617
FXCA62 TJSJ 310836
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
436 AM AST TUE DEC 31 2024
SYNOPSIS
A SURFACE HIGH-PRESSURE SYSTEM MIGRATING FROM THE WESTERN TO THE
CENTRAL ATLANTIC WILL ESTABLISH A TYPICAL WINTER ADVECTIVE WEATHER
PATTERN, BRINGING PLEASANT TROPICAL TEMPERATURES AND OCCASIONAL
DAILY SHOWERS TO PR AND USVI'S WINDWARD AREAS. NORTHEASTERLY SWELL
PULSES WILL GENERATE HAZARDOUS BREAKING WAVES, LEADING TO LIFE-
THREATENING RIP CURRENTS ALONG THE NORTH AND EAST-FACING BEACHES
OF THE U.S. VIRGIN ISLANDS AND PUERTO RICO THROUGH THIS EVENING.
BY NEXT WEEKEND, INSTABILITY AND RAINFALL ACTIVITY MAY INCREASE
SLIGHTLY TO MODERATELY DUE TO THE POTENTIAL APPROACH OF ANOTHER
COLD FRONT AND A POLAR TROUGH NEAR THE NORTHEAST CARIBBEAN.
ANOTHER LONG-PERIOD NORTHEASTERLY SWELL WILL DETERIORATE THE
MARINE AND COASTAL CONDITIONS BY THE WEEKEND AND EARLY NEXT WEEK.
SHORT TERM...TODAY THROUGH THURSDAY
ANOTHER CALM NIGHT PREVAILED WITH NE WINDS BRINGING POCKETS OF
MOISTURE ACROSS THE LOCAL ATLANTIC WATERS. TEMPERATURES REMAINED
LOWER THAN NORMAL, AS STATIONS IN THE URBAN AND COASTAL AREAS
REPORTED LOW 70S AND UPPER 60S WHILE THE INTERIOR SECTIONS OBSERVED
TEMPERATURES IN THE LOW 60S AND UPPER 50S.
THE COOLER AND ADVECTIVE PATTERN WILL CONTINUE THROUGH THE BEGINNING
OF THE NEW YEAR. THE HIGH SURFACE PRESSURE IN THE WESTERN ATLANTIC
AND THE LOW SURFACE PRESSURE IN THE CENTRAL ATLANTIC CONTINUE
INTERACTING AND PROMOTING THE NE WIND FLOW. TODAY, NEW YEAR'S EVE
WILL MOSTLY BE STABLE WITH FEW PASSING SHOWERS ALONG WINDWARD
SECTIONS. HOWEVER, A PATCH OF MOISTURE WILL MOVE ACROSS THE REGION
LATER TONIGHT, INCREASING MOISTURE CONTENT. THE LATEST MODEL
GUIDANCE SUGGESTS THAT PWAT VALUES WILL GRADUALLY INCREASE DURING
THE DAY, THE CHANCE OF PASSING SHOWERS MAINLY FOR NORTHWESTERN
PUERTO RICO, VIEQUES, CULEBRA, AND THE U.S. VIRGIN ISLANDS. EXPECT
PONDING OF WATER IN ROADWAYS AND POORLY DRAINED AREAS WITH SLIPPERY
STREETS, AND A LIMITED RISK OF FLOODING FOR THESE AREAS.
AS THE PATCH OF MOISTURE MOVES ACROSS THE REGION, A SHOWERY NEW
YEAR'S DAY IS ALSO ANTICIPATED ONCE AGAIN IN WINDWARD SECTIONS
EARLY IN THE MORNING AND SHALLOW CONVECTION ALONG SOUTHWESTERN
PORTIONS OF PUERTO RICO IN THE AFTERNOON. THE SURFACE HIGH
PRESSURE WILL MOVE SOUTHEASTWARD JUST NORTHEAST OF THE REGION,
BRINGING ANOTHER PATCH OF MOISTURE EARLY MORNING ON THURSDAY. THE
FRESHER TEMPERATURES WILL CONTINUE THROUGH THE REST OF THE
FORECAST PERIOD.
LONG TERM
FRIDAY THROUGH TUESDAY
A SURFACE HIGH PRESSURE BUILDING ACROSS THE CENTRAL ATLANTIC
NORTH OF THE ISLANDS WILL HOLD THE COLD FRONT TO THE NORTHWEST OF
THE ISLANDS ON FRIDAY. HOWEVER, AS THE COLD FRONT DRIFTS SLOWLY
EASTWARD NEAR THE NORTHEAST CARIBBEAN, AN INDUCED PRE-FRONTAL
TROUGH COULD DEVELOP OVER PR/USVI AROUND SATURDAY AFTERNOON INTO
SUNDAY. THE TRADE WINDS WILL ALSO CONTINUE TO ADVECT A COOLER AIR
MASS, THUS EXTENDING THE PERIOD OF PLEASANT TROPICAL WINTER
TEMPERATURES. MEANWHILE, POCKETS OF MOISTURE EMBEDDED IN THE
TRADES WILL OCCASIONALLY BRING QUICK PASSING SHOWERS. ALONG WITH
THE FRONT, A MID-TO UPPER-LEVEL TROUGH WILL PASS NEAR THE ISLANDS,
INCREASING LOCAL INSTABILITY OVER THE WEEKEND AND NEXT WEEK.
