736
FXCA62 TJSJ 180906
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
506 AM AST THU DEC 18 2025
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 500 AM AST THU DEC 18 2025
* A SUBSIDING NORTHERLY SWELL WILL CONTINUE TO PRODUCE HAZARDOUS
MARINE AND BEACH CONDITIONS TODAY. THE HIGH SURF ADVISORY
REMAINS IN EFFECT ALONG NORTHERN PUERTO RICO AND CULEBRA UNTIL
THIS AFTERNOON, WHILE THE HIGH RISK OF RIP CURRENTS REMAINS IN
EFFECT UNTIL EARLY FRIDAY.
* MARINE AND BEACH CONDITIONS ARE FORECAST TO DETERIORATE AGAIN
FROM SATURDAY AFTERNOON INTO SUNDAY DUE TO STRENGTHENING WINDS
AND ANOTHER NORTHERLY SWELL.
* MOSTLY FAIR WEATHER CONDITIONS DURING THE MORNING ACROSS PR AND
THE USVI, THEN AN APPROACHING PERTURBATION IS EXPECTED TO BRING
A MODERATE CHANCE OF SHOWERS ACROSS THE INTERIOR AND WESTERN PR
THIS AFTERNOON.
* COOLER TEMPERATURES AND BETTER RAIN CHANCES ARE ANTICIPATED
AROUND MID-WEEK NEXT WEEK DUE TO AN APPROACHING FRONTAL
BOUNDARY.
SHORT TERM(TODAY THROUGH SATURDAY)
ISSUED AT 500 AM AST THU DEC 18 2025
CALM WEATHER CONDITIONS PREVAILED ACROSS THE ISLANDS OVERNIGHT. THE
DOPPLER RADAR DETECTED SHOWERS MOVING ACROSS THE LOCAL WATERS,
WINDWARD AREAS OF PR AND THE USVI OVERNIGHT, WHILE THE LEEWARD AREAS
MAINLY REMAINED CLEAR. MINIMUM TEMPERATURES RANGED FROM THE LOW TO
MID-70S ALONG THE COAST TO THE LOW-60S IN THE MOUNTAINS AND VALLEYS.
WINDS WERE PRIMARILY FROM THE EAST WITH LAND BREEZE VARIATIONS.
A SUBSIDING NORTHERLY SWELL IS LIKELY (60 TO 80%) TO CONTINUE
PRODUCING HAZARDOUS BREAKING WAVES OF 9 TO 11 FEET AND A HIGH
LIKELIHOOD OF LIFE- THREATENING RIP CURRENTS ALONG EXPOSED NORTH-
FACING BEACHES OF PUERTO RICO AND CULEBRA THROUGH MUCH OF THE DAY.
BEACHES ALONG THE NORTH-FACING SHORES OF RINCON, AGUADA, ST.
JOHN, ST. THOMAS, AND ADJACENT ISLANDS HAVE A HIGH PROBABILITY
(60 TO 80%) OF EXPERIENCING DANGEROUS RIP CURRENT CONDITIONS.
WHILE THE SWELL IS EXPECTED TO GRADUALLY SUBSIDE, HAZARDOUS
COASTAL AND SURF CONDITIONS MAY PERSIST INTO THE AFTERNOON,
PARTICULARLY AT THE MOST EXPOSED BEACHES.
WINDS ARE VERY LIKELY (>80%) TO PREVAIL FROM THE EAST THIS MORNING,
SHIFTING TO EAST-NORTHEAST THIS EVENING AND INTO THE WEEKEND. AS
DRIER AIR MOVES INTO THE REGION AND A MID- TO UPPER-LEVEL RIDGE
BUILDS OVERHEAD, THERE IS A HIGH PROBABILITY (70 TO 80%) OF
LITTLE TO NO RAINFALL ACROSS MOST AREAS DURING THE MORNING AND
EARLY AFTERNOON. HOWEVER, AN APPROACHING PERTURBATION IS EXPECTED
TO INCREASE CLOUDINESS LATER TODAY, LEADING TO A LOW TO MODERATE
CHANCE OF SHOWERS (10 TO 40%) ACROSS WINDWARD AREAS OF PUERTO
RICO AND THE U.S. VIRGIN ISLANDS, AND A LOW TO MODERATE CHANCE (20
TO 50%) ACROSS INTERIOR AND WESTERN PUERTO RICO DURING THE
AFTERNOON AND EVENING HOURS.
FROM THIS EVENING INTO EARLY FRIDAY MORNING, INCREASING MOISTURE
WILL RESULT IN A MODERATE CHANCE OF RAINFALL (40 TO 60%) ACROSS
WINDWARD AREAS. UNDER THESE CONDITIONS, THERE IS A LIMITED RISK OF
LOCALIZED FLOODING ACROSS INTERIOR AND WESTERN PUERTO RICO THIS
AFTERNOON AND EVENING, FOLLOWED BY A LIMITED FLOODING RISK ACROSS
NORTH AND EAST WINDWARD AREAS OVERNIGHT INTO EARLY FRIDAY.
