496
FXCA62 TJSJ 180703
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
303 AM AST THU JUN 18 2026
...NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER...
KEY MESSAGES
ISSUED AT 303 AM AST THU JUN 18 2026
* PERIODS OF MODERATE TO HEAVY RAINFALL, WITH ISOLATED
THUNDERSTORMS, MAY RESULT IN PONDING OF WATER ON ROADS AND
POORLY DRAINED AREAS, URBAN AND SMALL-STREAM FLOODING, AND
ISOLATED FLASH FLOODING TODAY, WITH THE GREATEST IMPACTS
EXPECTED FROM LATE MORNING THROUGH THE AFTERNOON, PARTICULARLY
ACROSS PUERTO RICO.
* DANGEROUS HEAT INDEX VALUES ARE EXPECTED EACH AFTERNOON AS HOT
TEMPERATURES COMBINE WITH THE AVAILABLE MOISTURE, INCREASING THE
RISK OF HEAT EXHAUSTION AND HEAT STROKE, ESPECIALLY IN COASTAL
AND URBAN AREAS, POORLY VENTILATED LOCATIONS, AND AMONG
VULNERABLE POPULATIONS.
* MODERATE TO HIGH CONCENTRATIONS OF SAHARAN DUST WILL SPREAD
ACROSS PUERTO RICO AND THE U.S. VIRGIN ISLANDS FROM EARLY FRIDAY
THROUGH AT LEAST LATE SATURDAY NIGHT, REDUCING AIR QUALITY AND
VISIBILITY WHILE POTENTIALLY AGGRAVATING RESPIRATORY CONDITIONS
AMONG SENSITIVE GROUPS.
* A TROPICAL WAVE WILL MOVE ACROSS THE REGION ON SUNDAY,
INCREASING THE RISK OF HEAVY RAINFALL, THUNDERSTORMS, URBAN AND
SMALL- STREAM FLOODING, AND ISOLATED FLASH FLOODING ACROSS
PORTIONS OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS.
* LIFE-THREATENING RIP CURRENTS WILL REMAIN POSSIBLE ALONG
EXPOSED BEACHES OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS
THROUGHOUT THE FORECAST PERIOD. BEACHGOERS SHOULD EXERCISE
CAUTION AND FOLLOW LOCAL BEACH SAFETY GUIDANCE.
SHORT TERM(TODAY THROUGH SATURDAY)
ISSUED AT 303 AM AST THU JUN 18 2026
MOST OF THE ISLANDS OBSERVED QUIET WEATHER CONDITIONS AMID
WARMER-THAN-NORMAL LOW TEMPERATURES. HOWEVER, SOME SHOWERS
ASSOCIATED WITH AN APPROACHING WEAK TROPICAL WAVE WERE NOTED
MOVING ACROSS THE EASTERN THIRD OF PR AND THE SOUTHERN US VIRGIN
ISLANDS OVERNIGHT. WINDS WERE MAINLY FROM THE EAST TO EAST-
SOUTHEAST AT 10 MPH OR LESS UNDER THE INFLUENCE OF LAND BREEZE
FLUCTUATIONS.
ALTHOUGH THE WESTERN AND NORTHERN SECTIONS OF PR, AS WELL AS THE
USVI, WILL OBSERVE PERIODS OF NO RAIN AMID A WARMER-THAN-NORMAL
MORNING, THE ARRIVAL OF A WEAK TROPICAL WAVE WILL INCREASE THE
CHANCE FOR SHOWERS AND ISOLATED THUNDERSTORMS, ESPECIALLY FROM
MID-MORNING ONWARD. IN TERMS OF MID AND UPPER-LEVEL DYNAMICS, THIS
WAVE WILL ENCOUNTER A HOSTILE ENVIRONMENT AS A DRY AIR MASS IS
OBSERVED AT THOSE LEVELS, WHICH COULD LIMIT THE POTENTIAL TO
OBSERVE WIDESPREAD ACTIVITY. HOWEVER, SOME GUIDANCE INDICATES THE
POTENTIAL TO OBSERVE LOW AND MID-LEVEL VORTICITY ASSOCIATED WITH
THIS WAVE, WHICH, COMBINED WITH LOCAL EFFECTS, LOW-LEVEL
CONVERGENCE, TOPOGRAPHY, AND EXCESSIVE HEATING, COULD ENHANCE THE
ACTIVITY. FOR THAT REASON, OUR FORECAST CALLS FOR THE BEST CHANCE
OF FLOODING RAINS DOWNWIND FROM EL YUNQUE INTO THE SAN JUAN
METROPOLITAN AREA, AS WELL AS ALONG THE CORDILLERA CENTRAL AND THE
NORTHWEST QUADRANT. REGARDLESS, THE USVI AND ADDITIONAL PARTS OF
PR SHOULD MONITOR THE EVOLUTION OF WEATHER CONDITIONS, AS THERE IS
A CHANCE OF RAIN AND THUNDERSTORMS.