GIVEN THIS WEATHER PATTERN, WE CAN ANTICIPATE AN INCREASE IN
SHOWER ACTIVITY, ALONG WITH A SLIGHT TO MODERATE CHANCE OF
ISOLATED TO SCATTERED THUNDERSTORMS.
GFS HAS THE FRONTAL BOUNDARY LINGERING NORTH OR NEAR THE ISLANDS
AS IT INTERACTS WITH ONE HIGH PRESSURE OVER THE CENTRAL ATLANTIC
AND ANOTHER SURFACE HIGH BEHIND THE FRONT. MEANWHILE, THE ECMWF
MODEL SUGGESTS FROPA AROUND LATE SUNDAY NIGHT OR EARLY MONDAY
MORNING. THESE TWO SCENARIOS COULD RESULT IN SHOWERY OR DRIER,
WINDY, AND COOLER WEATHER EARLY NEXT WEEK, GFS AND ECMWF,
RESPECTIVELY. THEREFORE, WE WILL EXAMINE THIS POSSIBILITY MORE
CLOSELY AS THE DAYS APPROACHES.
AVIATION
(06Z TAFS)
EXPECT CALM TO LIGHT AND VRB WINDS THRU 31/12Z, THEN, OUT FROM THE
NE AT 8 TO 12 KT WITH HIGHER GUSTS AND SEA BREEZE VARIATIONS.
ALSO, MOSTLY VFR CONDS ARE EXPECTED THROUGH THE FCST PRD. VCSH ARE
EXPECTED BTW 31/18-01/22Z AND MAY REDUCE CIG/VIS FOR TJSJ, TIST,
AND TISX. PATCHES OF CLOUDS WILL RESULT IN BKN TO OVC AT
FL020-FL060 AT TIME. POSSIBLE FU AND MVFR CONDS AT TJSJ DUE TO
FIREWORKS BTW 01/03 - 01/06Z.
MARINE
MODERATE NORTHEAST WINDS IN PLACE FOR EARLY THIS WEEK UNDER A SURFACE
HIGH PRESSURE IN THE WESTERN ATLANTIC AND SURFACE LOW OVER THE
CENTRAL ATLANTIC. SEAS UP TO AND EXCEEDING 7 FEET WILL CONTINUE WITH
THE NORTHERLY SWELL THROUGH AT LEAST THIS AFTERNOON. ANOTHER FRONT
FROM THE EASTERN US WILL MOVE INTO THE WESTERN ATLANTIC BY MIDWEEK,
APPROACHING THE NORTHEAST CARIBBEAN BY THE WEEKEND. ANOTHER LONG-
PERIOD NORTHERLY SWELL WILL PROMOTE HAZARDOUS SEAS BY THE END OF THIS
WEEK THROUGH THE WEEKEND.
BEACH FORECAST
NORTHEASTERLY SWELL PULSES ARE SLOWLY FADING ACROSS THE ATLANTIC
OFFSHORE WATERS AND CARIBBEAN PASSAGES, GENERATING DANGEROUS
BREAKING WAVES ALONG THE NORTH- AND EAST-FACING BEACHES OF PUERTO
RICO AND THE U.S. VIRGIN ISLANDS. A HIGH SURF ADVISORY IS IN
EFFECT UNTIL 6 PM AST THIS EVENING FOR NORTH-FACING BEACHES IN
PUERTO RICO, FROM AGUADILLA TO FAJARDO, INCLUDING CULEBRA.
ADDITIONALLY, A HIGH RISK OF RIP CURRENTS IS IN EFFECT FOR THESE
BEACHES THROUGH AT LEAST 6 AM AST WEDNESDAY, AS WELL AS FOR THE
BEACHES OF RINCóN, AGUADA, AND THE U.S. VIRGIN ISLANDS. MEANWHILE,
THE SOUTHERN PROTECTED BEACHES OF PUERTO RICO REMAIN UNDER A LOW
RISK OF RIP CURRENTS.
COASTAL CONDITIONS WILL DETERIORATE AGAIN AROUND FRIDAY THROUGH
THE WEEKEND WITH THE ARRIVAL OF ANOTHER LONG-PERIOD NORTHERLY
SWELL. FOR MORE DETAILS, REFER TO THE COASTAL HAZARD MESSAGE
(CFWSJU) AND SURF ZONE FORECAST (SRFSJU).
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-
005-008-012.
HIGH RIP CURRENT RISK THROUGH THIS AFTERNOON FOR PRZ010.
VI...HIGH RIP CURRENT RISK THROUGH THIS AFTERNOON FOR VIZ001-002.
AM...SMALL CRAFT ADVISORY UNTIL NOON AST TODAY FOR AMZ711-712-716-723-
741-742.
SYNOPSIS/LONG TERM/MARINE/BEACH FORECAST...CAM
SHORT TERM/AVIATION...MNG
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