944
FXCA62 TJSJ 300750
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
350 AM AST FRI MAY 30 2025
KEY MESSAGES
* FAST MOVING SHOWERS WILL CONTINUE TO MOVE ACROSS THE LOCAL
ISLANDS DURING THE MORNING HOURS. LATER IN THE AFTERNOON,
SHOWERS AND THUNDERSTORM ACTIVITY IS EXPECTED TO DEVELOP ACROSS
WESTERN PUERTO RICO.
* A DENSE SAHARAN AIR LAYER IS EXPECTED TO ARRIVE BY TOMORROW
NIGHT AND EARLY SUNDAY, RESULTING IN HAZY SKIES, REDUCED
VISIBILITIES, AND ADVERSE CONDITIONS FOR THE HEALTH OF SENSITIVE
GROUPS.
* WARM TO HOT CONDITIONS ARE LIKELY THIS WEEKEND, PARTICULARLY FOR
THE COASTAL AND URBAN AREAS OF THE ISLANDS.
SHORT TERM....SHORT-TERM...TODAY THROUGH SUNDAY
OVER THE PAST 24 HOURS, SATELLITE IMAGERY REVEALED A PERSISTENT MID-
TO HIGH-LEVEL CLOUD DECK ASSOCIATED WITH A TROUGH LOCATED TO THE
WEST OF THE REGION. WHILE THIS CLOUD COVER MAY HAVE HELPED LIMIT
WIDESPREAD CONVECTION, DOPPLER RADAR STILL OBSERVED SCATTERED
SHOWERS—PRIMARILY AFFECTING WINDWARD AREAS. THESE SHOWERS WERE
STEERED BY BREEZY EASTERLY WINDS RANGING FROM 10 TO 20 MPH,
OCCASIONALLY PRODUCING STRONGER GUSTS. RAINFALL AMOUNTS REMAINED
MODEST OVERALL DUE TO THE FAST MOVEMENT OF THE SHOWERS, WITH THE
HIGHEST ACCUMULATIONS NEARING 0.75 INCHES IN PARTS OF EASTERN PUERTO
RICO. TEMPERATURES VARIED SIGNIFICANTLY, WITH HIGHS NEAR 90°F ACROSS
SOUTHERN AND WESTERN PUERTO RICO AND LOWS AROUND 60°F IN THE
INTERIOR MOUNTAIN VALLEYS.
