334
FXCA62 TJSJ 220810
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
410 AM AST WED JUL 22 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 357 AM AST WED JUL 22 2026
* ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS ARE EXPECTED TODAY
ACROSS THE ISLANDS. BRIEF GUSTY WINDS AND AN ELEVATED FLOOD
THREAT CAN BE EXPECTED WITH THIS ACTIVITY.
* HOT TEMPERATURES WITH INCREASED HEAT RISKS ARE EXPECTED TODAY
AND ON THURSDAY ALONG THE URBAN AND LOWER ELEVATIONS OF THE
ISLANDS.
* POOR AIR QUALITY AND HAZY SKIES ARE EXPECTED TO RETURN LATE
THIS WEEK AS MODERATE SAHARAN DUST CONCENTRATIONS MOVE INTO THE
REGION.
SHORT TERM(TODAY THROUGH FRIDAY)
ISSUED AT 357 AM AST WED JUL 22 2026
AN ACTIVE WEATHER PATTERN WILL UNFOLD ACROSS THE LOCAL REGION
TODAY, DRIVEN BY AN UPPER-LEVEL TROUGH AND AN INDUCED SURFACE
TROUGH TO OUR NORTH THAT CONTINUES TO PULL A SURGE OF TROPICAL
MOISTURE OVER THE AREA. PRECIPITABLE WATER (PWAT) VALUES WILL
RANGE BETWEEN 1.80 AND 2.00 INCHES, SUPPORTING SCATTERED
CONVECTIVE DEVELOPMENT. STRONG DAYTIME HEATING, SEA BREEZE
CONVERGENCE, AND DYNAMIC UPPER-LEVEL DIVERGENCE WILL TRIGGER
AFTERNOON SHOWERS AND THUNDERSTORMS, PRIMARILY OVER THE INTERIOR
AND WEST/NORTHWEST PUERTO RICO. HEAVY DOWNPOURS WILL PRESENT A
LOCALIZED URBAN AND SMALL STREAM FLOODING RISK. PASSING SHOWERS
WILL CONTINUE TO AFFECT THE U.S. VIRGIN ISLANDS AND EASTERN
COASTAL AREAS THROUGH MIDDAY, WITH A SLIGHT CHANCE FOR
THUNDERSTORM DEVELOPMENT.
IN ADDITION TO THE RAINFALL RISK, HOT AND HUMID CONDITIONS WILL
PREVAIL TODAY AND EARLY THURSDAY. THE COMBINATION OF WARM 925 MB
TEMPERATURES NEAR 23C AND LIGHT TO MODERATE SOUTHEASTERLY WIND
FLOW WILL LIMIT LOW-LEVEL COOLING, CAUSING HEAT INDICES TO REACH
OR EXCEED 108F TO 111F ACROSS THE LOWER ELEVATIONS AND URBAN AREAS
OF THE ISLANDS, MAKING HEAT ADVISORIES LIKELY BOTH TODAY AND
THURSDAY. FROM LATE TONIGHT INTO THURSDAY, A DENSE SAHARAN AIR
LAYER (SAL) WILL ENGULF THE NORTHEASTERN CARIBBEAN, BRINGING A
SHARP REDUCTION IN MOISTURE CONTENT (PWAT DROPPING TO NEAR 1.25
INCHES), STRONG MID-LEVEL CAP, AND HAZY SKIES. THIS HOSTILE AIR
MASS WILL RESTRICT THURSDAY'S CONVECTIVE ACTIVITY TO BRIEF,
ISOLATED AFTERNOON SHOWERS IN WESTERN PUERTO RICO WHILE DEGRADING
AIR QUALITY.
THE SAHARAN DUST PLUME WILL RETREAT WESTWARD BY FRIDAY AS ANOTHER
SURGE OF TROPICAL MOISTURE FROM A WEAK TROPICAL WAVE PUSHES INTO
THE LOCAL AREA. PRECIPITABLE WATER LEVELS WILL BRIEFLY RECOVER TO
NEAR 2.00 INCHES ALONGSIDE ERODING THE MID-LEVEL CAP. THIS RAPID
MOISTURE RETURN WILL RE-ESTABLISH A TYPICAL SEASONAL CONVECTIVE
SETUP, BRINGING PASSING MORNING SHOWERS TO THE U.S. VIRGIN ISLANDS
AND EASTERN PUERTO RICO, FOLLOWED BY SCATTERED AFTERNOON SHOWERS
AND THUNDERSTORMS FOCUSED ACROSS THE INTERIOR AND WESTERN PUERTO
RICO.
