685
FXCA62 TJSJ 230843
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
443 AM AST THU JUL 23 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 358 AM AST THU JUL 23 2026
* MODERATE SAHARAN DUST CONCENTRATIONS WILL LEAD TO HAZY SKIES,
REDUCED AIR QUALITY, AND LOWER VISIBILITY THROUGH THE END OF THE
WEEK.
* A WEAK TROPICAL WAVE IS EXPECTED TO BRING BRIEF SHOWERS ON
FRIDAY, WHILE ANOTHER ONE COULD BRING MORE SHOWERS FROM LATE
SUNDAY INTO EARLY NEXT WEEK.
* WARM TO HOT CONDITIONS ARE EXPECTED FOR THE NEXT FEW DAYS WITH
DAILY MAX TEMPS REACHING THE LOW 90S ACROSS THE LOWER ELEVATIONS
OF THE ISLANDS.
SHORT TERM(TODAY THROUGH SATURDAY)
ISSUED AT 358 AM AST THU JUL 23 2026
A DENSE SAHARAN AIR LAYER (SAL) WILL GRADUALLY FILTER OVER THE
REGION THROUGH THE REST OF THE SHORT-TERM PERIOD. COLUMN MOISTURE
IS EXPECTED TO DECREASE, WITH MODEL GUIDANCE SUGGESTING A SHARP
DROP IN PRECIPITABLE WATER (PWAT) TO NEAR 1.20 BY THIS EVENING.
HOWEVER, A LINGERING UPPER-LEVEL TROUGH TO OUR NORTHEAST WILL
CONTINUE TO PROVIDE SOME INSTABILITY, AND ISOLATED THUNDERSTORMS
COULD STILL DEVELOP BETWEEN THE WATERS OF THE ISLANDS AND THE
ATLANTIC WATERS THIS MORNING. OVER LAND AREAS, RAIN CHANCES SHOULD
BE CONFINED TO BRIEF, ISOLATED AFTERNOON THUNDERSTORMS AND SHOWERS
OVER WESTERN PUERTO RICO DRIVEN BY DIURNAL AND LOCAL EFFECTS.
ELSEWHERE, CONVECTIVE ACTIVITY IS EXPECTED TO BE SUPPRESSED AS THE
SAL LAYER BRINGS MODERATE CONCENTRATIONS OF DUST, MID-LEVEL
DRYING (700–500 MB RH DECREASING FROM 50 TO 30%), AND A CAPPING
INVERSION LAYER. REDUCED AIR QUALITY AND HAZY SKIES, ALONGSIDE
MAXIMUM TEMPERATURES REACHING THE LOW 90S ACROSS THE LOWER
ELEVATIONS OF THE ISLANDS ARE EXPECTED TODAY.
MOISTURE WILL RECOVER SLIGHTLY ON FRIDAY MORNING AS A WEAK
TROPICAL WAVE MOVES ACROSS THE REGION AND LOW-TO-MID LEVEL
RELATIVE HUMIDITY RECOVERS TO SEASONAL VALUES. GUIDANCE SUGGESTS
PWAT VALUES WILL SURGE BACK TOWARD 1.80 TO 2.00 INCHES BY LATE
FRIDAY MORNING, HELPING ERODE THE LOW-TO-MID LEVEL CAP. THIS WEAK
WAVE WILL BRING A TYPICAL SEASONAL CONVECTIVE PATTERN, BEGINNING
WITH PASSING MORNING TRADE WIND SHOWERS ACROSS THE U.S. VIRGIN
ISLANDS AND EASTERN PUERTO RICO, FOLLOWED BY SCATTERED AFTERNOON
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE INTERIOR AND WESTERN
PUERTO RICO. HEAVY DOWNPOURS FROM LOCALIZED AFTERNOON CONVECTION
ON FRIDAY MAY PRODUCE PONDING OF WATER ON ROADWAYS AND MINOR URBAN
AND SMALL STREAM FLOODING. HEAT INDICES WILL REMAIN ELEVATED IN
THE LOW 100S ACROSS COASTAL URBAN AREAS.
