613
FXCA62 TJSJ 310900
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
500 AM AST SAT MAY 31 2025
KEY MESSAGES
* AN EXTENSIVE AND DENSE PLUME OF SAHARAN AIR LAYER (SAL) WILL
AFFECT THE LOCAL ISLANDS FROM TODAY INTO THE MIDDLE OF THE
UPCOMING WORKWEEK. THIS WILL RESULT IN HAZY SKIES, LIMITED
COVERAGE IN SHOWER ACTIVITY, AND WARMER CONDITIONS.
* AN INCREASE IN SURFACE WINDS WILL INDUCE SOME MODERATE TO
LOCALLY FRESH WINDS, RESULTING IN WIND-DRIVEN SEAS. THEREFORE,
SMALL CRAFT OPERATORS SHOULD EXERCISE CAUTION.
SHORT TERM...TODAY THROUGH MONDAY
A CLOUD DECK PRESENT IN THE MID-TO-UPPER LEVELS OF THE ATMOSPHERE
CONTRIBUTED TO VARIABLY CLOUDY SKIES OVERNIGHT ACROSS THE REGION.
ADDITIONALLY, THE ARRIVAL OF A SAHARAN AIR LAYER (SAL) RESULTED IN
SOMEWHAT HAZY CONDITIONS. OVERNIGHT LOW TEMPERATURES RANGED FROM THE
MID-60S IN THE MOUNTAIN REGIONS TO THE MID-70S ALONG THE COASTAL
AREAS. DOPPLER RADAR DETECTED A FEW ISOLATED SHOWERS DEVELOPING
ALONG THE WINDWARD SECTIONS OF THE ISLANDS, ADVECTED BY AN EAST-
SOUTHEAST WIND FLOW, BUT LOCALIZED LAND BREEZE EFFECTS WERE ALSO
NOTED.
A MID-LEVEL RIDGE NEARLY STATIONARY OVER THE REGION WILL CONTINUE TO
SUPPORT A TRADE WIND INVERSION, EFFECTIVELY SUPPRESSING DEEP
CONVECTIVE DEVELOPMENT ACROSS PUERTO RICO AND THE U.S. VIRGIN
ISLANDS. THIS SYNOPTIC PATTERN, COMBINED WITH THE ARRIVAL OF A
SAHARAN AIR LAYER (SAL), WILL FURTHER DRY OUT THE ATMOSPHERE ABOVE
850 MB, LIMITING VERTICAL MOISTURE AVAILABILITY OVER THE NORTHEAST
CARIBBEAN. DESPITE THIS DRYING TREND, POCKETS OF MOISTURE EMBEDDED
WITHIN THE PREVAILING WINDS, ASSOCIATED WITH A WIND SURGE, WILL
BRING OCCASIONAL SHOWERS ACROSS PORTIONS OF THE ISLANDS, ESPECIALLY
IN THE WINDWARD LOCATIONS. AS THE WIND SURGE PROGRESSES, RESIDENTS
CAN EXPECT A NOTICEABLE INCREASE IN LOCAL WINDS THROUGHOUT THE
WEEKEND, ESPECIALLY DURING THE LATE MORNING AND AFTERNOON HOURS.
AFTERNOON CONVECTION WILL REMAIN CONFINED TO THE NORTHWEST QUADRANT
OF PUERTO RICO, DRIVEN BY LOCAL SEA BREEZE CONVERGENCE AND DIURNAL
HEATING, BUT WIDESPREAD THUNDERSTORM ACTIVITY IS NOT ANTICIPATED DUE
TO THE PREVAILING DRY AIR AND STABLE CONDITIONS. THE SAL, EXPECTED
TO ARRIVE LATER TODAY AND PERSIST INTO EARLY NEXT WEEK, WITH A PEAK
AROUND MONDAY, IS LIKELY TO RESULT IN HAZY SKIES, REDUCED
VISIBILITY, AND MINIMAL RAINFALL. AS SAL CONCENTRATIONS INCREASE,
NIGHTTIME RADIATIONAL COOLING WILL BE LIMITED, LEADING TO WARMER-
THAN-AVERAGE MINIMUM TEMPERATURES EACH NIGHT AND EARLY MORNING HOURS
ACROSS THE ISLANDS. THEREFORE, WE EXPECT A WARM TO HOT PERIOD IN THE
COMING DAYS, WITH ELEVATED HEAT INDICES AND ABOVE-NORMAL
TEMPERATURES.
THE PRESENCE OF SAHARAN DUST WILL LEAD TO HAZY SKIES AND REDUCED AIR
QUALITY ACROSS THE REGION. INDIVIDUALS WITH RESPIRATORY CONDITIONS,
SUCH AS ASTHMA OR ALLERGIES, SHOULD LIMIT OUTDOOR ACTIVITIES AND USE
PROTECTIVE MEASURES AS NEEDED. STAYING HYDRATED AND AVOIDING
STRENUOUS OUTDOOR EXERCISE DURING PEAK HEAT HOURS IS ALSO
RECOMMENDED.
