCED SURFACE TROUGH WILL MAINTAIN AN UNSETTLED
PATTERN. AS THE LOW-LEVEL FLOW SHIFTS TO THE EAST-SOUTHEAST,
SHOWER AND THUNDERSTORM ACTIVITY WILL BECOME MORE FOCUSED ACROSS
NORTHERN PUERTO RICO, INCLUDING THE SAN JUAN METROPOLITAN AREA AND
THE NORTHWESTERN MUNICIPALITIES. PASSING SHOWERS AND A FEW
ISOLATED THUNDERSTORMS WILL ALSO AFFECT THE U.S. VIRGIN ISLANDS
LATE TONIGHT INTO WEDNESDAY MORNING.
HOTTER CONDITIONS ON WEDNESDAY MAY PUSH HEAT INDICES INTO HEAT
ADVISORY TERRITORY ACROSS URBAN AND COASTAL AREAS. BY LATE
WEDNESDAY NIGHT INTO THURSDAY, A SAHARAN AIR LAYER WILL BRING A
DRIER AND MORE STABLE AIR MASS, RESULTING IN HAZY SKIES, DEGRADED
AIR QUALITY, AND LIMITED SHOWER ACTIVITY.
LONG TERM
ISSUED AT 331 AM AST TUE JUL 21 2026
BY THE END OF THE WEEK AND INTO THE WEEKEND, MODERATE CONCENTRATIONS
OF SAHARAN DUST ARE EXPECTED TO PERSIST ACROSS THE REGION. SURFACE
HIGH PRESSURE OVER THE ATLANTIC WILL REESTABLISH ITSELF AS THE UPPER-
LEVEL LOW WEAKENS AND MOVES AWAY, RESULTING IN BREEZY EASTERLY
WINDS, PARTICULARLY ON FRIDAY AND SATURDAY. DURING THIS PERIOD,
AVAILABLE MOISTURE WILL REMAIN PRIMARILY CONFINED TO THE SURFACE
THROUGH THE 850 MB LAYER, WITH PWAT VALUES FLUCTUATING BETWEEN 1.6
AND 1.9 INCHES. THESE VALUES ARE CONSIDERED SEASONAL FOR THIS TIME
OF YEAR BASED ON CLIMATOLOGY, ALTHOUGH LOCALLY ABOVE-NORMAL VALUES
MAY DEVELOP DURING AFTERNOON CONVECTION. THE EASTERLY STEERING FLOW
WILL CONTINUE TO FAVOR PASSING SHOWERS ACROSS WINDWARD AREAS DURING
THE NIGHTTIME AND MORNING HOURS, FOLLOWED BY AFTERNOON SHOWERS OVER
WESTERN PUERTO RICO DRIVEN BY LOCAL EFFECTS AND AVAILABLE MOISTURE.
THE FLOOD RISK IS EXPECTED TO REMAIN LOW, ALTHOUGH A FEW ISOLATED
THUNDERSTORMS WILL REMAIN POSSIBLE EACH AFTERNOON ACROSS WESTERN
PUERTO RICO. TEMPERATURES AT 500 MB WILL REMAIN AROUND -6 TO -7 °C,
WHICH IS NEAR CLIMATOLOGICAL NORMAL, BUT STILL SUFFICIENT TO SUPPORT
ISOLATED THUNDERSTORMS ASSOCIATED WITH AFTERNOON CONVECTION.
FROM SUNDAY THROUGH TUESDAY, CURRENT GUIDANCE SUGGESTS THAT MOISTURE
ASSOCIATED WITH A TROPICAL WAVE AND AN ACCOMPANYING WIND SURGE WILL
REACH THE AREA, INCREASING PWAT VALUES TO ABOVE-NORMAL LEVELS WHILE
PRODUCING BREEZY TO LOCALLY WINDY EAST-SOUTHEASTERLY FLOW. PWAT
VALUES ARE EXPECTED TO REMAIN ABOVE 1.8 INCHES FROM SUNDAY ONWARD,
PEAKING AROUND 2.1 INCHES BETWEEN MONDAY AND TUESDAY (NEAR THE 75TH
PERCENTILE). ADDITIONALLY, CURRENT MODEL GUIDANCE INDICATES THAT AN
UPPER-LEVEL LOW WILL DEVELOP AND MOVE ACROSS THE NORTHEASTERN
CARIBBEAN. THIS IS REFLECTED BY LOWER 250 MB HEIGHTS AND COOLER 500
MB TEMPERATURES, BOTH DECREASING TOWARD THE 25TH PERCENTILE OF THE
CLIMATOLOGICAL DISTRIBUTION. AS A RESULT, MORE FAVORABLE UPPER-LEVEL
DYNAMICS ARE EXPECTED TO ENHANCE THE POTENTIAL FOR SHOWERS AND
ISOLATED THUNDERSTORMS ACROSS THE FORECAST AREA. CONTINUE TO MONITOR
THE FORECAST FOR UPDATES.
