642
FXCA62 TJSJ 151758
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
158 PM AST FRI AUG 15 2025
KEY MESSAGES
* HEAVY RAINFALL TONIGHT THROUGH SUNDAY ACROSS THE U.S.
VIRGIN ISLANDS AND PUERTO RICO MAY LEAD TO ISOLATED TO LOCALLY
FLASH AND URBAN FLOODING, ALONG WITH LANDSLIDES OR MUDSLIDES.
* GUSTS TO TROPICAL STORM FORCE ARE POSSIBLE IN RAINBANDS OVER
PORTIONS OF THE U.S. VIRGIN ISLANDS AND PUERTO RICO DURING THE
WEEKEND.
* MARINE AND COASTAL CONDITIONS WILL DETERIORATED AS HURRICANE
ERIN MOVES CLOSER TO THE FORECAST AREA.
SHORT TERM...TONIGHT THROUGH SUNDAY
WEATHER CONDITIONS REMAINED RELATIVELY CALM ACROSS PUERTO RICO AND
THE U.S. VIRGIN ISLANDS DURING THE EARLY PART OF THE DAY. DURING
THE LATE MORNING, SHOWERS BEGAN TO DEVELOP OVER EASTERN AND
SOUTHWESTERN PUERTO RICO, AS WELL AS CULEBRA AND VIEQUES,
PRODUCING BETWEEN 0.10 AND 0.50 INCHES OF RAINFALL. BY THE AFTERNOON,
SHOWERS AND THUNDERSTORMS FORMED OVER THE SOUTHWESTERN PORTIONS
OF THE CORDILLERA CENTRAL. TEMPERATURES RANGED FROM THE UPPER 80S
TO LOW 90S ALONG THE COASTAL AREAS OF PUERTO RICO AND THE U.S.
VIRGIN ISLANDS, AND FROM THE UPPER 70S TO UPPER 80S IN THE
MOUNTAINS. HEAT INDICES REACHED 100 DEGREES FAHRENHEIT IN SOME
URBAN AND COASTAL LOCATIONS. WINDS WERE GENERALLY FROM THE
NORTHEAST, SHIFTING AT TIMES TO VARIABLE DIRECTIONS, AS HURRICANE
ERIN CONTINUED TO APPROACH THE REGION.
AS MENTIONED IN PREVIOUS DISCUSSIONS, THERE WILL BE A GRADUAL INCREASE
IN WET AND UNSTABLE WEATHER CONDITIONS OVER THE COMING DAYS, WITH
RAINFALL AMOUNTS POTENTIALLY EXCEEDING 5 INCHES IN LOCALIZED
AREAS. THEREFORE, A FLOOD WATCH HAS BEEN ISSUED. THAT BEING SAID,
THE OUTER RAINBANDS FROM ERIN ARE EXPECTED TO BEGIN AFFECTING THE
ISLANDS AS EARLY AS LATE TONIGHT OR EARLY SATURDAY MORNING,
IMPACTING NORTHERN AND EASTERN PUERTO RICO, ATLANTIC OFFSHORE
WATERS, THE ANEGADA PASSAGE, AND THE U.S. VIRGIN ISLANDS. THESE
BANDS WILL BRING PERIODS OF SQUALLY WEATHER WITH THUNDERSTORMS,
HEAVY RAINFALL, AND GUSTY WINDS BETWEEN 30 AND 40 MPH, WITH HIGHER
GUSTS POSSIBLE. ACTIVITY WILL BECOME MORE FREQUENT AS ERIN
CONTINUES ITS TRAJECTORY TOWARDS THE WEST-NORTHWEST, WITH PEAK
IMPACTS EXPECTED BY EARLY SUNDAY MORNING WHEN IT WILL BE MOVING
NORTHEAST OF THE CARIBBEAN ISLANDS. HOWEVER, DUE TO THE PROXIMITY
OF HURRICANE ERIN, WINDS ARE EXPECTED TO SHIFT FROM THE SOUTH TO
SOUTHWEST ON SUNDAY, DRAWING DEEP TROPICAL MOISTURE OVER THE
REGION. THIS WILL INCREASE THE RISK FOR URBAN FLOODING, LANDSLIDES
IN STEEP TERRAIN, AND RIVER FLOODING.
