022
FXCA62 TJSJ 141830
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
230 PM AST SUN SEP 14 2025
KEY MESSAGES
* A TROPICAL WAVE IS CURRENTLY MOVING OVER THE ISLANDS. A TRADE
WIND PERTURBATION, ANOTHER TROPICAL WAVE, AND A TUTT LOW WILL
INCREASE THE FREQUENCY OF SHOWERS AND THUNDERSTORMS THROUGH MUCH
OF THE WORKWEEK. THIS WILL KEEP THE RISK OF FLOODING ELEVATED.
ADDITIONAL THREATS INCLUDE RAPID RIVER RISES, LANDSLIDES, AND
FREQUENT LIGHTNING.
* THE VIRGIN ISLANDS WILL ALSO SEE AN INCREASE IN SHOWERS AND
THUNDERSTORMS, WITH WATER SURGES ALONG THE DRAINAGE GUTS,
PONDING OF WATER ON ROADWAYS, AND OCCASIONAL LIGHTNING AND
LANDSLIDES.
* LATER IN THE WEEK AND INTO NEXT WEEKEND INCREASED HEAT RISKS ARE
FORECAST AGAIN FOR PUERTO RICO AND THE VIRGIN ISLANDS. THIS IS
DEPENDENT ON THE DEVELOPMENT OF A TROPICAL WAVE OVER THE EASTERN
TROPICAL ATLANTIC, CURRENTLY BEING MONITORED BY THE NHC AND
GIVEN A HIGH FORMATION CHANCE IN THE NEXT 7 DAYS.
* A MODERATE RISK OF RIP CURRENTS IS IN EFFECT FOR BEACHES OF
CULEBRA AND ST. CROIX. THIS MODERATE RISK OF RIP CURRENTS IS
FORECAST TO SPREAD TO NORTHERN BEACHES OF PUERTO RICO TONIGHT.
SIMILAR CONDITIONS EXPECTED THROUGH AT LEAST MIDWEEK.
SHORT TERM...REST OF THE AFTERNOON THROUGH TUESDAY
THROUGHOUT THE MORNING HOURS, WEATHER CONDITIONS REMAINED MOSTLY
CALM WITH A FEW SHOWERS MOVING INLAND FROM THE SURROUNDING WATERS
DESPITE THE PRESENCE OF A TROPICAL WAVE IN THE VICINITY. SATELLITE
IMAGERY SHOWED THAT THE MOST ACTIVE PORTION OF THE WAVE WAS LOCATED
SOUTH OF ST. CROIX. BY MIDDAY, SHOWERS AND ISOLATED THUNDERSTORMS
BEGAN TO INCREASE IN FREQUENCY WHILE MOVING NORTHWEST UNDER A
SOUTHEASTERLY WIND FLOW. THESE SHOWERS AND THUNDERSTORMS WERE MOVING
FASTER THAN ON PREVIOUS DAYS, AS INDICATED BY THE 14/12Z TJSJ
SOUNDING, WHICH SHOWED SOUTHEASTERLY STEERING WINDS AT 10–15 KNOTS.
THEREFORE, ALTHOUGH SHOWER AND THUNDERSTORM COVERAGE IS INCREASING,
THEIR QUICKER MOVEMENT WILL LIMIT OVERALL RAINFALL ACCUMULATIONS.
HOWEVER, AS THE TROPICAL WAVE CROSSES THE REGION, CONVERGENCE OF
SHOWERS AND THUNDERSTORMS OVER INTERIOR AND NORTHWESTERN PUERTO RICO
WILL MAINTAIN AN ELEVATED FLOODING THREAT THROUGH THIS EVENING.
A BREAK IN SHOWER ACTIVITY IS EXPECTED LATE TONIGHT AS A DRY SLOT
MOVES ACROSS THE REGION, WITH PRECIPITABLE WATER VALUES FORECAST TO
DROP TO NEARLY TWO STANDARD DEVIATIONS BELOW NORMAL. THIS DRYING
TREND WILL BE SHORT-LIVED, AS VALUES ARE EXPECTED TO REBOUND RAPIDLY
ABOVE 2.20 INCHES BY LATE MONDAY INTO TUESDAY WITH THE ARRIVAL OF A
TRADE WIND PERTURBATION FROM THE EAST. ALOFT, TROUGHINESS WILL
PERSIST THROUGH THE SHORT-TERM PERIOD, AND MODEL GUIDANCE SUGGESTS
THAT A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) NORTHEAST OF THE
LOCAL ISLANDS WILL DRIFT SOUTHWESTWARD AND APPROACH THE REGION BY
TUESDAY.
THE COMBINATION OF WELL-ABOVE-NORMAL MOISTURE AND FAVORABLE UPPER-
LEVEL DYNAMICS WILL MAINTAIN WET AND UNSTABLE CONDITIONS. DIURNALLY
DRIVEN CONVECTION, ENHANCED BY SEA BREEZE CONVERGENCE AND OROGRAPHIC
LIFTING, WILL GENERATE AFTERNOON SHOWERS AND THUNDERSTORMS,
PARTICULARLY ACROSS THE INTERIOR AND NORTHWESTERN PUERTO RICO.