LOOKING AHEAD, MODEL GUIDANCE CONTINUES TO SHOW A HIGH LIKELIHOOD
(>70%) OF A STRENGTHENING RIDGE PATTERN OVER THE NORTHEAST
CARIBBEAN, PROMOTING SUBSIDENCE ALOFT AND A PERSISTENT TRADE-WIND
INVERSION. AS A RESULT, RESIDENTS AND VISITORS OF PR AND THE USVI
CAN EXPECT MOSTLY SUNNY TO PARTLY CLOUDY CONDITIONS MOST OF THE
TIME, WITH PERIODIC SURGES OF MOISTURE BRINGING PASSING SHOWERS,
PRIMARILY ACROSS WINDWARD AREAS AND REGIONAL WATERS AND, DUE TO
LOCAL SEA-BREEZE EFFECTS, ACROSS WESTERN PUERTO RICO DURING THE
AFTERNOONS. OVERALL, DAILY RAIN CHANCES ARE EXPECTED TO RANGE FROM
LOW (10 TO 20%) TO MODERATE (30 TO 50%).
LONG TERM(SUNDAY THROUGH THURSDAY)
ISSUED AT 500 AM AST THU DEC 18 2025
LATE IN THE WEEKEND AND INTO EARLY NEXT WEEK, A WEAK MID- TO
UPPER-LEVEL RIDGE WILL PREVAIL ACROSS THE REGION, SUPPORTING
GENERALLY STABLE ATMOSPHERIC CONDITIONS. DURING THIS PERIOD,
PRECIPITABLE WATER (PWAT) VALUES ARE EXPECTED TO REMAIN BELOW TO
NEAR SEASONAL CLIMATOLOGICAL LEVELS, RANGING FROM 1.2 TO 1.6
INCHES. AT THE SURFACE, PATCHES OF LOW-LEVEL MOISTURE WILL
CONTINUE TO MOVE THROUGH THE AREA, PRODUCING BRIEF PASSING SHOWERS
OVER WINDWARD SECTIONS OF THE ISLANDS. RAINFALL ACCUMULATIONS
SHOULD REMAIN LIMITED, ALTHOUGH ISOLATED AFTERNOON SHOWERS MAY
DEVELOP ACROSS WESTERN PUERTO RICO. FROM MIDWEEK ONWARD, THE MID-
LEVEL RIDGE WILL GRADUALLY WEAKEN AS A POLAR TROUGH DEPARTING THE
EASTERN UNITED STATES ADVANCES FROM THE NORTHWEST. THIS PATTERN
CHANGE WILL INCREASE ATMOSPHERIC INSTABILITY, WITH 500 MB
TEMPERATURES COOLING TO BELOW-NORMAL VALUES BETWEEN -7 AND -10
DEGREES CELSIUS. A TRANSITION TOWARD HIGHER RAIN CHANCES IS
ANTICIPATED, WITH MODERATE PROBABILITIES (50 TO 60%) FOR SCATTERED
TO NUMEROUS SHOWERS. AT THE SURFACE, AN ASSOCIATED FRONTAL
BOUNDARY IS FORECAST TO APPROACH THE REGION AROUND WEDNESDAY INTO
THURSDAY (CHRISTMAS EVE AND CHRISTMAS DAY) AND POTENTIALLY MOVE
ACROSS THE AREA. AS THE FRONT NEARS, MOISTURE WILL INCREASE, WITH
PWAT VALUES RISING TO BETWEEN 1.5 AND 1.8 INCHES, WITHIN THE
SEASONAL TO ABOVE-NORMAL RANGE. THE COMBINATION OF COOLER
TEMPERATURES ALOFT AND INCREASED MOISTURE SUPPORTS A MORE
UNSETTLED PATTERN DURING THE HOLIDAY PERIOD, INCLUDING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS. GUIDANCE, INCLUDING THE
GALVEZ-DAVISON INDEX, SUGGESTS THE POTENTIAL FOR SHALLOW
CONVECTION WITH ISOLATED THUNDERSTORM DEVELOPMENT. PERIODS OF
LOCALLY HEAVY RAINFALL MAY OCCUR, WHICH COULD ELEVATE THE RISK OF
LOCALIZED FLOODING IN FLOOD-PRONE AND POORLY DRAINED AREAS,
INCLUDING PONDING ON ROADWAYS. AT THIS TIME, THE EXTENDED FORECAST
INDICATES A LIMITED FLOOD RISK. ALSO, COOLER TEMPERATURES ARE
EXPECTED IN THE WAKE OF THE POSSIBLE FRONTAL PASSAGE.