LONG TERM(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 357 AM AST WED JUL 22 2026
A SURFACE HIGH PRESSURE OVER THE ATLANTIC WILL GENERALLY DOMINATE
DURING THE PERIOD WITH LOWS STAYING MAINLY OVER THE WESTERN TO
NORTHERN ATLANTIC, THIS WILL PROMOTE BREEZY EASTERLY FLOW ON
SATURDAY AND EAST-SOUTHEASTERLY FLOW LATE SUNDAY ONWARDS, WITH
BREEZY CONDITIONS PERSISTING AT LEAST THROUGH THE WEEKEND.
HOWEVER, MOST AVAILABLE MOISTURE WILL REMAIN BELOW 800 MB THROUGH
SUNDAY AFTERNOON WITH PRECIPITABLE WATER (PWAT) VALUES STAYING
BELOW NORMAL TO NORMAL RANGE, WITH ABOVE NORMAL VALUES POSSIBLE
DURING AFTERNOON CONVECTION. TEMPERATURES AT 500 MB WILL REMAIN
AROUND -7 TO -8 °C, AT NORMAL TO BELOW NORMAL, AND WILL SUPPORT
ISOLATED T-STORMS ASSOCIATED WITH AFTERNOON CONVECTION (DUE TO
DIURNAL HEATING, SEA BREEZE CONVERGENCE AND LOCAL EFFECTS).
SHOWERS WILL ALSO BE STEERED TOWARDS THE ISLANDS FROM TIME TO TIME
ESPECIALLY DURING THE MORNING AND NIGHT HOURS, HOWEVER A LIMITED
FLOODING RISK CAN OCCUR MAINLY DURING AFTERNOON CONVECTION OVER
INTERIOR TO W AND NW PUERTO RICO.
LOOKING AHEAD FROM LATE SUNDAY INTO WEDNESDAY, RECENT MODEL GUIDANCE
INDICATES A TROPICAL WAVE-DRIVEN MOISTURE SURGE WILL AFFECT THE
REGION, WITH PWAT LEVELS TO NORMAL AND ABOVE-NORMAL THRESHOLDS.
FURTHERMORE, AN UPPER-LEVEL LOW POSITIONED OVER THE ISLANDS FROM
SATURDAY THROUGH MONDAY WILL MAINTAIN LOWER 250 MB HEIGHTS AND
COOLER 500 MB TEMPERATURES WITH BOTH TRENDING NEAR OR BELOW SEASONAL
NORMS. AVAILABLE MOISTURE WILL IN TURN REACH THE MID TO UPPER LEVELS
THROUGH AT LEAST EARLY WEDNESDAY. THESE FACTORS COMBINED WILL FOSTER
MORE FAVORABLE UPPER-LEVEL DYNAMICS, INCREASING THE LIKELIHOOD OF
SHOWER ACTIVITY AND ISOLATED THUNDERSTORM DEVELOPMENT ACROSS THE
FORECAST AREA. DRIER AIR WILL START TO FILTER OVER THE AREA
WEDNESDAY NIGHT.
MODERATE TO LOCALLY HIGH CONCENTRATIONS OF SAHARAN DUST WILL
CONTINUE TO FILTER OVER THE ISLANDS THROUGH MOST OF THE WEEKEND WITH
CONCENTRATIONS DECREASING TO LOW (WITH ISOLATED PATCHES OF MODERATE
CONCENTRATIONS FROM TIME TO TIME) LATE SUNDAY THROUGH TUESDAY.
CURRENT GUIDANCE SUGGESTS THAT MODERATE TO HIGH CONCENTRATIONS OF
SAHARAN DUST WILL THEN RETURN BY WEDNESDAY.
THROUGHOUT THE MAJORITY OF THE FORECAST PERIOD, WARM TO HOT
CONDITIONS WILL PERSIST, BRINGING A LIMITED TO ELEVATED RISK OF HEAT
TO COASTAL, URBAN AND LOWER ELEVATIONS. TO MITIGATE THE DANGER OF
HEAT-RELATED ILLNESSES, BOTH VISITORS AND RESIDENTS ARE ADVISED TO
KEEP FOLLOWING HEAT SAFETY GUIDELINES.
