931
FXCA62 TJSJ 040823
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
423 AM AST SAT JAN 4 2025
KEY MESSAGES
* UNSETTLED AND WET CONDITIONS (INCREASED SHOWER ACTIVITY) WILL
CONTINUE THROUGH SUNDAY, WITH ISOLATED THUNDERSTORMS POSSIBLE,
POTENTIALLY LEADING TO LOCALIZED FLOODING IMPACTS.
* NORTHERLY SWELLS AND STRENGTHENING NORTHEASTERLY WINDS WILL CREATE
CHOPPY TO HAZARDOUS SEAS FOR SMALL CRAFT OVER THE HOLIDAY WEEKEND.
* LIFE-THREATENING RIP CURRENTS WILL CONTINUE THROUGH AT LEAST
EARLY NEXT WEEK ACROSS THE NORTHERN AND EASTERN EXPOSED
BEACHES.
SHORT TERM...TODAY THROUGH MONDAY
OVERNIGHT, RELATIVELY CALM WEATHER CONDITIONS PREVAILED ACROSS THE
ISLANDS, PARTICULARLY OVER THE WESTERN HALF OF PUERTO RICO. IN
CONTRAST, THE EASTERN HALF, AS WELL AS VIEQUES AND CULEBRA,
EXPERIENCED PASSING SHOWERS THROUGHOUT THE NIGHT, WITH RAINFALL
ACCUMULATIONS AROUND A QUARTER OF AN INCH TO HALF AN INCH OVER
NORTHEASTERN PUERTO RICO AND PORTIONS OF THE SAN JUAN METROPOLITAN
AREA. SURFACE WEATHER OBSERVATIONS INDICATED TEMPERATURES IN THE
70S IN COASTAL AND URBAN AREAS, WHILE MOUNTAINOUS AND RURAL AREAS
EXPERIENCED TEMPERATURES IN THE 60S. NORTHEASTERLY WINDS WERE
PRESENT AT SPEEDS OF AROUND 5 TO 10 MPH.
THE LATEST MODEL GUIDANCE CONTINUES TO SUGGEST A BUILDING SURFACE
HIGH-PRESSURE OVER THE SOUTHWESTERN ATLANTIC. THIS WEATHER FEATURE
IS EXPECTED TO PUSH A FRONTAL BOUNDARY TOWARD THE REGION. AS IT
APPROACHES FROM THE WEST, IT WILL INDUCE A PRE-FRONTAL TROUGH,
INCREASING MOISTURE LEVELS AND PRECIPITABLE WATER (PW) CONTENT TO
APPROXIMATELY TWO STANDARD DEVIATIONS DURING THE WEEKEND. PW IS
FORESEEN TO PEAK ON SUNDAY, REACHING UP TO 2 INCHES. AS NOTED IN
PREVIOUS DISCUSSIONS, INSTABILITY WILL GRADUALLY INCREASE TODAY,
PEAKING ON SUNDAY, AS INDICATED BY COOLER 500 MB TEMPERATURES AND
RISING GALVEZ-DAVIDSON INDEX VALUES. THIS SHIFT IN THE WEATHER
PATTERN WILL LEAD TO SCATTERED TO NUMEROUS SHOWERS IN THE MORNINGS,
ESPECIALLY ACROSS NORTHERN AND NORTHEASTERN PUERTO RICO, VIEQUES,
CULEBRA, AND THE U.S. VIRGIN ISLANDS, ALONG WITH A SLIGHT TO
MODERATE CHANCE OF ISOLATED THUNDERSTORMS. ADDITIONAL ACTIVITY IS
ALSO EXPECTED IN THE WEST-CENTRAL AND SOUTHWESTERN SECTIONS OF
PUERTO RICO AS THE DAY PROGRESSES. CONSEQUENTLY, THERE WILL BE A
LIMITED TO LOCALIZED ELEVATED RISK OF FLOODING DUE TO THE POTENTIAL
FOR PONDING WATER ON ROADWAYS, POORLY DRAINED AREAS, AND URBAN AND
SMALL STREAM FLOODING.