ON THE OTHER HAND, TEMPERATURES WISE, THE COMBINATION OF THE
AVAILABLE MOISTURE, WITH THE WARMER THAN NORMAL LOW TEMPERATURES
WHICH WILL ENHANCE THE POTENTIAL TO REACH THE 90S ALONG THE
COASTAL AREAS DURING THE MAXIMUM DIURNAL HEATING TODAY IN THE
AREAS WITHOUT RAIN WILL RESULT IN HEAT INDICES RANGING FROM THE
UPPER 90S TO THE 110 DEGREES FAHRENHEIT, ESPECIALLY ACROSS THE
URBAN AND COASTAL AREAS OF THE USVI AND PR. THIS TREND WILL EXTEND
INTO THE SHORT TERM.
TRAILING TODAY'S TROPICAL WAVE, A LARGE SAHARAN AIR LAYER (SAL)
WILL MOVE ACROSS THE REGION FROM AROUND MIDNIGHT FRIDAY THROUGH
SATURDAY, BRINGING HAZY SKIES, REDUCED VISIBILITY, AND DEGRADED
AIR QUALITY. NONETHELESS, EMBEDDED MOISTURE PATCHES WITHIN THE
TRADE WINDS WILL SUPPORT PASSING SHOWERS ACROSS THE USVI AND PR'S
WINDWARD SECTORS. AT THE SAME TIME, DAYTIME HEATING AND LOCAL
EFFECTS MAY TRIGGER ISOLATED TO SCATTERED AFTERNOON CONVECTION
ACROSS THE INTERIOR AND WESTERN PORTIONS OF PUERTO RICO.
LONG TERM(SUNDAY THROUGH THURSDAY)
ISSUED AT 303 AM AST THU JUN 18 2026
A TROPICAL WAVE IS EXPECTED TO APPROACH AND MOVE ACROSS THE
NORTHEASTERN CARIBBEAN FROM LATE SUNDAY INTO MONDAY, BRINGING A
SIGNIFICANT INCREASE IN MOISTURE ACROSS THE REGION. MODEL GUIDANCE
INDICATES PRECIPITABLE WATER VALUES RISING TO AROUND 2 INCHES, WITH
SURFACE AND MID-LEVEL RELATIVE HUMIDITY INCREASING TO ABOVE-NORMAL
LEVELS FOR THIS TIME OF YEAR. COMBINED WITH 500 MB TEMPERATURES NEAR
-7 DEGREES CELSIUS, THESE CONDITIONS WILL SUPPORT A MORE UNSTABLE
ATMOSPHERE AND ENHANCE THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS.
AS A RESULT, PERIODS OF MODERATE TO HEAVY RAINFALL ARE EXPECTED FROM
LATE SUNDAY THROUGH LATE MONDAY, WITH THE HIGHEST COVERAGE LIKELY
DURING THE AFTERNOON HOURS ACROSS WESTERN AND INTERIOR PUERTO RICO.
LOCALLY HEAVY DOWNPOURS OR FREQUENT SHOWERS MAY LEAD TO PONDING OF
WATER IN URBAN AND POORLY DRAINED AREAS, AS WELL AS ISOLATED
FLOODING CONCERNS.
BY TUESDAY INTO MIDWEEK, A DRIER AIR MASS WILL GRADUALLY FILTER INTO
THE REGION, IMPROVING WEATHER CONDITIONS. ALTHOUGH PASSING TRADE-
WIND SHOWERS WILL REMAIN POSSIBLE ACROSS WINDWARD AREAS, A RETURN TO
A MORE TYPICAL WEATHER PATTERN IS ANTICIPATED BY MIDWEEK.
THE PRIMARY HAZARDS DURING THE LONG-TERM PERIOD WILL BE PONDING OF
WATER AND FLOODING, ALONG WITH ISOLATED THUNDERSTORMS.