REGARDLESS OF THE PATH AND INTENSITY OF THE SYSTEM, VISITORS AND
RESIDENTS ARE URGED TO CLOSELY MONITOR UPDATES ON HURRICANE ERIN,
AS LOCAL WEATHER CONDITIONS WILL BE DIRECTLY INFLUENCED.
LONG TERM...MONDAY THROUGH FRIDAY
//FROM PREVIOUS DISCUSSION//
SOME CHANGES WERE INTRODUCED TO THE LONG-TERM FORECAST, INCREASING
UNCERTAINTY FOR THE SECOND PART OF THE NEXT WORKWEEK. THE LATEST
PROBABILISTIC GUIDANCE OF THE GFS AND ECMWF SHOWS AGREEMENT OF
PRECIPITABLE WATER VALUES REMAINING ABOVE THE 75TH PERCENTILE (2.0 -
2.2 INCHES), DUE TO POSSIBLE TROPICAL MOISTURE POOLED BY TROPICAL
STORM ERIN. AS MENTIONED IN THE PREVIOUS DISCUSSION, THE MAIN AREAS
OF CONCERN ARE THE INTERIOR AND NORTHERN PORTION OF PUERTO RICO AND
THE U.S. VIRGIN ISLANDS DUE TO S-SE WIND FLOW COMBINED WITH DIURNAL
HEATING AND LOCAL EFFECTS. ADDITIONALLY, PREVIOUS RAINFALL ACTIVITY
AND SATURATED SOILS COULD ENHANCE THE POTENTIAL OF URBAN FLOODING,
LANDSLIDES, AND RIVER RISES OVER THE AFOREMENTIONED AREAS. ONCE
AGAIN, THE FLOODING RISK WILL REMAIN LIMITED TO ELEVATED FOR MOST
PORTIONS OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS. RESIDENTS AND
VISITORS SHOULD CONTINUE TO MONITOR THE SYSTEM AND STAY TUNED FOR
FURTHER UPDATES.
MOISTURE CONTENT IS EXPECTED TO GRADUALLY DECREASE BY WEDNESDAY AS
ERIN MIGRATES NORTHEASTWARD INTO THE WESTERN CARIBBEAN BASED ON THE
LATEST NHC ADVISORY. A SURFACE HIGH PRESSURE SHOULD SETTLE JUST
NORTHEAST OF THE CWA AND LINGER FOR THE NEXT FEW DAYS, PROMOTING
WINDS FROM THE SOUTHEAST. AN UPPER-LEVEL TROUGH SHOULD APPROACH THE
LOCAL AREA, INCREASING MOISTURE CONTENT, COOLING 500 MB TEMPERATURES
AND INCREASING INSTABILITY ALOFT. NEVERTHELESS, THERE’S SOME
UNCERTAINTY INTRODUCED TO THE FORECAST, MAINLY FOR FRIDAY, DUE TO
ANOTHER TROPICAL WAVE APPROACHING THE CARIBBEAN BASIN, ALTHOUGH
THERE ARE SOME DISCREPANCIES. THE GFS 06Z SOLUTION SHOWS A POTENTIAL
TROPICAL CYCLONE MOVING ACROSS THE CENTRAL ATLANTIC, TURNING NORTH
BEFORE APPROACHING THE CWA , WHILE THE ECMWF 00Z SOLUTION SHOWS
THIS DISTURBANCE APPROACHING THE LOCAL AREA. BASED ON THE
DETERMINISTIC GUIDANCE, THE GRAND ENSEMBLE SHOWS A GRADUAL
INCREASE IN MOISTURE CONTENT, BUT THERE IS HIGH VARIABILITY IN
PWAT VALUES DURING THAT TIME PERIOD. SINCE THESE CONDITIONS ARE
EXPECTED AT THE END OF THE FORECAST PERIOD, UNCERTAINTY REMAINS
HIGH, AND CHANGES TO THE FORECAST WILL CONTINUE FOR THE NEXT FEW
DAYS.