DURING THE NIGHTTIME, ACTIVITY WILL CLUSTER MOSTLY OVER THE WATERS,
ESPECIALLY NEAR THE TUTT NORTHEAST OF THE AREA, WITH SOME OF THIS
ACTIVITY BRUSHING WINDWARD COASTAL REGIONS. HOWEVER, THESE WILL BE
LESS INTENSE AND MORE LOCALIZED THAN THE AFTERNOON CONVECTION. A
LIMITED TO ELEVATED FLOODING THREAT WILL PERSIST DUE TO SATURATED
SOILS AND RIVERS RUNNING AT OR ABOVE NORMAL LEVELS. LOCALIZED FLASH
FLOODING AND LANDSLIDES IN AREAS OF STEEP TERRAIN CANNOT BE RULED
OUT. THUNDERSTORMS WILL ALSO BRING FREQUENT LIGHTNING AND GUSTY WIND
CONDITIONS.
THE HEAT THREAT WILL ALSO CONTINUE THROUGH THE PERIOD. WHILE HEAT
INDEX VALUES ARE NOT EXPECTED TO REACH HEAT ADVISORY CRITERIA, THEY
WILL EXCEED 100F ACROSS COASTAL AND URBAN AREAS. THIS LEVEL OF HEAT
WILL REMAIN A CONCERN FOR VULNERABLE POPULATIONS, PARTICULARLY
INDIVIDUALS OUTDOORS WITHOUT ADEQUATE HYDRATION OR COOLING.
LONG TERM...WEDNESDAY THROUGH SUNDAY
/FROM PREV DISCUSSION
ISSUED AT 337 AM AST SUN SEP 14 2025/
A TROPICAL WAVE CROSSING PUERTO RICO AND THE VIRGIN ISLANDS, ALONG
WITH AN UPPER LEVEL TROUGH WILL MAINTAIN UNSETTLED WEATHER
CONDITIONS THROUGH THURSDAY. PRECIPITABLE WATER VALUES ARE EXPECTED
TO BE AT 2.0 TO 2.25 INCHES, WHICH IS ABOUT ONE STANDARD DEVIATIONS
ABOVE NORMAL FOR MID-SEPTEMBER. THESE FEATURES WILL MAINTAIN THE
PROBABILITY OF PRECIPITATION ON THE HIGH SIDE. SINCE AFTERNOONS HAVE
BEEN SO ACTIVE, SOILS ARE ALREADY SATURATED AND RIVERS ARE RUNNING
HIGH, ESPECIALLY ALONG THE INTERIOR AND WESTERN PUERTO RICO.
THEREFORE, IT IS VERY LIKELY THAT URBAN AND SMALL STREAM FLOODING
WILL CONTINUE EACH DAY. ALSO, RIVERS MAY REACH FLOOD STAGE TOO,
WHILE LANDSLIDES, LIGHTNING STRIKES AND GUSTY WINDS COULD ALSO
DEVELOP. SHOWERS WILL ALSO REACH EASTERN PUERTO RICO AT TIMES, AND
ALTHOUGH SOILS ARE NOT AS SATURATED, IMPACTS SHOULD BE SIMILAR.
ACROSS THE VIRGIN ISLANDS, PERIODS OF SHOWERS AND THUNDERSTORMS WILL
CAUSE WATER SURGE ALONG GUTS AND DRAINAGE CHANNELS, WITH PONDING OF
WATER ON ROADWAYS AND ISOLATED URBAN FLOOD.
MOVING INTO FRIDAY AND THE WEEKEND, THE ATTENTION SHIFTS TOWARD THE
SYSTEM BEING MONITORED BY THE NATIONAL HURRICANE CENTER. SO FAR, THE
GUIDANCE SHOWS THIS TROPICAL WAVE DEVELOPING AND MOVING TOWARD THE
NORTHWEST BEFORE REACHING THE NORTHEASTERN CARIBBEAN.
AS THE SYSTEM MOVES, IT WILL PUSH SOME DRIER AIR INTO THE ISLANDS,
SO WEATHER CONDITIONS SHOULD IMPROVE, AT LEAST IN TERMS OF RAIN.
THE THING IS THAT ALTHOUGH IT WILL NOT BE AS WET, WINDS SHOULD SHIFT
FROM THE SOUTHEAST, AND 925 MB TEMPERATURE VALUES WILL SOAR, GOING
NEARLY TWO STANDARD DEVIATION ABOVE NORMAL. AS A RESULT, VERY HOT
TEMPERATURES WILL COME BACK, WITH THE LIKELIHOOD OF EXPERIENCING
HEAT ADVISORY OR EXTREME HEAT WARNING CONDITIONS. THIS LEVEL OF HEAT
WILL IMPACT ANYONE WITHOUT EFFECTIVE COOLING OR ADEQUATE HYDRATION.
