870
FXCA62 TJSJ 160909
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
509 AM AST SAT NOV 16 2024
SYNOPSIS
A FRONTAL BOUNDARY NORTH OF THE AREA, FOLLOWED BY ANOTHER
APPROACHING COLD FRONT TONIGHT, WILL MAINTAIN WET AND UNSTABLE
CONDITIONS AND WILL CONTINUE TO PROMOTE SHOWERS AND THUNDERSTORMS
ACROSS THE LOCAL ISLANDS DURING THE WEEKEND. AFTER THE APPROACHING
COLD FRONT CROSSES THE REGION TOMORROW, A DRIER AND COOLER AIR
MASS WILL BE REACH THE AREA BY MONDAY AND LINGER THROUGH MIDWEEK.
A NORTHERLY SWELL WILL CONTINUE TO REACH THE REGIONAL WATERS,
DETERIORATING MARINE AND COASTAL CONDITIONS THROUGH MONDAY. SMALL
CRAFT ADVISORIES, HIGH SURF ADVISORIES AND HIGH RISK OF RIP
CURRENTS ARE IN EFFECT.
SHORT TERM...TODAY THROUGH MONDAY
STRONG THUNDERSTORMS WERE OBSERVED ACROSS THE WESTERN OFFSHORE
ATLANTIC AND OVER THE CARIBBEAN WATERS. THESE STORMS MOVED ACROSS
SOUTHWEST AND SOUTHEAST PUERTO RICO, BUT THE HEAVIEST ACCUMULATIONS
STAYED OVER THE WATERS. FOR SAINT THOMAS AND SAINT JOHN, THE STORMS
MANAGED TO MOVE INLAND, WITH HEAVY DOWNPOURS, LIGHTING AND
ACCUMULATIONS AROUND ONE INCH.
A STATIONARY FRONT IS CAUSING THESE SHOWERS, AND ITS REMNANTS
WILL MAINTAIN HIGH MOISTURE LEVELS ACROSS THE REGION. THERE IS
ALSO A TROUGH AT ALL LEVELS, WITH ITS AXIS WEST OF THE REGION.
THIS HAS CAUSED THE WINDS TO SHIFT FROM THE SOUTHWEST TODAY,
ALTHOUGH LIGHT. WITH WINDS COMING FROM THIS DIRECTION, THE MORNING
SHOWERS ARE EXPECTED FOR WESTERN AND SOUTHWESTERN PUERTO RICO,
AND FOR THE VICINITY OF THE VIRGIN ISLANDS. IN THE AFTERNOON, WITH
ENOUGH INSTABILITY AND LOCAL EFFECTS, THE HEAVY RAIN IS
ANTICIPATED FOR THE SAN JUAN METRO AREA AND NORTHEASTERN PUERTO
RICO. URBAN AND SMALL FLOODING AND WATER SURGES ALONG RIVERS CAN
BE EXPECTED WITH THIS ACTIVITY.
ANOTHER FRONTAL BOUNDARY IS EXPECTED TO MAKE ITS WAY INTO THE REGION
LATER TONIGHT AND TOMORROW, WITH MORE SHOWERS AND THUNDERSTORMS IN
THE FORECAST. THE WINDS WILL REMAIN MOSTLY LIGHT AND FROM THE WEST,
SO WHILE THE RAIN WILL BE MOVING FROM THE MONA CHANNEL AND THE
CARIBBEAN INTO PUERTO RICO, THE AFTERNOON ACTIVITY SHOULD DEVELOP IN
THE EASTERN HALF OF PUERTO RICO, PROGRESSING TOWARD VIEQUES,
CULEBRA AND THE VIRGIN ISLANDS. ONCE AGAIN, THE RISK FOR URBAN AND
SMALL STREAM FLOODING WILL BE ELEVATED.
CHANGES IN THE PATTERN ARE IN STORE FOR THE START OF THE WORKWEEK.
AS THE FRONTAL BOUNDARY CROSSES THE REGION, THE AIR MASS WILL DRY
OUT AND WINDS WILL SHIFT FROM THE NORTH. CONDITIONS WILL BECOME
UNFAVORABLE FOR STRONG SHOWERS TO DEVELOP AND GENERALLY FAIR WEATHER
WILL PERSIST. ADDITIONALLY, 925 MB TEMPERATURES WILL DROP BELOW
NORMAL, SO COOLER TEMPERATURES ARE IN THE FORECAST.