WEATHER CONDITIONS ARE EXPECTED TO GRADUALLY IMPROVE FROM SUNDAY
NIGHT ONWARD AS SEASONAL PWAT VALUES RETURN WITH THE ARRIVAL OF A
SLIGHTLY DRIER AIR MASS AND THE ESTABLISHMENT OF A RIDGE ALOFT. IT
IS WORTH NOTING THAT AS THE THREE KINGS DAY APPROACHES, IT IS
UNLIKELY THAT SIGNIFICANT DISRUPTIVE WEATHER EVENTS WILL OCCUR
DURING THE CELEBRATIONS. ON THE MORNING OF JANUARY 6TH, BOTH
RESIDENTS AND VISITORS IN PUERTO RICO AND THE U.S. VIRGIN ISLANDS
CAN EXPECT BRIEF SHOWERS, PRIMARILY DRIVEN BY RESIDUAL MOISTURE FROM
A RECENT COLD FRONT AND THE ASSOCIATED PRE-FRONTAL TROUGH THAT
AFFECTED THE REGION.
LONG TERM...TUESDAY THROUGH SATURDAY
OVERALL, FAIR WEATHER CONDITIONS WILL PREVAIL OVER THE LONG-TERM
PERIOD. THE PRECIPITABLE WATER CONTENT WILL FLUCTUATE BETWEEN NORMAL
AND BELOW-NORMAL LEVELS (1.0-1.5 INCHES), WITH UPPER-LEVEL HIGHS
BUILDING OVER THE SOUTHEASTERN CARIBBEAN. TWO WEAK COLD FRONTS ARE
FORECAST TO REACH THE LOCAL AREA AT THE END OF THE WORKWEEK AND LATE
SUNDAY, WITH ASSOCIATED UPPER-LEVEL TROUGHS PASSING MAINLY NORTH OF
THE AREA, PROVIDING ONLY SLIGHT INSTABILITY OVER THE ISLANDS.
HOWEVER, BY MIDWEEK, AS THE SURFACE HIGH OVER THE CENTRAL ATLANTIC
MOVES FURTHER EAST AND THE PRESSURE GRADIENT RELAXES OVER THE
EASTERN CARIBBEAN, A PRE-FRONTAL TROUGH SHOULD DEVELOP MAINLY EAST
OF THE LEEWARD ISLANDS, CAUSING WINDS BRIEFLY TO ACQUIRE AN EAST TO
SOUTHEASTERLY DIRECTION AND BECOME LIGHT TO CALM EARLY IN THE
PERIOD. MOISTURE ADVECTION SHOULD FAVOR SHOWERS OVER THE USVI, BUT
MINOR RAINFALL AMOUNTS ARE EXPECTED WITH THIS ACTIVITY. MODERATE TO
FRESH NE TO NNE WINDS WILL RETURN BY THURSDAY AND FRIDAY AS THE
FRONT APPROACHES THE LOCAL AREA.
A SIMILAR WEATHER PATTERN IS EXPECTED DURING THE WEEKEND, AS THE
PRESSURE GRADIENT RELAXES AGAIN ON SATURDAY BEFORE THE ARRIVAL OF
THE NEXT FRONT ON SUNDAY. PLEASANT TEMPERATURES WILL CONTINUE DURING
THE FORECAST PERIOD, ESPECIALLY DURING CLEAR NIGHTS WITH CALM WINDS
AND AFTER THE FRONTAL PASSAGES.
