944
FXCA62 TJSJ 180613
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
213 AM AST FRI SEP 18 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 213 AM AST FRI SEP 18 2026
- LINGERING MOISTURE FROM THE WAVE AND A LOW LEVELS OF SAHARAN
DUST ARE EXPECTED TODAY. WITH RAINFALL AND THUNDERSTORMS
EXPECTED OVER THE WESTERN SIDE OF PUERTO RICO DURING THE
AFTERNOON HOURS.
- SEASONAL CONDITIONS EXPECTED THROUGHOUT THE REST OF THE FORECAST
PERIOD FOR THE US VIRGIN ISLANDS AND PUERTO RICO.
- EXTREME HEAT RISK IS EXPECTED TO INCREASE ACROSS THE CWA, WITH RISK
LEVELS EXPECTED TO BE LIMITED TODAY, AND SIGNIFICANT INTO EARLY
NEXT WEEK.
- DECREASING WINDS WILL LEAD TO AMENABLE MARINE AND RIP CURRENT
CONDITIONS THROUGHOUT THE REST OF THE FORECAST PERIOD.
SHORT TERM(TODAY THROUGH SUNDAY)
ISSUED AT 213 AM AST FRI SEP 18 2026
ANOTHER ACTIVE 24 HOURS OF RAINFALL ACROSS THE CWA. RADAR ESTIMATES
SHOW 2 TO 4 INCHES OF RAIN ACCUMULATION ACROSS THE OFFSHORE WATERS,
NORTHWESTERN AND NORTHEASTERN PUERTO RICO AND VIEQUES. ON THE OTHER
HAND PORTIONS OF BASINS SUCH AS CARRAIZO AND LA PLATA RECEIVED
BETWEEN 1 TO 2 INCHES OF RAIN. THESE CONDITIONS CONTINUE TO PROVIDE
RELIEF TO THE ONGOING DROUGHT.
CONDITIONS WILL BECOME MORE SEASONAL INTO THE WEEKEND. LOW
CONCENTRATIONS OF SAHARAN DUST HAVE ENTERED THE US VIRGIN ISLANDS
AND PUERTO RICO OVERNIGHT AND WILL PERSIST INTO EARLY MORNING. A
DRIER MID-TO-LOW LEVEL (850 TO 500 HPA) AIR MASS WILL PERSIST ACROSS
THE REGION INTO THE EARLY AFTERNOON. THIS WILL ACT TO LIMIT RAINFALL
ACTIVITY DURING THE EARLY MORNING. HOWEVER, DUE TO THE PRESENCE OF
BREEZY ESE WIND FLOW ALONG WITH LINGERING MOISTURE, PASSING
ADVECTIVE SHOWERS ACROSS THE US VIRGIN ISLANDS AND EASTERN PUERTO
RICO CANNOT BE RULED OUT. THE ATMOSPHERIC COLUMN WILL BECOME MORE
HUMID INTO THE AFTERNOON. THIS ALONG WITH LOCAL EFFECTS WILL LEAD TO
THE DEVELOPMENT OF SHOWERS ACROSS INTERIOR AND WESTERN PUERTO RICO
DURING THE AFTERNOON WITH A LIMITED POTENTIAL FOR ISOLATED
THUNDERSTORMS. TODAY'S RISK FOR EXCESSIVE RAINFALL IS LIMITED WHICH
MEANS THAT FLOODING IN URBAN AREAS, ROADS, SMALL STREAMS, AND WASHES
ALONG WITH A LOW POTENTIAL FOR ISOLATED FLASH FLOODS IS POSSIBLE.
GIVEN RAINFALL ACTIVITY DURING THE PAST DAYS, WE CANNOT RULE OUT THE
POSSIBILITY OF LANDSLIDES OVER REGIONS OF HIGH TERRAIN, AS WELL AS
ACROSS PORTIONS OF NORTHWESTERN PUERTO RICO WHERE THE SOIL REMAINS
SATURATED FROM RECENT RAINFALL ACTIVITY.
