303
FXCA62 TJSJ 161818
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
218 PM AST WED SEP 16 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 159 PM AST WED SEP 16 2026
- AN APPROACHING TROPICAL WAVE WILL CONTINUE TO PROMOTE SHOWERS
AND THUNDERSTORMS ACROSS THE U.S. VIRGIN ISLANDS AND PUERTO RICO
THROUGH THE REST OF THE AFTERNOON INTO THURSDAY, INCREASING THE
POTENTIAL FOR FLOODING AND LIGHTNING RISKS.
- THERE IS A LOW TO MODERATE RISK OF RIP CURRENTS THROUGH THE
WEEKEND ALONG THE BEACHES OF THE U.S. VIRGIN ISLANDS AND PUERTO
RICO.
- LIMITED EXTREME HEAT RISKS ARE EXPECTED FOR THE REST OF TODAY
AND THURSDAY, WITH ELEVATED TO SIGNIFICANT HAZARD RISKS
RETURNING FRIDAY INTO THE WEEKEND.
- WEATHER CONDITIONS ARE EXPECTED TO IMPROVE BY THURSDAY EVENING
INTO FRIDAY, AS A DRIER AIRMASS AND LOW CONCENTRATIONS OF
SAHARAN DUST FILTER INTO THE AREA.
SHORT TERM(THIS EVENING THROUGH FRIDAY)
ISSUED AT 159 PM AST WED SEP 16 2026
A FEW PASSING SHOWERS HAVE REACHED THE U.S. VIRGIN ISLANDS AND
EASTERN PORTIONS OF PUERTO RICO. THE COMBINATION OF AN APPROACHING
MOIST, UNSTABLE TROPICAL WAVE, A NEARBY UPPER-LEVEL LOW, AND LOCAL
EFFECTS—SUCH AS DIURNAL HEATING, OROGRAPHIC LIFT, AND SEA-BREEZE
CONVERGENCE—WILL FUEL DEEP CONVECTION TODAY. THE AXIS OF THE
TROPICAL WAVE IS CURRENTLY CROSSING THE U.S. VIRGIN ISLANDS;
HOWEVER, THE MAIN MOISTURE FIELD IS PRECEDING IT. CONSEQUENTLY,
SHOWER ACTIVITY AND ISOLATED THUNDERSTORMS WILL INCREASE ACROSS THE
ISLANDS THIS AFTERNOON AS THE WAVE MOVES THROUGH THE FORECAST AREA
(CWA). THE MOST ACTIVE WEATHER IS EXPECTED OVERNIGHT, WITH ACTIVITY
RAMPING UP ACROSS THE U.S. VIRGIN ISLANDS, EASTERN PUERTO RICO, AND
THE METROPOLITAN AREAS BEFORE EXTENDING INTO THE INTERIOR AND
WESTERN REGIONS. PRECIPITABLE WATER (PWAT) VALUES WILL EXCEED
SEASONAL VALUES (1.95–2.30 INCHES) BY THIS AFTERNOON AS WAVE-
ASSOCIATED MOISTURE MOVES IN. UNSTABLE ATMOSPHERIC CONDITIONS WILL
PREVAIL, SUPPORTED BY STEEP MID-LEVEL LAPSE RATES (700–500 MB)
REACHING OVER 6.5 °C/KM. THE BULK MOISTURE ASSOCIATED TO THE WAVE
WILL REMAIN UNTIL THURSDAY EVENING. DRIER AIR IS FORECASTED TO
APPROACH THE ISLANDS BY FRIDAY, WHICH COULD LIMIT CONVECTION,
HOWEVER SHOWERS AND THUNDERSTORMS ACTIVITY IS STILL POSSIBLE.
