115
FXCA62 TJSJ 231845
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
245 PM AST THU JUL 23 2026
...NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER...
KEY MESSAGES
UPDATED AT 241 PM AST THU JUL 23 2026
* A HEAT ADVISORY REMAINS IN EFFECT ACROSS ALL COASTAL AREAS OF
PUERTO RICO, CULEBRA, AND VIEQUES, INCLUDING THE VICINITY OF
CAGUAS AND THE U.S. VIRGIN ISLANDS.
* A WEAK TROPICAL WAVE WILL MOVE ACROSS THE ISLANDS BY TOMORROW
MORNING, INCREASING THE FREQUENCY OF SHOWER ACTIVITY IN SOME
AREAS.
* A MORE VIGOROUS TROPICAL WAVE IS FORECAST FROM LATE SUNDAY INTO
MONDAY, INCREASING THE POTENTIAL FOR SHOWERS AND FLOODING ON
MONDAY.
* THERE IS A MODERATE RISK OF RIP CURRENTS ACROSS LOCALLY
EXPOSED BEACHES FOR THE REST OF THE WORKWEEK INTO THE WEEKEND.
SHORT TERM(THIS EVENING THROUGH SATURDAY)
ISSUED AT 241 PM AST THU JUL 23 2026
A SAHARAN AIR LAYER (SAL) WILL REMAIN THE DOMINANT WEATHER FEATURE
THROUGH THE SHORT-TERM PERIOD. THE ASSOCIATED DRY AIR INTRUSION WILL
CONTINUE STRENGTHENING TONIGHT, WITH PRECIPITABLE WATER VALUES
FALLING TO AROUND 1.0 INCH, NEARLY TWO STANDARD DEVIATIONS BELOW
NORMAL, WHILE PRONOUNCED DRYING BETWEEN 700 AND 500 MB LIMITS CLOUD
DEVELOPMENT AND RAINFALL POTENTIAL. ALTHOUGH A LINGERING UPPER-LEVEL
TROUGH WILL MAINTAIN MODEST INSTABILITY ALOFT, CURRENT RADAR TRENDS
INDICATE THAT SHOWERS HAVE STRUGGLED TO PERSIST AS THEY ENCOUNTER
THE INCREASINGLY DRY ENVIRONMENT. THEREFORE, ONLY ISOLATED AFTERNOON
CONVECTION IS EXPECTED ACROSS PORTIONS OF NORTHWESTERN PUERTO RICO
BEFORE ACTIVITY QUICKLY DIMINISHES THIS EVENING. HAZY SKIES, REDUCED
AIR QUALITY, AND ABOVE-NORMAL TEMPERATURES WILL CONTINUE ACROSS THE
ISLANDS, SUPPORTING ELEVATED HEAT INDICES IN THE LOWER ELEVATIONS.
ON FRIDAY, A WEAK TROPICAL WAVE WILL BRIEFLY INCREASE LOW-LEVEL
MOISTURE, ALLOWING PRECIPITABLE WATER VALUES TO RECOVER TO NEAR
SEASONAL LEVELS AND SUPPORTING A MORE TYPICAL PATTERN OF PASSING
MORNING SHOWERS FOLLOWED BY SCATTERED AFTERNOON CONVECTION ACROSS
THE INTERIOR AND WESTERN PORTIONS OF PUERTO RICO. HOWEVER, THE
MOISTURE INCREASE IS EXPECTED TO BE SHORT-LIVED, AS THE SURROUNDING
SAL AIRMASS REMAINS IN PLACE. WHILE LOCALLY HEAVY DOWNPOURS CANNOT
BE RULED OUT GIVEN THE PERSISTENT UPPER-LEVEL TROUGH AND COOLER
TEMPERATURES ALOFT, WIDESPREAD OR LONG-DURATION RAINFALL IS NOT
ANTICIPATED.
BY FRIDAY EVENING INTO SATURDAY, SAHARAN DUST CONCENTRATIONS ARE
FORECAST TO INCREASE ONCE AGAIN TO MODERATE LEVELS AS THE TRANSIENT
MOISTURE PLUME EXITS THE REGION. ALTHOUGH MOISTURE SHOULD REMAIN
NEAR CLIMATOLOGICAL VALUES, THE RETURN OF DRIER MID-LEVEL AIR WILL
ONCE AGAIN LIMIT CONVECTIVE COVERAGE, RESULTING IN A MORE LOCALIZED
PATTERN OF AFTERNOON SHOWERS AND ISOLATED THUNDERSTORMS OVER WESTERN
PUERTO RICO. HAZY SKIES AND WARM TEMPERATURES WILL PERSIST THROUGH
THE REMAINDER OF THE SHORT-TERM PERIOD.
