698
FXCA62 TJSJ 160901
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
501 AM AST TUE SEP 16 2025
KEY MESSAGES
* A DEPARTING PERTURBATION WILL RESULT IN PASSING SHOWERS THIS
MORNING, FOLLOWED BY AFTERNOON CONVECTION OVER THE INTERIOR
AND WESTERN TO SOUTHWESTERN PUERTO RICO.
* A TROPICAL WAVE COMBINED WITH AN UPPER-LEVEL TROUGH, WILL
INCREASE THE FREQUENCY OF SHOWERS AND THUNDERSTORMS PARTICULARLY
WEDNESDAY AND THURSDAY. AS A RESULT, THE RISK OF FLOODING WILL
REMAIN ELEVATED.
* THE VIRGIN ISLANDS WILL ALSO EXPERIENCE AN INCREASE IN SHOWERS
AND THUNDERSTORMS, POTENTIALLY LEADING TO WATER SURGES IN
DRAINAGE GUTS, PONDING ON ROADWAYS, OCCASIONAL LIGHTNING, AND
ISOLATED LANDSLIDES.
* A HEAT ADVISORY IS IN EFFECT TODAY ACROSS COASTAL AND URBAN
AREAS OF PUERTO RICO, AS WELL AS VIEQUES, CULEBRA AND THE
VIRGIN ISLANDS. INCREASING HEAT RISK IS FORECAST AGAIN TOWARD
THE END OF THE WEEK AND INTO THE WEEKEND.
* THERE IS A MODERATE RISK OF RIP CURRENTS ACROSS THE NORTHERN
AND EASTERN BEACHES OF PUERTO RICO, AS WELL AS CULEBRA AND ST.
CROIX TODAY. A LOW RISK IS EXPECTED IN OTHER AREAS.
SHORT TERM...TODAY THROUGH THURSDAY
SHOWERS AND THUNDERSTORMS MOVED ACROSS THE REGION OVERNIGHT,
AFFECTING THE NORTHEASTERN HALF OF PUERTO RICO, THE U.S. VIRGIN
ISLANDS, AND THE LOCAL ISLANDS, WITH SOME ACTIVITY BRUSHING THE
NORTHERN COAST. RADAR SHOWS PEAK RAINFALL NEAR 1 INCH IN
SOUTHEASTERN RIO GRANDE AND ALONG THE COAST FROM VEGA BAJA TO
VEGA ALTA. OVERNIGHT LOWS STAYED WARM IN EASTERN PUERTO RICO, THE
U.S. VIRGIN ISLANDS, AND THE LOCAL ISLANDS (80–82°F), WHILE THE
CENTRAL INTERIOR COOLED INTO THE MID-60S. WINDS WERE MOSTLY LIGHT
AND VARIABLE, WITH BRIEF GUSTS NEAR THUNDERSTORMS.
A DEPARTING TROPICAL WAVE WILL LEAVE ENOUGH MOISTURE IN PLACE, AND
MARGINAL INSTABILITY WILL CONTINUE TO SUPPORT SHOWERS AND A FEW
THUNDERSTORMS THIS MORNING, MAINLY AFFECTING WINDWARD AREAS. THIS
AFTERNOON, HEAT AND MOISTURE WILL FUEL STRONGER THUNDERSTORMS ACROSS
THE WESTERN INTERIOR AND WESTERN PUERTO RICO. THESE STORMS MAY BRING
HEAVY RAINFALL, LOCALIZED FLOODING, LIGHTNING IMPACTS, AND GUSTY
WINDS. WITH SOILS ALREADY SATURATED FROM RECENT RAINS, THE RISK OF
FLASH FLOODING AND LANDSLIDES IN STEEP TERRAIN IS ELEVATED.
TEMPERATURES WILL REMAIN VERY HOT, WITH A HEAT ADVISORY IN EFFECT
FROM 10 AM TO 5 PM FOR COASTAL AND URBAN AREAS OF PUERTO RICO,
VIEQUES, CULEBRA, AND THE U.S. VIRGIN ISLANDS.