MOSTLY ADVECTIVE SHOWERS ARE EXPECTED DURING MORNING HOURS ON
THURSDAY, ALONG ISOLATED THUNDERSTORMS. THE UPPER-LEVEL LOW IS
EXPECTED TO DEPART THE REGION TOMORROW, HOWEVER, IT SHOULD STILL
SUPPORT INSTABILITY COMBINED WITH THE TROPICAL WAVE. ALTHOUGH
LIMITED DAYTIME HEATING COULD LIMIT DEEP CONVECTION IN THE
AFTERNOON, SHOWERS AND THUNDERSTORMS ARE STILL EXPECTED. BASED ON
THIS SCENARIO, THE RISK OF EXCESSIVE RAINFALL REMAINS ELEVATED FOR
THE REST OF TODAY AND TOMORROW ACROSS EASTERN, NORTHERN, INTERIOR
AND WESTERN PORTIONS. A LIMITED EXCESSIVE RAINFALL RISK IS EXPECTED
ON THE U.S. VIRGIN ISLANDS AND REST OF THE AREA. THESE RISK LEVELS
FROM LIMITED TO MODERATE WILL PERSISTS UNTIL FRIDAY. THESE RISKS
MEANS THAT FLOODING IS POSSIBLE IN URBAN AREAS, ROADS, SMALL STREAMS
AND WASHES, AND A LOW CHANCE OF URBAN AND SMALL STREAMS IS PRESENT.
ALSO, OVER MOST AREAS, PONDING OF WATERS IN ROADS AND POORLY DRAINED
AREAS IS POSSIBLE.
THE HEAT RISK REMAINS LIMITED UNTIL THURSDAY DUE TO CLOUD COVER
ASSOCIATED WITH THE TROPICAL WAVE. HOWEVER, THE RISK WILL INCREASE
BY FRIDAY AS A DRIER AIR MASS ALONG WITH SAHARAN DUST FILTERS INTO
THE AREA.
LONG TERM(SATURDAY THROUGH NEXT TUESDAY)
ISSUED AT 159 PM AST WED SEP 16 2026
DURING THE EARLY PART OF THE LONG-TERM PERIOD, AN UPPER-LEVEL LOW
NORTHEAST OF THE CARIBBEAN WILL INDUCE ABOVE-NORMAL LOW-LEVEL
MOISTURE ACROSS THE REGION, WHILE A WEAK SURFACE HIGH PRESSURE NORTH-
NORTHWEST OF THE AREA DRAWS AN EAST-SOUTHEASTERLY WIND FLOW OVER THE
LOCAL AREA. PRECIPITABLE WATER (PWAT) VALUES BETWEEN 2.0 AND 2.2
INCHES ARE EXPECTED, REMAINING SLIGHTLY ABOVE NORMAL FOR THIS TIME
OF YEAR. DESPITE THIS MOISTURE, A MID-TO-UPPER LEVEL RIDGE WILL
DOMINATE THE AREA, MAINTAINING UNFAVORABLE UPPER-LEVEL CONDITIONS
AND SUSTAINING A SEASONAL PATTERN. PASSING SHOWERS ARE EXPECTED
DURING THE MORNING HOURS ACROSS THE REGIONAL WATERS AND WINDWARD
SECTIONS OF THE ISLANDS, FOLLOWED BY AFTERNOON SHOWERS AND ISOLATED
THUNDERSTORMS OVER THE INTERIOR AND WESTERN SECTIONS OF PUERTO RICO,
AS WELL AS DOWNWIND FROM EL YUNQUE, PUERTO RICO'S SMALLER ISLANDS
AND THE US VIRGIN ISLANDS. BY SUNDAY, WINDS ARE EXPECTED TO SHIFT TO
SOUTHEASTERLY, FOCUSING AFTERNOON CONVECTION PRIMARILY OVER THE
INTERIOR AND NORTHWESTERN PUERTO RICO. WEAK STEERING WINDS AROUND 10
KNOTS WILL ELEVATE THE FLOOD RISK WHERE PERSISTENT SHOWERS DEVELOP.
BY SUNDAY NIGHT INTO EARLY NEXT WEEK, THE MOIST SOUTHEASTERLY FLOW
WILL PULL MORE TROPICAL MOISTURE INTO THE AREA, HOLDING PWAT VALUES
AROUND 2.0 INCHES (SEASONAL TO SLIGHTLY ABOVE NORMAL). THE MID-TO-
UPPER LEVEL RIDGE AND THE UPPER-LEVEL LOW TO THE NORTHEAST WILL BOTH
REMAIN IN PLACE, CONTINUING THE SEASONAL REGIME UNDER EAST-
SOUTHEASTERLY WINDS. MORNING SHOWERS WILL FAVOR EASTERN AND
SOUTHEASTERN PORTIONS OF THE ISLANDS, INCLUDING THE US VIRGIN
ISLANDS, WITH AFTERNOON CONVECTION CONCENTRATING ACROSS THE INTERIOR
AND NORTHWESTERN QUADRANT OF PUERTO RICO. WITH 500 MB TEMPERATURES
HOVERING NEAR -6°C, ISOLATED AFTERNOON THUNDERSTORMS WILL REMAIN
POSSIBLE EACH DAY. ADDITIONALLY, THE MOIST SOUTHEASTERLY FLOW WILL
DRIVE AN ELEVATED HEAT RISK FROM SUNDAY ONWARD, PRIMARILY IMPACTING
HEAT-SENSITIVE INDIVIDUALS WITHOUT ACCESS TO EFFECTIVE COOLING OR
HYDRATION.
