941
FXCA62 TJSJ 130745
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
345 AM AST SAT DEC 13 2025
..NEW SHORT TERM, LONG TERM, AVIATION
KEY MESSAGES
ISSUED AT 304 AM AST SAT DEC 13 2025
* CHOPPY TO ROUGH SEAS AND LIFE-THREATENING RIP CURRENTS ARE
EXPECTED TO CONTINUE THROUGH THE WEEKEND ACROSS PUERTO RICO AND
THE U.S. VIRGIN ISLANDS.
* PATCHES OF MOISTURE WILL CONTINUE TO REACH THE ISLANDS TODAY
INTO SUNDAY, INCREASING PASSING SHOWER ACTIVITY. LIMITED
AFTERNOON CONVECTION POSSIBLE OVER NORTHWEST PR.
* FOR THE U.S. VIRGIN ISLANDS, PASSING SHOWERS DRAGGED BY THE
TRADE WINDS WILL CONTINUE TO MOVE INTO THE AREA TODAY.
* BREEZY TO LOCALLY WINDY CONDITIONS ARE EXPECTED ACROSS THE
ISLANDS THIS WEEKEND.
SHORT TERM(TODAY THROUGH MONDAY)
ISSUED AT 304 AM AST SAT DEC 13 2025
TODAY IS EXPECTED TO BE THE WETTEST DAY OF THE SHORT TERM PERIOD DUE
TO A SURGE OF MOISTURE ASSOCIATED WITH A WEAK TRADE WIND TROUGH.
THIS INCREASE IN MOISTURE CONTENT, COMBINED WITH DAYTIME HEATING AND
OROGRAPHIC LIFT OVER THE CORDILLERA CENTRAL, COULD LEAD TO SCATTERED
TO LOCALLY NUMEROUS SHOWERS, OVER CENTRAL AND WESTERN PR. HOWEVER, A
WETTER PATTERN IS EXPECTED LATE THIS AFTERNOON AND THROUGH TONIGHT
ACROSS THE USVI AND MOST COASTAL AREAS NORTHERN AND SOUTHERN PR, AS
WELL ACROSS THE EASTERN HALF OF PR AS THE TROUGH CROSSES THE LOCAL
AREA. THE PRECIPITABLE WATER CONTENT IS EXPECTED TO PEAK CLOSE TO 2
INCHES, WELL ABOVE NORMAL LEVELS. ISOLATED THUNDERSTORMS CANNOT BE
RULED OUT, SPECIALLY IN AN ADVECTIVE PATTERN ACROSS THE WATERS
BETWEEN THE USVI AND EASTERN PR. URBAN AND SMALL STREAM FLOODING IS
EXPECTED WITH THE TROUGH PASSAGE.
IN CONTRAST, ON SUNDAY A TEMPORARY BREAK FROM THE RAIN IS EXPECTED
AS A POCKET OF DRIER AND MORE STABLE AIR MOVES IN FROM THE EAST.
BASED ON GLOBAL GUIDANCE, THIS IS EVIDENCED BY A SIGNIFICANT DROP IN
COLUMNAR MOISTURE, WITH 850-700MB RELATIVE HUMIDITY LEVELS DROPPING
FROM NEAR 50% TODAY TO 10% ON SUNDAY, RESULTING IN MOSTLY SUNNY
CONDITIONS WITH ONLY ISOLATED SHOWERS(0-20%). HOWEVER, THIS DRIER
PHASE WILL BE SHORT LIVED. AS AN INCREASE IN WIND SPEEDS AND A
SUBSEQUENT RETURN TO HIGHER MID-LEVEL MOISTURE CONTENT IS FORECAST
BETWEEN LATE SUNDAY NIGHT INTO MONDAY. THIS SUGGESTS THAT SCATTERED
SHOWERS(30-50%) WILL BECOME MORE LIKELY AGAIN AS THE SYNOPTIC
PATTERN INFLUENCED BY A PRE-FRONTAL TROUGH SHIFTS BACK TO A MORE
FAVORABLE SETUP FOR RAINFALL.
LONG TERM(TUESDAY THROUGH SATURDAY)
ISSUED AT 304 AM AST SAT DEC 13 2025
THE APPROACH OF A FRONTAL SYSTEM AND ITS ASSOCIATED UPPER-LEVEL
TROUGH OVER THE WESTERN ATLANTIC WILL PROMOTE UNSTABLE CONDITIONS
DURING THE FIRST HALF OF THE LONG TERM PERIOD. NORMAL TO SLIGHTLY
ABOVE-NORMAL PRECIPITABLE WATER CONTENT (PWAT) OF 1.75 TO 1.90
INCHES WILL ENHANCE THE POTENTIAL FOR SHOWER DEVELOPMENT ACROSS THE
REGION. SHOWERS ARE MOST LIKELY OVER PORTIONS OF EASTERN PUERTO RICO
AND THE U.S. VIRGIN ISLANDS DURING THE OVERNIGHT AND MORNING HOURS,
FOLLOWED BY AFTERNOON SHOWERS OVER PORTIONS OF CENTRAL AND WESTERN
PUERTO RICO. DURING THIS PERIOD, THE 500 MB TEMPERATURES ARE
EXPECTED TO DROP INTO THE -6C TO -7C RANGE, MEANING THE POTENTIAL
FOR AFTERNOON THUNDERSTORMS, PARTICULARLY ACROSS WESTERN PUERTO
RICO, CANNOT BE RULED OUT.