IF THE WIND FLOW REMAINS WITH A SOUTHERLY COMPONENT, ABUNDANT
MOISTURE CONTENT, AND ABOVE CLIMATOLOGICAL NORMAL 925 MB
TEMPERATURES, THE HEAT RISK WILL LIKELY CONTINUE LIMITED TO ELEVATED
ACROSS URBAN AND COASTAL AREAS OF PUERTO RICO AND THE U.S. VIRGIN
ISLANDS DURING THE LONG-TERM FORECAST. TUESDAY AND WEDNESDAY ARE
LIKELY TO BE THE HOTTEST DAYS OF THE PERIOD, WITH HEAT INDEXES
MEETING HEAT ADVISORY CRITERIA.
AVIATION
(18Z TAFS)
SHRA/TSRA ASSOCIATED TO THE RAINBANDS FROM HURRICANE ERIN WILL GRADUALLY
INCREASE IN A NE WIND FLOW THRU AT LEAST 16/02Z, WINDS WILL THEN ACQUIRE A NNE
TO N COMPONENT THROUGH THE NIGHT. MVFR TO IFR CONDS ARE EXPECTED AFT 15/23Z
THRU THE PERIOD, STARTING ACROSS THE USVI TERMINALS AND SPREADING ACROSS THE
EASTERN PR TERMINALS. NNE-NE WINDS SHOULD PREVAIL BTW 10-15 KT WITH GUSTS UP TO
30 KT, TURNING NNE TO NNW AFT 16/17Z. GUSTS WILL BE MORE PREVALENT WITHIN
SHRA/TSRA.
MARINE
THE FORECAST REMAINS ON TRACK, ALTHOUGH SMALL CRAFT ADVISORIES HAVE BEEN
REISSUED NOW STARTING SATURDAY MORNING, WITH THE INCLUSION OF THE OFFSHORE
CARIBBEAN WATERS. THERE IS AN INCREASED POTENTIAL FOR STRONG SHOWERS AND
THUNDERSTORMS, ALONG WITH GUSTY WINDS, AS OUTER BANDS FROM ERIN MOVE OVER THE
EASTERN AND NORTHERN WATERS. WINDS OF 25–30 KNOTS, OR EVEN HIGHER, ARE
POSSIBLE, PARTICULARLY ACROSS THE OFFSHORE ATLANTIC WATERS.
BEACH FORECAST
SWELL ACTION FROM ERIN WILL RESULT IN LARGE BREAKING WAVES, CREATING DANGEROUS
SWIMMING CONDITIONS AND POTENTIAL MINOR BEACH EROSION, PARTICULARLY ALONG
NORTHERN AND EASTERN EXPOSED BEACHES. AS A RESULT, HIGH RIP CURRENT RISK AND
HIGH SURF ADVISORIES WILL BE IN EFFECT FROM SATURDAY THROUGH AT LEAST
LATE SUNDAY NIGHT. IN ADDITION, OUTER BANDS FROM ERIN WILL BRING
PERIODS OF HEAVY SHOWERS, FREQUENT LIGHTNING, AND GUSTY WINDS, MAKING
OUTDOOR ACTIVITIES POTENTIALLY HAZARDOUS WITH CONDITIONS DETERIORATING
QUICKLY.
SJU WATCHES/WARNINGS/ADVISORIES
PR...FLOOD WATCH FROM MIDNIGHT AST TONIGHT THROUGH MONDAY EVENING FOR
PRZ001>013.
HIGH RIP CURRENT RISK FROM SATURDAY MORNING THROUGH LATE SUNDAY
NIGHT FOR PRZ001-002-005-008-010-012-013.
HIGH SURF ADVISORY FROM 8 AM SATURDAY TO 6 AM AST MONDAY FOR
PRZ001-002-005-008-012-013.
VI...FLOOD WATCH FROM MIDNIGHT AST TONIGHT THROUGH MONDAY EVENING FOR
VIZ001-002.
HIGH RIP CURRENT RISK FROM SATURDAY MORNING THROUGH LATE SUNDAY
NIGHT FOR VIZ001-002.
HIGH SURF ADVISORY FROM 8 AM SATURDAY TO 6 AM AST MONDAY FOR
VIZ001-002.
AM...SMALL CRAFT ADVISORY FROM 8 AM SATURDAY TO 6 AM AST MONDAY FOR
AMZ711-723.
SMALL CRAFT ADVISORY FROM 6 PM SATURDAY TO 6 AM AST MONDAY FOR
AMZ712-716-726-733.
SHORT TERM...MMC
LONG TERM...MNG
AVIATION/MARINE/BEACH FORECAST...CVB
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