AVIATION
(06Z TAFS)
ISSUED AT 500 AM AST THU DEC 18 2025
VFR CONDITIONS WILL PREVAIL THROUGH MUCH OF THE FORECAST PERIOD.
SHRA/-SHRA WILL THEN FORM OVER THE INTERIOR AND WESTERN PR (NEAR
JBQ) BTWN 18/17-23Z. THEN, A SURGE OF MOISTURE WILL INCREASE THE
CHANCE OF RAIN FROM 18/18Z ONWARD OVER JSJ/IST/ISX. WINDS WILL BE
CALM-LIGHT/VAR THRU THIS MORNING, THEN RETURN FROM THE E AFTER
18/13Z AT 10-15KT WITH HIGHER GUSTS AND SEA BREEZE VARIATIONS. WINDS
WILL TURN MORE FROM THE ENE FROM 18/18Z ONWARD.
MARINE
ISSUED AT 500 AM AST THU DEC 18 2025
MODERATE TO LOCALLY FRESH EAST-NORTHEAST WINDS WILL CONTINUE ACROSS
THE LOCAL WATERS TODAY. THESE WINDS, COMBINED WITH ADDITIONAL PULSES
OF A FADING NORTHERLY SWELL, WILL MAINTAIN HAZARDOUS MARINE CONDITIONS
FOR SMALL CRAFT, PARTICULARLY ACROSS THE ATLANTIC WATERS AND MONA
PASSAGE. AS A RESULT, SMALL CRAFT ADVISORIES REMAIN IN EFFECT THROUGH
AT LEAST LATE TONIGHT AND INTO MIDDAY FRIDAY. ANOTHER LONG-PERIOD
NORTHERLY SWELL IS ANTICIPATED TO ARRIVE AND SPREAD ACROSS THE LOCAL
ATLANTIC WATERS AND PASSAGES DURING THE WEEKEND, KEEPING HAZARDOUS
MARINE CONDITIONS INTO EARLY NEXT WEEK.
BEACH FORECAST
ISSUED AT 500 AM AST THU DEC 18 2025
A HIGH RISK OF RIP CURRENTS CONTINUES TODAY ALONG THE WESTERN,
NORTHERN, AND EASTERN BEACHES OF PUERTO RICO, AS WELL AS CULEBRA,
ST. THOMAS, AND ST. JOHN. THIS MEANS LIFE-THREATENING RIP CURRENTS
ARE LIKELY WITHIN THE SURF ZONE, AND BEACHGOERS SHOULD STRICTLY
FOLLOW THE GUIDANCE OF LIFEGUARDS, BEACH PATROL FLAGS, AND SIGNS.
TONIGHT, THE RISK WILL DECREASE TO MODERATE ALONG WESTERN PUERTO
RICO AND ST. THOMAS, WHILE REMAINING HIGH ALONG NORTHERN PUERTO
RICO AND CULEBRA THROUGH EARLY FRIDAY. MODERATE CONDITIONS ARE
EXPECTED FRIDAY INTO EARLY SATURDAY; HOWEVER, BEACH CONDITIONS ARE
FORECAST TO DETERIORATE AGAIN FROM SATURDAY AFTERNOON INTO SUNDAY
DUE TO STRENGTHENING WINDS AND ANOTHER NORTHERLY SWELL SPREADING
ACROSS THE LOCAL ATLANTIC WATERS. STAY TUNED TO THE FORECAST! 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-
008-012.
HIGH SURF ADVISORY UNTIL 6 PM AST THIS EVENING FOR PRZ001-002-
005-008.
HIGH RIP CURRENT RISK THROUGH THIS AFTERNOON FOR PRZ010.
HIGH SURF ADVISORY UNTIL 6 AM AST EARLY THIS MORNING FOR PRZ010.
HIGH RIP CURRENT RISK UNTIL 6 AM AST EARLY THIS MORNING FOR
PRZ011-013.
HIGH SURF ADVISORY UNTIL 6 PM AST THIS EVENING FOR PRZ012.
VI...HIGH RIP CURRENT RISK THROUGH THIS AFTERNOON FOR VIZ001.
AM...SMALL CRAFT ADVISORY UNTIL NOON AST FRIDAY FOR AMZ711.
SMALL CRAFT ADVISORY UNTIL MIDNIGHT AST TONIGHT FOR AMZ712-741.
SMALL CRAFT ADVISORY UNTIL 6 AM AST EARLY THIS MORNING FOR
AMZ716-723-726-742.
SHORT TERM...CAM
LONG TERM....YZR
AVIATION...CAM
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