ANOTHER TROPICAL WAVE WILL CROSS THE EASTERN CARIBBEAN TONIGHT INTO
WEDNESDAY, WITH ABUNDANT MOISTURE LINGERING THROUGH THURSDAY. AT THE
SAME TIME, AN UPPER-LEVEL TROUGH WILL MAKE THE ATMOSPHERE MORE
FAVORABLE FOR THUNDERSTORM DEVELOPMENT, ESPECIALLY WEDNESDAY INTO
THURSDAY. LIGHTER WINDS MIDWEEK WILL CAUSE SHOWERS AND STORMS TO
MOVE MORE SLOWLY, INCREASING THE RISK OF FLOODING IMPACTS ACROSS A
BROADER AREA. WITH PLENTY OF HEAT AND MOISTURE IN PLACE, EXPECT
ACTIVE SHOWERS AND THUNDERSTORMS, WHILE CLOUDS AND RAIN MAY BRING
OCCASIONAL RELIEF FROM THE PERSISTENT DANGEROUS HEAT.
LONG TERM...FRIDAY THROUGH TUESDAY
FOR FRIDAY AND SATURDAY, THE UPPER-LEVEL TROUGH WILL WEAKEN,
ALLOWING A WEAK MID-LEVEL HIGH PRESSURE TO SLIGHTLY DOMINATE. THE
LATEST MODEL GUIDANCE SUGGESTS THAT PRECIPITABLE WATER (PWAT)
VALUES WILL REMAIN WITHIN THE NORMAL RANGE FOR THIS TIME OF YEAR,
RANGING FROM 2.0 INCHES ON FRIDAY AND DECREASING TO 1.5 INCHES BY
SATURDAY. EXPECT AFTERNOON SHOWERS AND ISOLATED THUNDERSTORMS
FUELED BY DIURNAL HEATING AND LOCAL EFFECTS. AS A RESULT, URBAN
AND SMALL STREAM FLOODING IS LIKELY TO PERSIST EACH DAY, AND SOME
RIVERS MAY REACH FLOOD STAGE. IN THE VIRGIN ISLANDS, PERIODS OF
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO CAUSE WATER SURGES ALONG
GUTS AND DRAINAGE CHANNELS, PONDING ON ROADWAYS, AND ISOLATED
URBAN FLOODING. ADDITIONAL HAZARDS INCLUDE LANDSLIDES, FREQUENT
LIGHTNING, AND GUSTY WINDS.
THIS FORECAST SCENARIO ASSUMES THAT THE CURRENT GUIDANCE REMAINS
CONSISTENT REGARDING THE TROPICAL WAVE BEING MONITORED BY THE
NATIONAL HURRICANE CENTER, WHICH CURRENTLY HAS AN 80% CHANCE OF
FORMATION IN THE NEXT 48 HOURS AND A 90% CHANCE OVER THE NEXT
SEVEN DAYS. IF DEVELOPMENT CONTINUES AS EXPECTED, THE SYSTEM MAY
TRACK NORTHWESTWARD TOWARD THE NORTHEASTERN CARIBBEAN. WE WILL
CONTINUE TO MONITOR THIS CLOSELY AND PROVIDE UPDATES THROUGHOUT
THE WORKWEEK.
SUNDAY THROUGH TUESDAY SHOULD BE THE MORE STABLE DAYS OF THE
FORECAST PERIOD, WITH 500 MB TEMPERATURES WARMING TO ABOVE NORMAL,
AROUND -5 TO -4 DEGREES CELSIUS. DRIER AIR IS FORECAST TO MOVE
INTO THE REGION, WITH BELOW NORMAL PWAT VALUES PERSISTING THROUGH
TUESDAY (1.5 INCHES OR LOWER). RAINFALL ACTIVITY WILL DIMINISH,
BUT LOCALIZED AFTERNOON CONVECTION, PARTICULARLY IN THE WESTERN
SECTORS OF PUERTO RICO, WILL STILL BE POSSIBLE DUE TO LOCAL
EFFECTS AND DIURNAL HEATING. WINDS WILL BE VERY LIGHT, SO SHOWERS
WILL BE VERY SLOW MOVING, AND THE FLOOD RISK WILL REMAIN MOSTLY
LIMITED. BY TUESDAY NIGHT, ANOTHER TROPICAL WAVE IS EXPECTED TO
APPROACH THE AREA, FURTHER INCREASING MOISTURE AND BRINGING BETTER
CHANCES FOR RAIN ONWARD.