MARGINALLY UNSTABLE CONDITIONS WILL CONTINUE ACROSS THE REGION AS A
NEARLY STATIONARY MID-LEVEL RIDGE TO THE EAST MAINTAINS A TRADE WIND
CAP AND DRIER AIR ENTRAINMENT WHILE LINGERING UPPER-LEVEL TROUGHS TO
THE WEST ENHANCE DIVERGENCE ALOFT. ALTHOUGH THE RIDGE GENERALLY
PROMOTES CALM WEATHER, DIURNAL HEATING AND LOCAL INFLUENCES,
COMBINED WITH UPPER-LEVEL SUPPORT, WILL LIKELY RESULT IN SCATTERED
TO LOCALLY NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS DURING THE
AFTERNOON AND EVENING. VEERING BREEZY WINDS AT 15–20 MPH, GENERATED
BY A HIGH-PRESSURE SYSTEM OVER THE NORTH ATLANTIC, WILL INCREASE
WIND EXPOSURE ALONG THE COAST AND LOCAL ISLANDS, CONTRIBUTING TO A
GRADUAL WARMING TREND AND SUPPORTING ENHANCED OVERNIGHT AND EARLY
MORNING TRADE WIND SHOWERS. TYPICAL MOISTURE LEVELS WILL PERSIST
INITIALLY, BUT A TROPICAL WAVE PASSING SOUTH OF THE LOCAL ISLANDS
TODAY AND AN EASTERLY WIND SURGE CROSSING THE REGION FROM SATURDAY
INTO SUNDAY WILL INCREASE MOISTURE ADVECTION. THESE FEATURES, ALONG
WITH UPPER-LEVEL SUPPORT, WILL PUSH PRECIPITABLE WATER VALUES TO THE
HIGH END OF ABOVE-NORMAL LEVELS (AROUND 1.8 TO 1.9 INCHES) AND LOWER
500 MB TEMPERATURES NEAR -8ºC AS THE MID-LEVEL RIDGE WEAKENS.
WHILE CURRENT GUIDANCE FAVOR MORE LOCALIZED IMPACTS, SOME
UNCERTAINTY REMAINS REGARDING THE INFLUENCE OF UPPER-LEVEL TROUGHS,
WHICH COULD EITHER ENHANCE OR SUPPRESS MID- TO UPPER-LEVEL
CONVECTIVE ACTIVITY BEYOND EXPECTATIONS. IF CONVECTION IS ENHANCED,
INCREASED SHOWER AND THUNDERSTORM COVERAGE—WITH A SLIGHTLY HIGHER
RISK OF LOCALIZED FLOODING—MAY DEVELOP AS THE WEEKEND PROGRESSES;
HOWEVER, PERSISTENT CLOUD COVER, AS SEEN IN RECENT DAYS, COULD ACT
AS A LIMITING FACTOR BY SUPPRESSING CONVECTIVE DEVELOPMENT.
FOLLOWING THESE DISTURBANCES, A DENSE SAHARAN AIR LAYER (SAL) IS
EXPECTED TO GRADUALLY SPREAD ACROSS THE REGION STARTING SATURDAY
EVENING. ALTHOUGH THE DRIER AIR ALOFT ASSOCIATED WITH THE SAL MAY
REDUCE RAINFALL EFFICIENCY AND DEGRADE AIR QUALITY—PARTICULARLY FOR
SENSITIVE INDIVIDUALS—IT WILL ALSO PROMOTE SURFACE WARMING AND
INCREASED ATMOSPHERIC INSTABILITY, AS INDICATED BY ELEVATED VALUES
IN THE ECMWF EXTREME FORECAST INDEX AND THE GALVEZ-DAVIDSON INDEX,
RESPECTIVELY.
IN SUMMARY, THE OVERALL HAZARD RISK THROUGH THE FORECAST PERIOD
INCLUDES LIMITED EXCESSIVE RAINFALL AND LIGHTNING POTENTIAL EACH
DAY, MAINLY ACROSS NORTHWESTERN PUERTO RICO. HOWEVER, INCREASED
CLOUD COVER COULD EITHER ENHANCE OR SUPPRESS CONVECTIVE ACTIVITY,
SLIGHTLY ALTERING THE FLOODING POTENTIAL AS THE WEEKEND PROGRESSES.
SOUTHEASTERLY WINDS, COMBINED WITH THE APPROACHING DENSE SAL, WILL
RESULT IN INCREASING EXCESSIVE HEAT RISKS LATE IN THE WEEKEND.
BREEZY CONDITIONS WILL ALSO CONTRIBUTE TO LOCALIZED NON-THUNDERSTORM
WIND HAZARDS ALONG COASTAL ZONES AND THE LOCAL ISLANDS. FOR MORE
INFORMATION, PLEASE REFER TO THE EXPERIMENTAL GRAPHICAL HAZARDOUS
WEATHER OUTLOOK.
LONG TERM...MONDAY THROUGH FRIDAY
THE FORECAST CONTINUES ON TRACK WITH THE ENTRANCE OF A DENSE PLUME
OF SAHARAN AIR LAYER (SAL) AFFECTING THE NORTHEASTERN CARIBBEAN
THROUGH MID-WEEK. BASED ON THE LATEST MODEL GUIDANCE THE HIGHER
CONCENTRATIONS OF DUST ARE EXPECTED TO PEAK ON MONDAY WITH AEROSOL
OPTICAL THICKNESS OF NEAR 0.5. HAZY SKIES, DETERIORATED AIR QUALITY
AND REDUCED VISIBILITIES WILL CONTINUE THROUGH LATE WEDNESDAY.
DESPITE THE HIGHER CONCENTRATIONS ARE EXPECTED BY EARLY IN THE WEEK,
LOW TO MODERATE CONCETRATIONS OF DUST WILL CONTINUE THROUGH NEXT
WEEKEND. RESIDENTS AND VISITORS ARE URGED TO TAKE THE NECESSARY
HEALTH PRECAUTIONS DURING THIS PERIOD. AT THE SURFACE, A HIGH
PRESSURE SYSTEM WILL PROMOTE SOUTHEASTERLY WINDS THROUGH TUESDAY.