BY MID-WEEK, A TROPICAL WAVE MAY APPROACH THE AREA, THOUGH FORECAST
UNCERTAINTY REMAINS DUE TO MODEL DISAGREEMENT, WITH THE GFS BRINGING
THE WAVE CLOSER TO THE LOCAL AREA, WHILE THE ECMWF PULLS IT TO THE
NORTH. PLEASE CONTINUE TO MONITOR THE FORECAST FOR FUTURE UPDATES AS
GUIDANCE RESOLVES.
AVIATION
(18Z TAFS)
ISSUED AT 159 PM AST WED SEP 16 2026
A COMBINATION OF VFR AND MVFR CONDS ARE EXPCD ACROSS ALL TAF SITES,
AS A TROPCL WAVE MOVES ACROSS THE CWA, BRINGING -TSRA/+TSRA
THROUGHOUT THE TAF PRD. TEMPOS BTWN 16/18-20 OVER JSJ AND ISX DUE TO
REDUCED CIGS/VIS, LEADING TO MVFR/IFR CONDS. AMDS WILL BE ISSUED IF
REQUIRED. ELSEWHERE, MAINLY VCTS WITH PROB30S BTWN THE 12/06-16 PRD
FOR THE EASTERN TAF SITES OF PR AND USVI DUE TSRA. E-SE WINDS BTWN
12 - 18 KT WITH GUSTS UP TO 25 - 28 KT THROUGH 16/22 - 23Z, SLIGHTLY
WEAKENING AND BECOMING 5 - 10 KT. WINDS SHOULD STRENGTHEN ONCE
AGAIN BTWN 10 - 15 KT, GUSTS UP TO 25 KT, BY 17/12-13Z.
MARINE
ISSUED AT 159 PM AST WED SEP 16 2026
AN APPROACHING TROPICAL WAVE AND A BROAD SURFACE HIGH WILL MAINTAIN
WINDS AROUND 10 TO 20 KNOTS, RESULTING IN PERIODS OF LOCALLY LIGHT
TO MODERATE CHOP. THE MOST UNSETTLED CONDITIONS ARE EXPECTED TONIGHT
INTO THURSDAY, WITH INCREASED SHOWERS AND THUNDERSTORMS. SMALL CRAFT
OPERATORS SHOULD EXERCISE CAUTION. CONDITIONS WILL GRADUALLY IMPROVE
FRIDAY AS THE WAVE MOVES WEST, WITH MODERATE EASTERLY TRADE WINDS
PERSISTING THROUGH THE WEEKEND.
BEACH FORECAST
ISSUED AT 159 PM AST WED SEP 16 2026
EXPECT A LOW TO MODERATE RISK OF RIP CURRENTS ACROSS PUERTO RICO AND
THE U.S. VIRGIN ISLANDS, AS A TROPICAL WAVE MOVES ACROSS REGION
TONIGHT INTO THURSDAY. THIS WILL BRING WINDS OF 17 TO 23 MPH, ALONG
WITH SQUALLY SHOWERS AND THUNDERSTORMS. BEACHGOERS SHOULD SEEK
SHELTER IMMEDIATELY IF THUNDER IS HEARD. REMEMBER, LIFE-THREATENING
RIP CURRENTS CAN STILL OCCUR DURING LOW-RISK CONDITIONS,
PARTICULARLY NEAR GROINS, JETTIES, REEFS, AND PIERS. A MORE
WIDESPREAD MODERATE RISK IS FORECAST FRIDAY ALONG THE NORTH-FACING
BEACHES OF PUERTO RICO, FOLLOWED BY A GENERALLY LOW RISK THROUGH THE
WEEKEND.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
KEY MESSAGES...GRS
SHORT TERM...GRS/MNG/JCP
LONG TERM...CAM/KML
MARINE/BEACH FORECAST...MMC
AVIATION...MNG
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