BY SATURDAY, THE LINGERING SAL WITH LOWER DUST CONCENTRATIONS WILL
CAUSE PWAT TO DROP SLIGHTLY AROUND 1.60 TO 1.75 INCHES AS THE
DRIER 700–500 MB LAYER RETURNS. HOWEVER, THE UPPER-LEVEL TROUGH
POSITIONING OVER THE NORTHEASTERN CARIBBEAN WILL MAINTAIN
MARGINALLY COOLER MID-LEVEL TEMPERATURES (-7°C TO -8°C AT 500 MB),
SUPPLYING ENOUGH UPPER-LEVEL INSTABILITY TO SUPPORT LOCALIZED
AFTERNOON CONVECTION DESPITE MODEST MID-LEVEL MOISTURE. WIND FLOW
WILL STEER PASSING SHOWERS ACROSS WINDWARD AREAS DURING THE
OVERNIGHT AND EARLY MORNING HOURS, FOLLOWED BY ISOLATED TO
SCATTERED AFTERNOON SHOWER AND THUNDERSTORM DEVELOPMENT FROM THE
INTERIOR TO WESTERN PR. THE FLOOD RISK ACROSS THESE AREAS WILL
REMAIN LOCALIZED.
LONG TERM(SUNDAY THROUGH THURSDAY)
ISSUED AT 358 AM 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
(06Z TAFS)
ISSUED AT 358 AM AST THU JUL 23 2026
MAINLY VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS ALL TERMINALS
DURING THE NEXT 24 HOURS. HOWEVER, EARLY MORNING SHOWERS COULD
LEAD TO BRIEF MVFR CONDS AT TIST/TJSJ, AND FM 23/16-22Z LOCALLY
INDUCED SHRA/TSRA EXPECTED TO DEVELOP IN AND AROUND TJBQ, CAUSING
TEMPO MVFR TO BRIEF IFR. HZ WILL INCREASE GRADUALLY THROUGH THE
DAY, AND VSBY MAY DROP TO NEAR 6SM. LOW-LEVEL WINDS WILL CONTINUE
ESE AT 9-15 KT WITH SEA BREEZE VARIATIONS AND HIGHER GUSTS AFT
23/14Z.
MARINE
ISSUED AT 358 AM AST THU JUL 23 2026
ATLANTIC HIGH PRESSURE WILL MAINTAIN MODERATE TO LOCALLY FRESH WINDS
INTO THE WEEKEND, GENERALLY FROM THE EAST BUT WITH VARIATIONS IN
DIRECTION AT TIMES. CHOPPY SEAS ARE EXPECTED, AND SMALL CRAFT
OPERATORS SHOULD EXERCISE CAUTION. MODERATE CONCENTRATIONS OF
SAHARAN DUST WILL PROMOTE HAZY CONDITIONS AND REDUCED VISIBILITY
OVER THE NEXT FEW DAYS. LINGERING SHOWERS AND THUNDERSTORMS WILL
REMAIN POSSIBLE OVER PORTIONS OF THE LOCAL WATERS TODAY. WEAK
TROPICAL WAVES ARE EXPECTED TO APPROACH THE REGION ON FRIDAY AND LATE
THIS WEEKEND INTO EARLY NEXT WEEK, BRINGING AN INCREASE IN SHOWER
ACTIVITY.
BEACH FORECAST
ISSUED AT 358 AM AST THU JUL 23 2026
A MODERATE RISK OF RIP CURRENTS WILL CONTINUE INTO THE WEEKEND FOR
BEACHES ALONG THE NORTH AND EAST COASTS OF PUERTO RICO, INCLUDING
VIEQUES AND CULEBRA, AS WELL AS THE U.S. VIRGIN ISLANDS. LIFE-
THREATENING RIP CURRENTS ARE POSSIBLE, AND BEACHGOERS SHOULD
EXERCISE CAUTION AND SWIM NEAR A LIFEGUARD WHENEVER POSSIBLE. HOT
AND HUMID CONDITIONS WILL ALSO POSE A RISK OF HEAT-RELATED ILLNESS,
ESPECIALLY FOR THOSE SPENDING EXTENDED PERIODS OUTDOORS. HAZY
CONDITIONS ARE EXPECTED OVER THE NEXT FEW DAYS DUE TO SAHARAN DUST.
ISOLATED THUNDERSTORMS MAY ALSO DEVELOP AT TIMES, POSING A RISK OF
LIGHTNING AT AREA BEACHES.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
AVIATION/SHORT TERM...DSR
LONG TERM...YZR
BEACH/MARINE...ICP
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