MARINE
A SURFACE HIGH-PRESSURE LOCATED OVER THE CENTRAL AND EASTERN
ATLANTIC IS INTERACTING WITH A FRONTAL BOUNDARY IN THE WESTERN
ATLANTIC, RESULTING IN LIGHT TO MODERATE EAST-SOUTHEASTERLY WINDS
THROUGH TOMORROW. A TROPICAL WAVE WILL CONTINUE TO MOVE OVER THE
LOCAL WATERS TONIGHT, INCREASING THE LIKELIHOOD OF SHOWERS AND
THUNDERSTORMS. AFTER THE TROPICAL WAVE PASSES, LOCAL WINDS WILL
SHIFT TO MODERATE AND OCCASIONALLY FRESH AS THE HIGH- PRESSURE
TIGHTENS THE LOCAL PRESSURE GRADIENT. ANOTHER TROPICAL WAVE IS
EXPECTED TO MOVE THROUGH THE AREA AROUND TUESDAY.
AVIATION
(18Z TAFS)
AFTERNOON SHRA/TSRA COULD GENERATE MVFR TO BRIEF IFR CONDITIONS
ACROSS TJSJ/TJBQ WITH MTN OBSC THROUGH 14/23Z. VCSH POSSIBLE ACROSS
USVI TERMINALS THROUGHOUT THE PERIOD. ESE WINDS OF 10–16 KNOTS
THROUGH 23Z, WITH SEA BREEZE VARIATIONS AND HIGHER GUSTS,
PARTICULARLY NEAR SHRA/TSRA. WINDS WILL SLOW DOWN, BELOW 10 KNOTS
AFTER 23Z, BUT WILL SPEED UP AFTER 15/14Z, MORE OUT OF THE E AT 10-
15 KTS, WITH STRONGER GUSTS.
BEACH FORECAST
A MODERATE RISK OF RIP CURRENTS IS IN EFFECT FOR BEACHES OF CULEBRA
AND ST. CROIX. THIS MODERATE RISK OF RIP CURRENTS IS FORECAST TO
SPREAD TO NORTHERN BEACHES OF PUERTO RICO TONIGHT. OTHER BEACHES
HAVE A LOW RISK OF RIP CURRENTS. EVEN WITH A LOW RISK, LIFE-
THREATENING RIP CURRENTS CAN STILL OCCUR NEAR GROINS, JETTIES,
REEFS, AND PIERS, SO BEACHGOERS ARE ADVISED TO EXERCISE CAUTION AT
ALL TIMES. SIMILAR CONDITIONS ARE EXPECTED TO PERSIST THROUGH AT
LEAST MIDWEEK. ADDITIONAL HAZARDS INCLUDE: ISOLATED AFTERNOON
THUNDERSTORMS AND A HEAT RISK.
HYDROLOGY
/FROM PREV DISCUSSION
ISSUED AT 337 AM AST SUN SEP 14 2025/
ACTIVE AFTERNOONS HAVE MAINTAINED THE SOILS SATURATED ACROSS MOST OF
THE INTERIOR AND WESTERN HALF OF PUERTO RICO. THESE PERIODS OF HEAVY
RAIN HAVE ALSO MAINTAIN THE RIVERS AT ABOVE NORMAL TO MUCH ABOVE
NORMAL LEVELS. THIS UNSETTLED WEATHER PATTERN IS EXPECTED TO PERSIST
THROUGH MUCH OF THE WORKWEEK, AS MOISTURE REMAINS ABOVE NORMAL DUE
TO A COUPLE OF APPROACHING TROPICAL WAVES.
SINCE SOILS ARE SATURATED, MUCH OF THE PRECIPITATION WILL QUICKLY
BECOME EXCESSIVE RUNOFF, CAUSING URBAN OR FLASH FLOODING, WATER
SURGES ALONG RIVERS, RIVERS GOING ABOVE FLOOD STAGE, AND LANDSLIDES
TOO.
THE RIVERS ACROSS THE EASTERN THIRD OF PUERTO RICO ARE NOT AS FULL,
BUT THESE RIVERS USUALLY REACT MUCH FASTER THAN THE RIVERS IN THE
WEST, HENCE, PERIODS OF HEAVY RAIN WILL LIKELY RESULT IN RAPID RIVER
RISES AS WELL.
FOR THE VIRGIN ISLANDS, PERIODS OF HEAVY RAIN WILL CAUSE WATER
SURGES ALONG DRAINAGE GUTS, AND PONDING OF WATER ON ROADWAYS.
URBAN FLOODING COULD DEVELOP TOO, WHILE LANDSLIDES IN AREAS OF STEEP
TERRAIN CANNOT BE RULED OUT.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM/AVIATION...CVB
LONG TERM/HYDROLOGY...ERG
MARINE/BEACH FORECAST...MRR
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