989
FXCA62 TJSJ 181740
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
140 PM AST THU SEP 18 2025
KEY MESSAGES
* ACROSS THE U.S. VIRGIN ISLANDS, A SHOWERY PATTERN WILL CONTINUE
THROUGH EARLY THIS EVENING, ENHANCING THE FLOOD POTENTIAL.
* A WARMING TREND IS EXPECTED TO BEGIN ON FRIDAY, BRINGING
INCREASING TEMPERATURES THAT MAY CAUSE HEAT INDICES TO REACH
HEAT ADVISORY OR EXTREME HEAT WARNING CRITERIA THROUGH AT LEAST
EARLY NEXT WEEK, PARTICULARLY IN COASTAL AND URBAN AREAS.
* SWELLS FROM TROPICAL STORM GABRIELLE WILL MOVE ACROSS THE LOCAL
WATERS DURING THE WEEKEND, INCREASING THE POTENTIAL FOR LIFE-
THREATENING RIP CURRENTS ACROSS THE NORTH AND EAST FACING
BEACHES OF THE ISLANDS. SEAS ARE EXPECTED TO REMAIN BELOW SMALL
CRAFT ADVISORY CRITERIA.
SHORT TERM...REST OF TODAY THROUGH SATURDAY
AN ELONGATED INDUCED LOW-LEVEL TROUGH OVER THE LOCAL AREA PRODUCED
PERSISTENT RAINFALL ACROSS THE U.S. VIRGIN ISLANDS AND PORTIONS OF
EASTERN PUERTO RICO DURING THE PAST 8-12 HOURS. OBSERVED RAINFALL
AMOUNTS UP TO 6 INCHES WERE REPORTED IN ST. CROIX AND UP TO 4
INCHES IN LAS PIEDRAS AND HUMACAO. BY NOON, HIGH TEMPERATURES
WERE IN THE LOW 80S ACROSS MOST LOWER ELEVATIONS OF THE ISLANDS,
EXCEPT IN WESTERN PR, WHERE TEMPERATURES WERE IN THE MID-80S TO
LOW 90S. WINDS WERE LIGHT WITH A SOUTHERLY COMPONENT, AND SEA
BREEZE VARIATIONS IN NORTHWESTERN PR.
FOR THE REST OF THE AFTERNOON HOURS, ADDITIONAL SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO REDEVELOP ACROSS THE CARIBBEAN
WATERS, AND UNDER SOUTHERLY STEERING WINDS MOVE AGAIN OVER
PORTIONS OF THE USVI. THEREFORE, FLOODING CONCERNS WILL CONTINUE
ACROSS THE USVI TERRITORIES, PARTICULARLY IN ST. CROIX. ACROSS PR,
THE INTERACTION OF THE INDUCED TROUGH AND THE ABUNDANT TROPICAL
MOISTURE WILL PRODUCE SCATTERED TO LOCALLY NUMEROUS SHOWERS,
MAINLY OVER WESTERN PR, WHILE THE EASTERN HALF OF PR WILL CONTINUE
TO EXPERIMENT PERIODS OF STRATIFORM RAIN TO POSSIBLE HEAVY SHOWERS
FROM THIS EVENING THROUGH AT LEAST FRIDAY MORNING.
FOR THE REST OF THE FORECAST PERIOD, THE PROXIMITY OF AN UPPER-
LEVEL LOW TO OUR NORTH AND THE INDUCED LOW-LEVEL TROUGH TO OUR
WEST WILL CONTINUE TO PROMOTE AN UNSTABLE WEATHER PATTERN ACROSS
THE REGION. MEANWHILE, A LIGHT SOUTHERLY WIND FLOW IS EXPECTED TO
PREVAIL, AND HEAT ADVISORY TO EXTREME HEAT WARNING CONDITIONS ARE
EXPECTED TO RETURN ONCE AGAIN ACROSS MOST COASTAL AREAS OF THE
ISLANDS, AND BEFORE THE ONSET OF AFTERNOON CONVECTION EACH DAY.
LONG TERM...SUNDAY THROUGH THURSDAY
FOR THE LONG-TERM PERIOD, AS TROPICAL STORM GABRIELLE MOVES WELL
NORTHEAST OF THE REGION, OUR AREA WILL BE POSITIONED IN A COL
REGION. AS THE PRESSURE GRADIENT WEAKENS, VERY LIGHT EAST-
SOUTHEASTERLY WINDS ARE EXPECTED TO PERSIST ON SUNDAY AND CONTINUE
THROUGH AT LEAST MONDAY NIGHT. THIS FLOW WILL HELP MAINTAIN A
HEALTHY MOISTURE CONTENT ACROSS THE AREA. ACCORDING TO THE LATEST
MODEL GUIDANCE, PRECIPITABLE WATER VALUES ARE FORECAST TO
FLUCTUATE BETWEEN 1.80 AND 2.20 INCHES FROM SUNDAY THROUGH
TUESDAY, WHICH IS WITHIN THE AVERAGE TO ABOVE-AVERAGE RANGE FOR
THIS TIME OF YEAR. IN TERMS OF TEMPERATURE, FORECAST DATA
SUGGESTS THAT 925 MB TEMPERATURES WILL PEAK AT NEARLY TWO STANDARD
DEVIATIONS ABOVE NORMAL ON SUNDAY AND REMAIN NEAR THE 75TH
PERCENTILE INTO EARLY NEXT WEEK. THIS PATTERN WILL INCREASE THE
RISK OF HEAT-RELATED IMPACTS ACROSS THE REGION. HEAT ADVISORIES OR
EVEN EXTREME HEAT WARNINGS MAY BE ISSUED.