BY SATURDAY INTO SUNDAY CONDITIONS ARE EXPECTED TO BECOME SEASONAL.
HUMID LOW-LEVELS AND SUB-SATURATED MID-LEVELS WILL PERSIST BOTH
DAYS. CONDITIONS ARE EXPECTED TO BECOME LESS WINDY INTO THE WEEKEND
WITH ESE WIND FLOW. WE EXPECT THE MOISTURE COUPLED WITH LOCAL
EFFECTS TO LEAD TO A PATTERN OF ISOLATED RAINFALL IN THE MORNING
HOURS ACROSS THE US VIRGIN ISLANDS AND EASTERN PUERTO RICO AND
INTERIOR AND NORTHWESTERN PUERTO RICO DURING THE AFTERNOON. THE RISK
FOR EXCESSIVE RAINFALL REMAINS ELEVATED THROUGH SUNDAY.
DUE TO THE WIDESPREAD CLOUD COVERAGE OVER THE REGION THE HEAT RISK
FOR TODAY REMAINS LIMITED ACROSS THE COASTAL AND URBAN AREAS.
HOWEVER SOME PLACES MIGHT FEEL WARMER THROUGHOUT THE DAY. WE
RECOMMEND INDIVIDUALS TO KEEP MONITORING THE WEATHER CONDITIONS AS
THEY EVOLVE AND CONTINUE CHECKING OFFICIAL FORUMS AS THE RISK
LEVELS MAY BE UPDATED LATER DURING THE DAY. THE RISK IS EXPECTED
TO BE SIGNIFICANT ON SATURDAY AND SUNDAY. IT IS RECOMMENDED THAT
INDIVIDUALS PURSUING OUTSIDE ACTIVITIES PLAN ACCORDINGLY AND
REMAIN HYDRATED AS THEY GO INTO THE WEEKEND.
LONG TERM(MONDAY THROUGH FRIDAY)
ISSUED AT 213 AM AST FRI SEP 18 2026
A MID- TO UPPER-LEVEL TROUGH WILL LINGER OVER THE ATLANTIC AND
NORTHEASTERN CARIBBEAN, SUPPORTING OCCASIONAL INDUCED SURFACE
PERTURBATIONS THROUGHOUT THE PERIOD. MEANWHILE, SURFACE HIGH
PRESSURE OVER THE CENTRAL ATLANTIC WILL MAINTAIN EAST TO EAST-
SOUTHEAST WINDS AND A GENERALLY WET ADVECTIVE PATTERN THROUGH MUCH
OF THE WORKWEEK. PASSING SHOWERS WILL AFFECT WINDWARD PORTIONS OF
PUERTO RICO AND THE U.S. VIRGIN ISLANDS, FOLLOWED BY AFTERNOON
SHOWERS AND ISOLATED THUNDERSTORMS OVER INTERIOR AND WESTERN PUERTO
RICO. CONVECTIVE DEVELOPMENT WILL SHIFT ACCORDING TO THE PREVAILING
STEERING FLOW. HOWEVER, THE STRONGEST AFTERNOON ACTIVITY WILL
GENERALLY FAVOR INTERIOR AND WESTERN PUERTO RICO, WHERE A LIMITED
FLOODING RAIN THREAT MAY DEVELOP EACH AFTERNOON. THE FLOODING THREAT
ELSEWHERE ACROSS THE ISLANDS WILL BE REASSESSED AS THE PERIOD
APPROACHES.
A WARMING TREND WILL CONTINUE AT LEAST DURING THE FIRST HALF OF THE
WEEK. NEAR- TO ABOVE-NORMAL MOISTURE, COMBINED WITH LIMITED
VENTILATION ACROSS URBAN AND COASTAL AREAS, COULD RESULT IN PERIODS
OF ELEVATED TO LOCALLY SIGNIFICANT HEAT RISK. GUIDANCE THEN
INDICATES A DRYING TREND DURING THE LATTER PART OF THE WEEK AS
PRECIPITABLE WATER DECREASES TO NEAR OR BELOW NORMAL LEVELS.