AVIATION
(06Z TAFS)
ISSUED AT 303 AM AST THU JUN 18 2026
A WEAK TROPICAL WAVE WILL MOVE BY THE REGION TODAY, FOLLOWED BY A
DENSE SAL LATE-TONIGHT. MAINLY VFR CONDS EXPECTED TO PREVAIL
ACROSS ALL TERMINALS THRU THE FCST PRD. HOWEVER, SHRA/TSRA WILL
DEVELOP ACROSS THE SURROUNDING WATERS, THE INTERIOR AND E-NW PR
BTWN 18/15-22Z, RESULTING IN BRIEF MVFR OR EVEN IFR CONDS,
ESPECIALLY AT JSJ/TJBQ, BUT IST/ISX COULD ALSO BE IMPACTED. EXPECT
E-ESE WINDS AT 10 OR LESS THRU 18/13Z, THEN AT 10-20 KT WITH
GUSTS BTWN 20-30KT NEAR SHRA/TSRA OR DUE TO SEA BREEZE.
MARINE
ISSUED AT 303 AM AST THU JUN 18 2026
A BROAD SURFACE HIGH PRESSURE BUILDING OVER THE CENTRAL ATLANTIC
WILL PROMOTE MODERATE TO LOCALLY FRESH EAST TO EAST-SOUTHEAST WINDS
OVER THE NEXT SEVERAL DAYS, RESULTING IN CHOPPY SEAS ACROSS THE
LOCAL WATERS AND CARIBBEAN PASSAGES. SMALL CRAFT SHOULD EXERCISE
CAUTION. SHOWER ACTIVITY WILL GRADUALLY INCREASE TODAY INTO
TOMORROW, FRIDAY, AS A TROPICAL WAVE APPROACHES THE CARIBBEAN BASIN,
LEADING TO LOCALIZED HEAVY RAINFALL, GUSTY WINDS, AND REDUCED
VISIBILITY. A DENSE LAYER OF SAHARAN DUST WILL ALSO GRADUALLY FILTER
INTO THE REGION BY THIS EVENING ONWARDS, RESULTING IN HAZY SKIES,
REDUCED VISIBILITY, AND POOR AIR QUALITY THROUGH THE WEEKEND.
ANOTHER TROPICAL WAVE WILL APPROACH THE AREA LATE IN THE WEEKEND.
BEACH FORECAST
ISSUED AT 303 AM AST THU JUN 18 2026
BREEZY TO LOCALLY WINDY CONDITIONS WILL MAINTAIN A LOW TO MODERATE
RISK OF RIP CURRENTS DURING THE NEXT FEW DAYS. AREAS UNDER A
MODERATE RISK OF RIP CURRENTS (LIFE-THREATENING RIP CURRENTS ARE
POSSIBLE IN THE SURF ZONE) TODAY INCLUDE, ST CROIX AND LATER THIS
EVENING NORTH-CENTRAL AND NORTHWESTERN PR AND CULEBRA.
THERE WILL BE A LOW RISK OF RIP CURRENTS FOR MOST OF THE REST OF
THE LOCAL BEACHES TODAY. HOWEVER, LIFE-THREATENING RIP CURRENTS
MAY STILL OCCUR, ESPECIALLY NEAR GROINS, JETTIES, REEFS, AND
PIERS.
THE MODERATE RISK IS FORECAST TO SPREAD ACROSS THE ISLANDS, WITH
MOST BEACHES BEING UNDER A MODERATE RISK TO START THE NEXT WEEK.
BEACHGOERS SHOULD ALSO REMAIN ALERT FOR DANGEROUS LIGHTNING NEAR
ISOLATED THUNDERSTORMS. SAHARAN DUST CONCENTRATIONS ARRIVING THIS
AFTERNOON ONWARDS WILL ALSO RESULT IN HAZY SKIES AND REDUCED AIR
QUALITY THROUGHOUT THE WEEKEND. HIGH HEAT INDICES WILL ALSO
PERSIST DURING THE FORECAST PERIOD, SENSITIVE GROUPS SHOULD TAKE
NECESSARY PRECAUTIONS.
FIRE WEATHER
ISSUED AT 303 AM AST THU JUN 18 2026
ALTHOUGH A WEAK TROPICAL WAVE WILL MOVE ACROSS THE ISLANDS TODAY,
KEEPING RH VALUES ABOVE CRITICAL LEVELS, THE EXTENSIVE DRY SOILS
AND HOT DAYTIME TEMPERATURES WILL COMBINE WITH SUSTAINED WINDS OF
10 TO 21 MPH WITH STRONGER GUSTS TO MAINTAIN AN ELEVATED FIRE
WEATHER RISK THROUGH LATE THIS AFTERNOON.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
KEY MESSAGES/SHORT TERM/AVIATION/FIRE WEATHER...CAM
LONG TERM....MMC
MARINE/BEACH FORECAST...MRR
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