IN TERMS OF TEMPERATURES, 925 MB VALUES ARE FORECAST TO PEAK AT
NEARLY TWO STANDARD DEVIATIONS ABOVE NORMAL FROM FRIDAY INTO THE
WEEKEND. THIS PATTERN WILL ELEVATE THE HEAT RISK ACROSS THE
REGION. HEAT ADVISORIES OR EVEN EXTREME HEAT WARNINGS MAY BE
ISSUED. RESIDENTS AND VISITORS ARE STRONGLY ADVISED TO STAY
HYDRATED, AVOID PROLONGED SUN EXPOSURE DURING PEAK HEAT HOURS,
AND TAKE EXTRA PRECAUTIONS, PARTICULARLY THOSE WITHOUT ACCESS TO
ADEQUATE COOLING OR HYDRATION.
AVIATION
(06Z TAFS)
SHRA/TSRA ARE EXPECTED ACROSS THE REGION OVER THE NEXT 48 HOURS,
BRINGING PERIODS OF MVFR TO BRIEF IFR CONDITIONS. ACTIVITY WILL
MAINLY AFFECT TJSJ AND USVI TERMINALS THROUGH 16/16Z, SHIFTING TO
TJBQ AND TJPS THROUGH 16/22Z, THEN RETURNING TO TJSJ AND USVI
TERMINALS AFTER 16/22Z. WINDS WILL BE LIGHT TO CALM AND VARIABLE
EARLY, INCREASING TO 15–20 KTS WITH GUSTS UP TO 25–30 KTS BETWEEN
16/14-22Z, BEFORE DIMINISHING AGAIN TO LIGHT AND VARIABLE AFTER
16/22Z. GUSTY WINDS ARE POSSIBLE NEAR SHRA/TSRA.
MARINE
A SURFACE HIGH PRESSURE SYSTEM LOCATED OVER THE CENTRAL AND EASTERN
ATLANTIC, IN COMBINATION WITH A DEPARTING LOW-LEVEL PERTURBATION,
WILL PROMOTE MODERATE TO LOCALLY FRESH EAST TO NORTHEASTERLY WINDS
TODAY. SMALL CRAFT ARE URGED TO EXERCISE CAUTION ACROSS THE OFFSHORE
WATERS AND LOCAL PASSAGES. PASSING SHOWERS AND ISOLATED THUNDERSTORMS
WILL CONTINUE THROUGH THE MORNING HOURS ACROSS MOST WATERS, FOLLOWED
BY STRONGER THUNDERSTORMS ACROSS THE WESTERN WATERS OF PUERTO RICO
AND THE MONA PASSAGE DURING THE EARLY AFTERNOON HOURS. A STRONGER
TROPICAL WAVE IS EXPECTED TO APPROACH LATE TONIGHT INTO WEDNESDAY,
ENHANCING INTENSITY AND SHOWER COVERAGE.
BEACH FORECAST
TODAY, THERE IS A MODERATE RISK OF RIP CURRENTS ACROSS THE NORTH AND
EAST-FACING BEACHES OF PUERTO RICO, CULEBRA, AND ST. CROIX. SIMILAR
CONDITIONS ARE EXPECTED TO PREVAIL MOST OF THE WORKWEEK SO BEACHGOERS
ARE ADVISED TO EXERCISE CAUTION AT ALL TIMES AS A MODERATE RISK MEANS
LIFE-THREATHERNING RIP CURRENT ARE POSSIBLE IN THE SURF ZONE. A LOW
RISK SHOULD PREVAIL ELSEWHERE. ADDITIONAL HAZARDS INCLUDE AFTERNOON
THUNDERSTORMS. REMEMBER, IF YOU HEAR THUNDER, SEEK SHELTER INSIDE
OF A SAFER PLACE IMMEDIATELY.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY FROM 10 AM THIS MORNING TO 5 PM AST THIS AFTERNOON
FOR PRZ001>005-007-008-010>013.
VI...HEAT ADVISORY FROM 10 AM THIS MORNING TO 5 PM AST THIS AFTERNOON
FOR VIZ001-002.
AM...NONE.
SHORT TERM/AVIATION...ICP
LONG TERM/MARINE/BEACH FORECAST...YZR
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page