AVIATION
(06Z TAFS)
ISSUED AT 357 AM AST WED JUL 22 2026
SHRA/TSRA WILL CONTINUE ACROSS THE LOCAL AREA TODAY DUE TO A SFC
TROUGH. THIS MAY LEAD TO TEMPO MVFR CONDS ACROSS THE USVI AND
EASTERN PR TERMINALS THROUGH THE MORNING HOURS, AND AT TJSJ TILL
EARLY THIS AFTERNOON. AT TJBQ, MVFR TO IFR CONDS ARE LIKELY BTW
22/17-22Z. LOW-LEVEL WINDS ESE AT 9-14 KT WITH STRONGER GUSTS AT
TIMES AND WITH A NORTHERLY COMPONENT IN SEA BREEZE VARIATIONS
ALONG THE NORTH AND WEST COAST OF PR.
MARINE
ISSUED AT 357 AM AST WED JUL 22 2026
AN INDUCED SURFACE TROUGH WILL CONTINUE MOVING WEST ACROSS THE
LOCAL WATERS TODAY WHILE ATLANTIC HIGH PRESSURE GRADUALLY
REBUILDS. EAST TO SOUTHEAST WINDS WILL GRADUALLY BECOME
ESTABLISHED THROUGH THE DAY, AROUND MODERATE TO LOCALLY FRESH
SPEEDS. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL PERSIST
ACROSS THE LOCAL WATERS, WITH LOCALLY HIGHER WINDS AND SEAS
POSSIBLE IN AND NEAR STRONGER CONVECTION. BY THURSDAY, A DRIER AIR
MASS ACCOMPANIED BY MODERATE CONCENTRATIONS OF SAHARAN DUST WILL
OVERSPREAD THE REGION, RESULTING IN HAZY CONDITIONS AND REDUCED
VISIBILITY. A TROPICAL WAVE APPROACHING THE LESSER ANTILLES WILL
INCREASE MOISTURE ACROSS THE LOCAL WATERS BY FRIDAY, LEADING TO
INCREASING SHOWER ACTIVITY AND STRENGTHENING EAST WINDS.
BEACH FORECAST
ISSUED AT 357 AM AST WED JUL 22 2026
A LOW RISK OF RIP CURRENTS WILL PERSIST TODAY ACROSS THE LOCAL
BEACHES. HOWEVER, LIFE-THREATENING RIP CURRENTS CAN STILL OCCUR,
ESPECIALLY NEAR GROINS, JETTIES, REEFS, AND PIERS. BEACHGOERS SHOULD
CONTINUE TO EXERCISE CAUTION WHEN ENTERING THE WATER. A MODERATE
RISK OF RIP CURRENTS IS ANTICIPATED BY THURSDAY INTO THE WEEKEND
ALONG THE NORTHERN AND EASTERN BEACHES OF PUERTO RICO, VIEQUES,
CULEBRA, AND THE U.S. VIRGIN ISLANDS. UNDER A MODERATE RISK, LIFE-
THREATENING RIP CURRENTS ARE POSSIBLE, BEACHGOERS ARE URGED TO
EXERCISE CAUTION.
AS A SURFACE TROUGH CONTINUES MOVING ACROSS THE REGION TODAY,
SHOWERS AND THUNDERSTORMS WILL REMAIN POSSIBLE. IF THUNDER IS HEARD,
SEEK SHELTER IMMEDIATELY INSIDE OF A BUILDING. ANOTHER BEACH HAZARD
TODAY WILL BE THE HEAT. AN ELEVATED HEAT RISK IS EXPECTED ALONG
COASTAL AREAS OF THE ISLANDS. STAY HYDRATED BY DRINKING PLENTY OF
WATER.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY FROM 10 AM THIS MORNING TO 4 PM AST THIS AFTERNOON
FOR PRZ001>005-007-008-010>013.
VI...HEAT ADVISORY FROM 10 AM THIS MORNING TO 4 PM AST THIS AFTERNOON
FOR VIZ001-002.
AM...NONE.
SHORT TERM/AVIATION...DSR
LONG TERM/BEACH/MARINE...MRR
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