WARM TO HOT CONDITIONS WILL PERSIST THROUGH MOST OF THE FORECAST
PERIOD, WITH AN ELEVATED HEAT RISK EXPECTED ACROSS COASTAL AND LOWER
ELEVATIONS OF THE ISLANDS. RESIDENTS AND VISITORS ARE ENCOURAGED TO
CONTINUE PRACTICING HEAT SAFETY MEASURES TO REDUCE THE RISK OF HEAT-
RELATED ILLNESSES.
AVIATION
(18Z TAFS)
ISSUED AT 1250 PM AST TUE JUL 21 2026
MOSTLY VFR CONDITIONS ACROSS MOST TAF SITES. A TROUGH WILL CONTINUE
TO AFFECT TJBQ, TIST, TISX AND TJPS WITH VCSH. WINDS WILL REMAIN
FROM THE E-NE THROUGH 21/23Z AND FROM 22/00Z ONWARDS WINDS WILL
GRADUALLY SHIFT FROM THE E-SE.
MARINE
ISSUED AT 1250 PM AST TUE JUL 21 2026
THE INDUCED SURFACE TROUGH WILL CONTINUE TO MOVE WEST OF THE
REGION TONIGHT WHILE ATLANTIC HIGH PRESSURE GRADUALLY REBUILDS. AS
A RESULT, WINDS WILL SHIFT FROM THE NORTHEAST TODAY TO THE EAST-
SOUTHEAST BY WEDNESDAY, INCREASING TO MODERATE TO LOCALLY FRESH
SPEEDS. SHOWERS AND THUNDERSTORMS WILL REMAIN POSSIBLE THROUGH
WEDNESDAY, WITH LOCALLY HIGHER WINDS AND SEAS NEAR STRONGER
CONVECTION. BY THURSDAY, A DRIER AIR MASS ACCOMPANIED BY MODERATE
CONCENTRATIONS OF SAHARAN DUST WILL OVERSPREAD THE REGION,
RESULTING IN HAZY SKIES AND REDUCED VISIBILITY. A TROPICAL WAVE
APPROACHING THE LESSER ANTILLES IS EXPECTED TO INCREASE MOISTURE
AND SHOWER ACTIVITY BY FRIDAY.
BEACH FORECAST
ISSUED AT 1250 PM AST TUE JUL 21 2026
A LOW RISK OF RIP CURRENTS WILL CONTINUE THROUGH WEDNESDAY.
HOWEVER, LIFE-THREATENING RIP CURRENTS CAN STILL OCCUR NEAR
GROINS, JETTIES, REEFS, AND PIERS. BEACHGOERS SHOULD ALWAYS SWIM
NEAR LIFEGUARDS, FOLLOW POSTED WARNING FLAGS, AND NEVER SWIM
ALONE.
SHOWERS AND THUNDERSTORMS WILL REMAIN POSSIBLE THROUGH WEDNESDAY.
PASSING SHOWERS WILL AFFECT WINDWARD BEACHES TONIGHT INTO
WEDNESDAY MORNING. AT THE SAME TIME, AFTERNOON THUNDERSTORMS ARE
EXPECTED TO DEVELOP MAINLY ACROSS NORTHERN PUERTO RICO ON
WEDNESDAY AS WINDS SHIFT TO THE EAST-SOUTHEAST. BEACHGOERS SHOULD
REMAIN WEATHER-AWARE, AS LIGHTNING CAN STRIKE FAR FROM RAINFALL.
IF THUNDER IS HEARD, LEAVE THE BEACH AND SEEK SHELTER IN A
SUBSTANTIAL BUILDING OR HARD-TOPPED VEHICLE.
AN ELEVATED RISK OF HEAT-RELATED ILLNESSES WILL CONTINUE ON
WEDNESDAY, ESPECIALLY FROM LATE MORNING THROUGH THE AFTERNOON
ACROSS URBAN AND COASTAL AREAS. STAY HYDRATED, SEEK SHADE WHENEVER
POSSIBLE, AND APPLY SUNSCREEN REGULARLY.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
MORNING SHIFT...CAM/MMC
EVENING SHIFT...MRR/YZR
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