THE UPPER-LEVEL TROUGH WILL ALSO MAINTAIN STRONG VERTICAL WIND SHEAR
ACROSS THE REGION, CREATING AN UNFAVORABLE ENVIRONMENT FOR TROPICAL
CYCLONE DEVELOPMENT. LOCAL SEA-BREEZE VARIATIONS ARE EXPECTED DURING
THE DAY, WITH LAND-BREEZE INFLUENCES POSSIBLE OVERNIGHT ALONG
COASTAL AREAS.
AVIATION
(06Z TAFS)
ISSUED AT 213 AM AST FRI SEP 18 2026
MOSTLY VFR CONDS EXPECTED THROUGH THE PERIOD. HOWEVER, SHRA/TSRA
WILL LIKELY AFFECT TJBQ AND THE VICINITY OF TJSJ/TJPS, WITH BRIEF
MVFR/IFR PSBL AT TJBQ. VCSH EXPECTED ACROSS USVI TERMINALS AND TJSJ
AFTER 18/23Z. LIGHT AND VARIABLE WIND BECOMING E-ESE WINDS AT 10-15
KT WITH GUSTS AFTER 18/13Z. LIGHT AND VARIABLE WINDS RETURN AFTER
18/23Z.
MARINE
ISSUED AT 213 AM AST FRI SEP 18 2026
A SURFACE HIGH PRESSURE SYSTEM OVER THE WESTERN INTO CENTRAL
ATLANTIC WILL DOMINATE THE REGIONAL WEATHER PATTERN, LEADING TO
GENTLE TO MODERATE EAST-SOUTHEASTERLY WINDS FOR THE NEXT FEW DAYS.
TROPICAL MOISTURE WILL MOVE OVER THE AREA LATER TODAY INTO THE
WEEKEND AND EARLY NEXT WEEK, ENHANCING THE POTENTIAL FOR ISOLATED
THUNDERSTORMS AND LOCALIZED HAZARDOUS MARINE CONDITIONS.
BEACH FORECAST
ISSUED AT 213 AM AST FRI SEP 18 2026
A MODERATE RISK OF RIP CURRENTS WILL BE IN EFFECT TODAY ALONG
NORTHERN PUERTO RICO BEACHES, WITH LOW RISK ELSEWHERE. AS WINDS
DIMINISH, THE RIP CURRENT RISK WILL DROP TO LOW ACROSS ALL LOCAL
BEACHES THROUGH EARLY NEXT WEEK, RETURNING TO MODERATE BY MIDWEEK AS
WINDS STRENGTHEN. DESPITE THE LOWER OVERALL RISK, LOCALIZED LIFE-
THREATENING RIP CURRENTS REMAIN POSSIBLE NEAR PIERS, GROINS, REEFS,
AND JETTIES. ADDITIONALLY, DAILY DIURNAL CONVECTION WILL CONTINUE TO
GENERATE AFTERNOON SHOWERS AND ISOLATED THUNDERSTORMS ACROSS WESTERN
AND NORTHWESTERN PUERTO RICO, BRINGING LOCALIZED HAZARDS OF
LIGHTNING AND GUSTY WINDS. BEACHGOERS SHOULD MONITOR CHANGING
CONDITIONS AND SEEK SHELTER IMMEDIATELY. ADDITIONALLY, AN ELEVATED
TO SIGNIFICANT HEAT RISK IS FORECAST OVER THE COMING DAYS, ENHANCING
POTENTIAL HEAT IMPACTS. RESIDENTS AND VISITORS SHOULD REMAIN
HYDRATED AND LIMIT PROLONGED SUN EXPOSURE DURING PEAK AFTERNOON
HEATING. FOLLOW GUIDANCE FROM LOCAL HEALTH OFFICIALS.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
EVE... LIS/KML/MMC
MID... ICP/RVM
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