THE, WINDS ARE EXPECTED TO SHIFT FROM THE EAST AS THE SURFACE HIGH
MOVES TOWARDS THE NORTHEAST ATLANTIC. A MID-TO-UPPER LEVEL RIDGE
WILL BUILD OVER THE NORTHEASTERN CARIBBEAN BY MONDAY, PROMOTING
DRIER CONDITIONS AND STABILITY ALOFT. UNDER THESE CONDITIONS, VERY
LIMITED SHOWER ACTIVITY IS ANTICIPATED THROUGHOUT THE PERIOD WITH
PRECIPITABLE WATER VALUES (PWAT) NEAR BELOW-NORMAL CLIMATOLOGICAL
VALUES (1.5 INCHES). HOWEVER, SHOWERS AND ISOLATED THUNDERSTORMS
ARE POSSIBLE OVER WESTERN PUERTO RICO WITH THE COMBINATION OF
DIURNAL HEATING AND LOCAL EFFECTS. WARM TO HOT TEMPERATURES ARE
EXPECTED TOO, WITH TEMPERATURES RISING TO ABOVE NORMAL VALUES FOR
EARLY NEXT WEEK. HIGHS ARE EXPECTED TO BE IN THE UPPER 80S TO LOW
90S IN THE COASTAL AND URBAN AREAS, AND IN THE LOW 80S IN THE
HIGHER ELEVATIONS. HEAT INDICES COULD REACH VALUES OVER 108
DEGREES FAHRENHEIT ON MONDAY AND TUESDAY, PARTICULARLY OVER NORTH-
CENTRAL PUERTO RICO. PLEASE BE AWARE OF THESE CONDITIONS IF
PLANNING TO DO ACTIVITIES OUTDOORS, SCHOOL SUMMER CAMPS OR
CONSTRUCTION.
AVIATION
(06Z TAFS)
SHRA AROUND TJSJ THROUGH MOST OF THE PERIOD AND AFTERNOON SHRA/TSRA
AT TJBQ BETWEEN 30/17-23Z MAY RESULT IN BRIEF MVFR CONDITIONS AT
EITHER TERMINAL. SURFACE WINDS WILL REMAIN FROM THE EAST AT 8–10
KNOTS OVERNIGHT, INCREASING TO 14–18 KNOTS WITH HIGHER GUSTS AND SEA
BREEZE INFLUENCES AFTER 30/13Z, THEN DIMINISHING AFTER 30/23Z. GUSTY
AND VARIABLE WINDS ARE ALSO POSSIBLE IN AND AROUND ANY STRONG TSRA.
MARINE
A SURFACE HIGH PRESSURE BUILDING OVER THE ATLANTIC BASIN WILL
CONTINUE TO PROMOTE MODERATE TO LOCALLY FRESH TRADE WINDS OVER THE
NEXT FEW DAYS. SMALL CRAFT SHOULD EXERCISE CAUTION ACROSS MOST
OFFSHORE WATERS AND LOCAL CARIBBEAN PASSAGES. ISOLATED THUNDERSTORMS
ARE EXPECTED TO AFFECT THE WESTERN COASTAL WATERS OF PUERTO RICO AND
THE MONA PASSAGE EACH AFTERNOON AND EVENING. LOW CONCENTRATIONS OF
SAHARAN DUST WILL REMAIN OVER THE REGION THROUGH SATURDAY, THEN HAZY
SKIES AND REDUCED VISIBILITIES ARE EXPECTED FROM LATE SATURDAY
THROUGH MID-WEEK AS ANOTHER DENSE PLUME OF SAHARAN DUST MOVES TOWARD
THE AREA.
BEACH FORECAST
THERE IS A MODERATE RISK OF RIP CURRENT FOR NORTHERN BEACHES OF
PUERTO RICO AND SAINT CROIX. THE REST OF THE AREA, REMAINS UNDER A
LOW RISK OF RIP CURRENTS. PLEASE KEEP IN MIND THAT LIFE-
THREATENING RIP CURRENTS OFTEN OCCUR IN THE VICINITY OF GROINS,
JETTIES, REEFS, AND PIERS.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
MIDNIGHT SHIFT...ICP/GRS/ERG
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