UNDER THIS SCENARIO, EXPECT MORNING SHOWERS ACROSS WINDWARD AREAS
OF THE ISLANDS, FOLLOWED BY AFTERNOON SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS THE INTERIOR AND WESTERN SECTORS OF PUERTO
RICO, FUELED BY DIURNAL HEATING AND LOCAL EFFECTS. URBAN AND SMALL
STREAM FLOODING IS LIKELY TO PERSIST EACH DAY, AND SOME RIVERS
MAY REACH FLOOD STAGE. SATURATED SOILS FROM RECENT RAINFALL
COMBINED WITH LIGHT WINDS DURING THIS PERIOD WILL CONTRIBUTE TO
SLOWER-MOVING SHOWERS, WHICH COULD LEAD TO HIGHER RAINFALL TOTALS
AND AN INCREASED RISK OF FLOODING. ADDITIONAL HAZARDS MAY INCLUDE
LANDSLIDES, FREQUENT LIGHTNING, AND GUSTY WINDS.
ON TUESDAY NIGHT, A WIND SURGE IS EXPECTED TO APPROACH THE REGION,
BRINGING GUSTY WINDS ALONG WITH INCREASED MOISTURE AND A HIGHER
CHANCE OF RAINFALL THROUGH THE MIDDLE OF THE WEEK. BY WEDNESDAY
AND THURSDAY, ONE OF THE TROPICAL WAVES CURRENTLY BEING MONITORED
BY THE NATIONAL HURRICANE CENTER IS EXPECTED TO APPROACH, FURTHER
ENHANCING A WETTER PATTERN ACROSS THE ISLANDS. WE WILL CONTINUE TO
MONITOR THIS EVOLVING SITUATION CLOSELY AND PROVIDE UPDATES AS
NECESSARY.
AVIATION
(12Z TAFS)
SHRA/TSRA IN AND AROUND THE USVI TERMINALS WILL CONTINUE TO CAUSE
TEMPO MVFR TO BRIEF IFR CONDS THRU AT LEAST 18/22Z. ACROSS THE PR
TERMINALS, MOSTLY -RA EXPECTED WITH MTN TOPS OBSCD AND BKN/OVC
LYRS FM FL060-FL100. THE 18/12Z TJSJ SOUNDING INDICATED SE WINDS
UP TO 13 KT BLO FL080.
MARINE
A WEAK SURFACE HIGH-PRESSURE OVER THE CENTRAL ATLANTIC WILL
PROMOTE LIGHT TO LOCALLY MODERATE EAST TO SOUTHEAST WINDS TODAY.
FOR THE REST OF THE FORECAST PERIOD, LIGHTER SOUTHEASTERLY WINDS
WILL PREVAIL AS THE LOCAL PRESSURE GRADIENT WEAKENS. HIGH MOISTURE
CONTENT FROM A DEPARTING TROPICAL WAVE AND AN INDUCED TROUGH WILL
CONTINUE TO RESULT IN FREQUENT SHOWERS AND STRONG THUNDERSTORMS
OVER THE LOCAL WATERS THROUGH TONIGHT. A LONG PERIOD NORTHEASTERLY
SWELL GENERATED BY TROPICAL STORM GABRIELLE WILL REACH THE LOCAL
WATERS AND PASSAGES DURING THE WEEKEND. HOWEVER, SEAS ARE FORECAST
TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA.
BEACH FORECAST
THERE IS A MODERATE RISK OF RIP CURRENTS FOR THE NORTH AND EAST-
FACING BEACHES OF PUERTO RICO, CULEBRA, AND ST. CROIX, WITH A LOW
RISK ELSEWHERE. WHILE A BRIEF IMPROVEMENT IN CONDITIONS IS
EXPECTED ON FRIDAY, THE MODERATE RISK WILL RETURN SATURDAY AND
PERSIST INTO EARLY NEXT WEEK, DRIVEN BY SWELLS FROM TROPICAL STORM
GABRIELLE. HOWEVER, BEACHGOERS SHOULD EXERCISE CAUTION AT ALL
TIMES, DUE TO THE INCREASING THREAT OF LIFE-THREATENING RIP
CURRENTS.
IN ADDITION, AFTERNOON THUNDERSTORMS PRODUCING CLOUD TO GROUND
LIGHTNING ARE EXPECTED EACH DAY, MAINLY ACROSS THE NORTH AND
WESTERN COASTAL AREAS OF PR. REMEMBER, IF YOU HEAR THUNDER, SEEK
SHELTER IN A SAFE INDOOR LOCATION IMMEDIATELY.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM...DSR
LONG TERM....YZR
AVIATION...DSR
BEACH/MARINE...DSR
PUBLIC...LIS/MNG
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