AT THE SURFACE, A STRONG HIGH-PRESSURE SYSTEM LOCATED OVER THE
CENTRAL ATLANTIC WILL MAINTAIN AN EAST-SOUTHEASTERLY WIND FLOW
ACROSS THE AREA, PROMOTING SLIGHTLY HIGHER THAN NORMAL TEMPERATURES
THROUGHOUT THE WEEK. HOWEVER, BY THE SECOND HALF OF THE LONG-TERM
PERIOD, ANOTHER HIGH-PRESSURE SYSTEM IS EXPECTED TO BUILD OVER THE
WESTERN ATLANTIC BEHIND THE FRONTAL SYSTEM. BY THEN, WINDS ARE
EXPECTED TO SHIFT FROM THE NORTHEAST, LEADING TO COOLER TEMPERATURES
INTO THE NORTHEASTERN CARIBBEAN REGION.
AVIATION
(06Z TAFS)
ISSUED AT 304 AM AST SAT DEC 13 2025
VFR CONDITIONS EARLY IN THE PERIOD. HOWEVER, SHRA WITH MAX TOPS
AROUND 15 KFT ARE EXPECTED TO CONTINUE TO MOVE FROM THE ANEGADA
PASSAGE, AND CAUSE MOSTLY -RA/VCSH ACROSS THE USVI AND EASTERN PR
TERMINALS EARLY THIS MORNING. LATE THIS EVENING AND THROUGH THE
OVERNIGHT HOURS, ADDITIONAL SHRA EN ROUTE FROM THE LEEWARD ISLANDS
ASSOCIATED TO A WEAK SURFACE TROUGH COULD LEAD TO TEMPO MVFR TO
BRIEF IFR CONDS ACROSS THE SAME TERMINALS. ISO TSRA IS POSSIBLE,
PARTICULARLY BTW 14/00Z-06Z. EAST WINDS EXPECTED TO INCREASE BETWEEN
15 AND 20 KT WITH SEA BREEZE VARIATIONS AND STRONGER GUSTS AFT
13/14Z.
MARINE
ISSUED AT 304 AM AST SAT DEC 13 2025
A SURFACE HIGH PRESSURE SYSTEM WILL CONTINUE TO BUILD NEAR THE
AZORES THROUGH THE WEEKEND. A WEAK COLD FRONT AND ANOTHER SURFACE
HIGH PRESSURE SYSTEM WILL MOVE FROM THE WESTERN ATLANTIC INTO THE
CENTRAL ATLANTIC OVER THE NEXT FEW DAYS. THIS PATTERN WILL PROMOTE
MODERATE TO LOCALLY FRESH EAST TO SOUTHEAST TRADE WINDS ACROSS
THE LOCAL WATERS. INCREASING WINDS AND A LONG-PERIOD NORTHERLY
SWELL WILL RESULT IN CHOPPY TO ROUGH SEAS, MAINLY ACROSS THE
ATLANTIC WATERS AND PORTIONS OF THE ANEGADA AND MONA PASSAGES.
SMALL CRAFT ADVISORIES REMAIN IN EFFECT AT LEAST THROUGH TOMORROW
MORNING ACROSS THE PASSAGES AND THROUGH SUNDAY AFTERNOON ACROSS
THE OFFSHORE ATLANTIC WATERS.
BEACH FORECAST
ISSUED AT 304 AM AST SAT DEC 13 2025
A LONG-PERIOD NORTHERLY SWELL AND INCREASING WIND WAVES WILL
CREATE LIFE-THREATENING RIP CURRENTS ALONG THE NORTH AND EAST
FACING BEACHES OF THE ISLANDS OVER THE NEXT FEW DAYS. A RIP
CURRENT STATEMENT REMAINS IN EFFECT FOR THE NORTHWEST TO NORTHEAST
BEACHES OF PUERTO RICO, INCLUDING CULEBRA, AS WELL AS ST. THOMAS
AND ST. JOHN. BEACHGOERS ARE URGED TO AVOID SWIMMING IN THESE
CONDITIONS, PARTICULARLY THROUGH LATE TONIGHT. THE WEST AND
SOUTH- FACING BEACHES OF THE ISLANDS WILL EXPERIENCE A MODERATE
RISK OF RIP CURRENTS. FOR SPECIFIC LOCATION INFORMATION, PLEASE
VISIT WEATHER.GOV/BEACH/SJU.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HIGH RIP CURRENT RISK THROUGH LATE TONIGHT FOR PRZ001-002-005-
008.
HIGH RIP CURRENT RISK THROUGH THIS AFTERNOON FOR PRZ012.
VI...HIGH RIP CURRENT RISK UNTIL 6 AM AST EARLY THIS MORNING FOR
VIZ001.
HIGH RIP CURRENT RISK THROUGH THIS AFTERNOON FOR VIZ002.
AM...SMALL CRAFT ADVISORY UNTIL 5 PM AST SUNDAY FOR AMZ711.
SMALL CRAFT ADVISORY UNTIL NOON AST TODAY FOR AMZ723.
MIDNIGHT CREW...DSR/GRS
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