LONG TERM(SUNDAY THROUGH NEXT WEDNESDAY)
ISSUED AT 241 PM AST THU JUL 23 2026
CURRENT MODEL GUIDANCE SUGGESTS AN EVOLVING WETTER PATTERN TO BEGIN
THE LONG-TERM PERIOD. A TROPICAL WAVE-DRIVEN MOISTURE SURGE WILL
AFFECT THE REGION, WITH PWAT VALUES FOLLOWING AN INCREASING TREND TO
ABOVE-NORMAL LEVELS FROM SUNDAY THROUGH EARLY WEDNESDAY. ALOFT, AN
UPPER-LEVEL LOW POSITIONED OVER THE ISLANDS THROUGH MONDAY WILL
MAINTAIN LOWER 250 MB HEIGHTS AND COOLER 500 MB TEMPERATURES, WITH
BOTH REMAINING NEAR OR BELOW SEASONAL NORMS. MOISTURE WILL ALSO
INCREASE IN THE MID AND UPPER LEVELS, CREATING A MORE UNSTABLE
PATTERN ACROSS THE ISLANDS. AS A RESULT, SUNDAY AND MONDAY ARE
EXPECTED TO HAVE THE MOST FAVORABLE DYNAMICS FOR THE DEVELOPMENT OF
SHOWERS AND THUNDERSTORMS. ADDITIONALLY, WINDS ARE FORECAST TO
REMAIN VERY LIGHT ON THOSE DAYS, RESULTING IN SLOW-MOVING SHOWERS
AND THUNDERSTORMS WITH THE POTENTIAL FOR HIGHER RAINFALL
ACCUMULATIONS.
BY TUESDAY AND WEDNESDAY, THE UPPER-LEVEL LOW WILL SHIFT SLIGHTLY
WEST OF THE AREA, ALLOWING FOR INCREASING STABILITY ALOFT, AS
REFLECTED BY RISING HEIGHTS. AS ATLANTIC HIGH PRESSURE GRADUALLY
STRENGTHENS, EASTERLY WINDS ARE EXPECTED TO INCREASE, BECOMING
BREEZY TO LOCALLY WINDY. HOWEVER, MOISTURE CONTENT WILL REMAIN ABOVE
AVERAGE AND, WHEN COMBINED WITH LOCAL EFFECTS AND DIURNAL HEATING,
WILL LIKELY RESULT IN WINDWARD SHOWERS DURING THE NIGHT AND MORNING,
FOLLOWED BY AFTERNOON CONVECTION ACROSS THE INTERIOR AND WESTERN
PORTIONS OF PUERTO RICO.
THE FLOOD THREAT REMAINS ELEVATED ON SUNDAY, WITH THE POTENTIAL FOR
FLOODING IN URBAN AREAS, ROADS, SMALL STREAMS, AND WASHES. FROM
MONDAY THROUGH TUESDAY, THE FLOOD THREAT IS CURRENTLY LIMITED, WITH
PONDING OF WATER ON ROADS AND IN POORLY DRAINED AREAS BEING THE
PRIMARY CONCERN. THIS FORECAST WILL BE REFINED WITH EACH UPDATE AS
CONFIDENCE CONTINUES TO INCREASE.
DRIER AIR WILL BEGIN FILTERING INTO THE AREA WEDNESDAY NIGHT THROUGH
THURSDAY, ACCOMPANIED BY PROBABLY SOME SAHARAN DUST. AS PWAT VALUES
DECREASE TO NEAR SEASONAL LEVELS, ISOLATED TRADE WIND SHOWERS WILL
CONTINUE, BUT SHOWER COVERAGE IS EXPECTED TO BE MORE LIMITED THAN
DURING THE PREVIOUS DAYS. THROUGHOUT MOST OF THE FORECAST PERIOD,
WARM TO HOT CONDITIONS WILL PERSIST, BRINGING A LIMITED TO ELEVATED
HEAT RISK ACROSS COASTAL AND URBAN AREAS OF THE ISLANDS.