LONG TERM...TUESDAY TROUGH SATURDAY
THE LONG-TERM FORECAST REMAINS ON TRACK. ACCORDING TO THE NASA
GODDARD EARTH OBSERVING SYSTEM MODEL V5, A DENSE PLUME OF SAHARAN
AIR LAYER (SAL) WILL CONTINUE TO AFFECT THE NORTHEASTERN CARIBBEAN
THROUGH MIDWEEK. THE MODEL INDICATES THAT THE HIGHEST
CONCENTRATIONS ARE EXPECTED EARLY IN THE PERIOD, WITH AEROSOL
OPTICAL THICKNESS VALUES NEARING 0.5. THIS PATTERN WILL RESULT IN
HAZY SKIES, REDUCED VISIBILITIES, AND DETERIORATED AIR QUALITY
THROUGH AT LEAST WEDNESDAY. ALTHOUGH THE MOST INTENSE DUST
PRESENCE IS FORECAST FOR THE FIRST PART OF THE WEEK, LOW TO
MODERATE CONCENTRATIONS ARE EXPECTED TO LINGER INTO THE UPCOMING
WEEKEND. RESIDENTS AND VISITORS, PARTICULARLY THOSE WITH
RESPIRATORY CONDITIONS, ARE ADVISED TO TAKE APPROPRIATE HEALTH
PRECAUTIONS DURING THIS PERIOD. AT THE SURFACE, A HIGH-PRESSURE
SYSTEM WILL PROMOTE SOUTHEASTERLY WINDS THROUGH TUESDAY, GRADUALLY
SHIFTING FROM THE EAST AS THE HIGH MOVES INTO THE CENTRAL
ATLANTIC.
A MID- TO UPPER-LEVEL RIDGE IS FORECAST TO STRENGTHEN OVER THE
REGION DURING THE EARLY PART OF THE WEEK, FAVORING A DRIER AND
MORE STABLE ENVIRONMENT ALOFT. PRECIPITABLE WATER VALUES WILL
REMAIN BELOW CLIMATOLOGICAL NORMALS, NEAR OR BELOW 1.5 INCHES,
LIMITING OVERALL SHOWER ACTIVITY ACROSS THE AREA. HOWEVER, LOCALLY
INDUCED SHOWERS AND ISOLATED THUNDERSTORMS REMAIN POSSIBLE EACH
AFTERNOON ACROSS WESTERN PUERTO RICO, DUE TO DIURNAL HEATING AND
LOCAL EFFECTS. TEMPERATURES WILL REMAIN ABOVE NORMAL, WITH HIGHS
RANGING FROM THE UPPER 80S TO LOW 90S FAHRENHEIT IN COASTAL AND
URBAN AREAS, AND IN THE LOW 80S ACROSS HIGHER ELEVATIONS. HEAT
INDICES MAY EXCEED 108°F DURING THE PEAK OF THE EVENT,
PARTICULARLY ACROSS NORTH-CENTRAL PUERTO RICO. THESE HOT AND DRY
CONDITIONS, COMBINED WITH POOR AIR QUALITY, COULD POSE ADDITIONAL
HEALTH RISKS, ESPECIALLY FOR THE MORE VULNERABLE POPULATIONS.
AVIATION
(06Z TAFS)
MAINLY VFR CONDITIONS ACROSS THE TERMINALS. ANY SHRA WILL BE
BRIEFED, WITH MINIMAL IMPACT ON OPERATIONS FOR MOST TERMINALS.
EXPECT WINDS FROM THE ESE TO RANGE AT 15-20 KTS AFTER 31/13Z, WITH
HIGHER GUSTS AROUND 25 KT OR MORE. HOWEVER, THEY ARE EXPECTED TO
RETURN TO 10 KT OR LESS OVERNIGHT (AFTER 31/22Z). VCSH WILL DEVELOP
NEAR TJBQ DURING THE AFTERNOON HOURS, BUT WE ARE NOT ANTICIPATING
WIDESPREAD ACTIVITY. A SAL WILL BRING HAZY SKIES, BUT VISIBILITY
WILL RANGE AROUND 6SM, ESPECIALLY FROM THIS AFTERNOON ONWARD.
MARINE
A SURFACE HIGH-PRESSURE SYSTEM STRENGTHENING OVER THE ATLANTIC
BASIN WILL CONTINUE TO SUPPORT MODERATE TO LOCALLY FRESH EASTERLY
TRADE WINDS DURING THE NEXT FEW DAYS. MARINERS SHOULD REMAIN
CAUTIOUS, PARTICULARLY ACROSS OFFSHORE ATLANTIC WATERS AND THE
CARIBBEAN PASSAGES, WHERE CHOPPY SEAS ARE EXPECTED. EACH AFTERNOON
AND EVENING, ISOLATED THUNDERSTORMS MAY DEVELOP AND IMPACT THE
MONA PASSAGE AND WESTERN COASTAL WATERS OF PUERTO RICO DUE TO
LOCALIZED CONVERGENCE. BY LATE TODAY INTO THE MIDDLE OF NEXT
WEEK, ANOTHER SIGNIFICANT SURGE OF SAHARAN DUST IS FORECAST TO
REACH THE REGION, LEADING TO HAZY SKIES AND REDUCED VISIBILITY.
BEACH FORECAST
A MODERATE RISK OF RIP CURRENTS IS IN EFFECT FOR NORTH-FACING
BEACHES OF PUERTO RICO AND THE ISLAND OF SAINT CROIX. ELSEWHERE,
THE RISK REMAINS LOW. NONETHELESS, SWIMMERS ARE URGED TO USE
CAUTION, ESPECIALLY NEAR PIERS, REEFS, AND OTHER STRUCTURES WHERE
DANGEROUS RIP CURRENTS ARE MORE LIKELY TO FORM UNEXPECTEDLY.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM & AVIATION...CAM
LONG TERM & MARINE....LIS
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