AVIATION
(06Z TAFS)
A FRONTAL BOUNDARY OVER THE ATLANTIC WTRS WILL CONTINUE SINK
SOUTHWARDS ACROSS THE LOCAL AREA. INCREASING SHRA EXPECTED ACROSS
TJSJ, TJBQ, AND THE USVI TERMINALS THRU THE REST OF THE MORNING
HOURS, WITH SHRA AFFECTING TJPS AFTER 04/16Z. THIS COULD RESULT IN
BRIEF MVFR CONDITIONS WITH SCT-BKN CEILINGS BTW FL025-050. WINDS
WILL REMAIN FROM THE EAST-NORTHEAST AT 6-12 KT, WITH HIGHER GUSTS
AND SEA BREEZE INFLUENCES, BECOMING MORE NNE-N AND INCREASING AFT
04/21Z. SHRA AND POSSIBLE -TSRA EXPECTED ACROSS THE ATLANTIC
WATERS AND NORTHERN TERMINALS OF THE ISLANDS DURING THE
EVENING/NIGHTTIME.
MARINE
MODERATE EAST TO NORTHEASTERLY WINDS WILL PREVAIL THROUGH THIS
MORNING AS THE SURFACE HIGH WEAKENS OVER THE CENTRAL ATLANTIC AND A
COLD FRONT WITH ASSOCIATED SHEARLINE APPROACHES THE AREA FROM THE
NORTHWEST LATER THIS WEEKEND. THIS WILL PROMOTE MODERATE TO FRESH
NORTHEASTERLY WINDS THROUGH AT LEAST MONDAY. A LONG-PERIOD NORTHEAST
SWELL WILL CONTINUE TO SPREAD ACROSS THE ATLANTIC WATERS AND
PASSAGES THROUGH THE REST OF THE WEEKEND. A LARGER NORTHWEST SWELL
WILL ARRIVE ON SUNDAY AND LINGER THROUGH EARLY NEXT WEEK. THE
COMBINATION OF THE SWELLS WITH INCREASING WINDS WILL PROMOTE SMALL
CRAFT ADVISORY CONDITIONS DUE TO HAZARDOUS SEAS ACROSS THE LOCAL
WATERS THROUGH AT LEAST TUESDAY.
PLEASE REFER TO THE LATEST COASTAL WATERS FORECAST (CWFSJU) AND
MARINE WEATHER MESSAGE (MWWSJU) FOR ADDITIONAL INFORMATION.
BEACH FORECAST
A LONG-PERIOD NORTHEASTERLY SWELL WILL CONTINUE TO SPREAD ACROSS THE
LOCAL WATERS THROUGH THE WEEKEND. THIS SWELL WILL INCREASE THE RISK
OF LIFE-THREATENING RIP CURRENTS WITH ROUGH SURF CONDITIONS ALONG
THE NORTHERN EXPOSED BEACHES OF THE ISLANDS. IN ADDITION, A LARGER
LONG-PERIOD NORTHWESTERLY SWELL WILL ARRIVE ON SUNDAY AND LINGER
THROUGH EARLY NEXT WEEK, CAUSING LARGE BREAKING WAVES THAT WILL LEAD
TO HIGH SURF ADVISORY CONDITIONS, MINOR BEACH EROSION, AND LIFE-
THREATENING RIP CURRENTS, PARTICULARLY ALONG THE ATLANTIC COASTLINE
OF PUERTO RICO FROM RINCON TO FAJARDO, AND CULEBRA. ACROSS THE U.S.
VIRGIN ISLANDS, LIFE-THREATENING RIP CURRENTS WILL PREVAIL ACROSS
ALL NORTHERN EXPOSED BEACHES DUE TO THE LONG PERIOD SWELLS.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HIGH RIP CURRENT RISK THROUGH LATE MONDAY NIGHT FOR PRZ001-002-
005-008-010-012.
VI...HIGH RIP CURRENT RISK THROUGH LATE MONDAY NIGHT FOR VIZ001-002.
AM...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO NOON AST TUESDAY
FOR AMZ711.
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM AST TUESDAY
FOR AMZ712-741-742.
SMALL CRAFT ADVISORY FROM 6 AM SUNDAY TO NOON AST TUESDAY FOR
AMZ716-723.
SHORT TERM...MMC/ICP
LONG TERM...DSR/ICP
AVIATION...MMC/ICP
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