AVIATION
(18Z TAFS)
ISSUED AT 241 PM AST THU JUL 23 2026
MAINLY VFR CONDS WILL PREVAIL AT ALL TAF SITES THROUGH THE FCST
PERIOD. LIMITED SHRA/TSRA DEVELOPMENT IS EXPECTED THIS AFTN DUE TO
DRY AIR ASSOCIATED WITH A SAL, ALTHOUGH BRIEF MVFR/MTN OBSC CANNOT
BE RULED OUT NEAR TJBQ. HZ WILL PERSIST ACROSS THE LOCAL ISLANDS.
SFC WINDS ESE 10-15 KT WITH HIGHER GUSTS AND SEA BREEZE VARIATIONS
THROUGH EARLY EVENING, BECOMING LIGHTER OVERNIGHT AND INCREASING
AGAIN AFT 24/13Z.
MARINE
ISSUED AT 241 PM AST THU JUL 23 2026
NO CHANGES WERE MADE TO THE MARINE FORECAST. AT THE SURFACE, BROAD
HIGH PRESSURE WILL MAINTAIN MODERATE TO LOCALLY FRESH WINDS FOR
THE REST OF THE DAY INTO SATURDAY. WINDS WILL REMAIN FROM THE
EAST-SOUTHEAST TODAY, BECOMING MORE EASTERLY BY SATURDAY. SAHARAN
DUST PARTICLES WILL REMAIN IN PLACE, SLIGHTLY LIMITING VISIBILITY
BUT NOT AFFECTING MARINE OPERATIONS. A WEAK TROPICAL WAVE IS
FORECAST TO MOVE ACROSS THE REGION ON FRIDAY, BUT WIDESPREAD
SHOWER ACTIVITY IS NOT ANTICIPATED. A MORE VIGOROUS TROPICAL WAVE
IS EXPECTED FROM LATE SUNDAY INTO MONDAY, INCREASING AVAILABLE
MOISTURE AND THUNDERSTORM ACTIVITY OVER THE LOCAL CARIBBEAN
WATERS, WHICH WILL RESULT IN LOCALIZED HAZARDOUS MARINE
CONDITIONS.
BEACH FORECAST
ISSUED AT 241 PM AST THU JUL 23 2026
THERE IS A LOW TO MODERATE RISK OF RIP CURRENTS ACROSS ALL LOCALLY
EXPOSED BEACHES OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS. LIFE-
THREATENING RIP CURRENTS ARE POSSIBLE, AND BEACHGOERS SHOULD
EXERCISE CAUTION AND SWIM NEAR A LIFEGUARD WHENEVER POSSIBLE. HAZY
CONDITIONS ARE EXPECTED INTO FRIDAY DUE TO SAHARAN DUST. ISOLATED
THUNDERSTORMS MAY ALSO DEVELOP AT TIMES, POSING A LIGHTNING RISK
AT AREA BEACHES. THIS ACTIVITY IS ASSOCIATED WITH A WEAK TROPICAL
WAVE MOVING ACROSS THE AREA TOMORROW, FOLLOWED BY A MORE VIGOROUS
TROPICAL WAVE EXPECTED SUNDAY INTO MONDAY.
FIRE WEATHER
ISSUED AT 241 PM AST THU JUL 23 2026
AN INTERESTING PATTERN IS FORECAST FOR TOMORROW'S FIRE DANGER
THREAT. A MUCH DRIER AIRMASS WILL DOMINATE THE REGION BY EARLY
MORNING; HOWEVER, THE ARRIVAL OF A WEAK TROPICAL WAVE WILL QUICKLY
INCREASE RELATIVE HUMIDITY (RH) ACROSS THE AREA. MEANWHILE,
SURFACE WINDS WILL REMAIN BELOW THRESHOLD VALUES, MOSTLY RANGING
BETWEEN 10-15 MPH. GIVEN THE EXPECTED CONDITIONS, THERE WILL BE A
MODERATE FIRE DANGER RISK DURING THE DAY.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY UNTIL 5 PM AST THIS AFTERNOON FOR PRZ001>005-007-
008-010>013.
VI...HEAT ADVISORY UNTIL 5 PM AST THIS AFTERNOON FOR VIZ001-002.
AM...NONE.
SHORT TERM & AVIATION...CVB
LONG TERM....YZR
MARINE, BEACH FORECAST & FIRE WEATHER...LIS
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