LONG TERM...TUESDAY THROUGH FRIDAY
A DECREASE IN PRECIPITABLE WATER VALUES (PWAT) IS FORECAST TO
CONTINUE BY THE START OF THE LONG TERM FORECAST PERIOD. CURRENT
MODEL GUIDANCE HAS PWAT VALUES OF 0.9 TO 1.2 INCHES, WELL BELOW TO
BELOW NORMAL VALUES FOR THIS TIME OF THE YEAR. THIS IS DUE TO A
COOLER AND DRIER AIR MASS FILTERING INTO THE REGION UNDER NORTHERLY
FLOW BEHIND THE FRONTAL BOUNDARY MENTIONED AT THE END OF THE SHORT
TERM PERIOD. 850MB TO 700MB RELATIVE HUMIDITY AND 925MB TEMPERATURES
ARE FORECAST TO BE BELOW NORMAL TO START THE LONG TERM PERIOD. A MID
TO UPPER LEVEL RIDGE WILL MOVE IN FROM THE SOUTHEASTERN UNITED
STATES INTO THE WESTERN CARIBBEAN, MAINTAINING A TRADE WIND CAP
INVERSION AROUND 850 MB, WITH ALL THE LOW LEVEL MOISTURE TRAPPED
BELOW THIS LEVEL. THROUGH WEDNESDAY, GENERALLY LOW PROBABILITY OF
PRECIPITATION (POP) WILL REMAIN, EXCEPT JUST SOUTHEAST OF SAINT
CROIX, WHERE REMNANT MOISTURE OF THE COLD FRONT WILL LINGER.
PWAT VALUES WILL CLIMB BACK UP ONCE WINDS VEER TO BECOME MORE
EASTERLY ON THURSDAY AND GAIN A SOUTHERLY COMPONENT ON FRIDAY. THIS
CHANGE IN WIND DIRECTION WILL BE DUE TO A SURFACE HIGH MOVING FROM
THE EAST TO CENTRAL ATLANTIC. MOISTURE WILL BE BROUGHT IN FROM THE
EAST AND SOUTH, INCREASING THE POTENTIAL FOR SHOWERS AND AFTERNOON
CONVECTION. TEMPERATURES WILL ONCE AGAIN REACH THE UPPER 80S TO LOW
90S ACROSS LOWER ELEVATIONS OF THE ISLANDS.
AVIATION
(06Z TAFS)
SHRA AND TSRA WILL PERSIST ACROSS THE CARIBBEAN WATERS, REACHING
TJPS AND THE USVI TERMINALS AT TIMES. AFTER 17Z,ADDITIONAL
ACTIVITY IS ALSO EXPECTED NEAR TJSJ. PERIODS OF REDUCED VIS AND
LOW CEILINGS ARE ANTICIPATED. THE WINDS ARE FROM THE SW THROUGH
13-15Z, THEN SHIFTING FROM THE WEST THROUGH THE FORECAST PERIOD.
SPEEDS ARE AT 4-10 KTS, WITH STRONGER GUSTS NEAR THUNDERSTORMS.
MARINE
GENTLE TO MODERATE WESTERLY WINDS WILL PREVAIL TODAY AND TONIGHT,
BECOMING NORTHERLY TOMORROW AND NORTHEASTERLY ON MONDAY. MARINE
CONDITIONS WILL BE UNFAVORABLE FOR SMALL CRAFT THROUGH MONDAY
DUE TO PULSES OF NORTHERLY SWELLS. A FRONTAL BOUNDARY NORTH OF THE
REGION AND ASSOCIATED MOISTURE, WILL INCREASE THE CHANCE FOR SHOWERS
AND ISOLATED THUNDERSTORMS ACROSS THE REGIONAL WATERS AND
PASSAGES. SMALL CRAFT ADVISORIES ARE IN EFFECT TODAY FOR THE
COASTAL AND OFFSHORE ATLANTIC WATERS AND LOCAL PASSAGES. AFTER 6
PM AST AND THROUGH NOON AST ON MONDAY, SMALL CRAFT ADVISORIES FOR
THE COASTAL AND OFFSHORE ATLANTIC WATERS WILL REMAIN.
BEACH FORECAST
PULSES OF NORTHERLY SWELL WILL MAINTAIN DETERIORATED COASTAL
CONDITIONS, MAINLY ACROSS ATLANTIC FACING COASTLINES, AND THEY
CONTINUE TO BE DETECTED BY BUOY 41043 (AROUND 174 NM N-NNE OF SAN
JUAN) AND BUOY 41044 (AROUND 460 NM ENE OF SAN JUAN). A HIGH SURF
ADVISORY WILL BE IN EFFECT THROUGH 6 AM AST SUNDAY FOR THE
NORTHERN COASTLINE OF PUERTO RICO FROM AGUADILLA TO FAJARDO, AS
WELL AS FOR CULEBRA, ST. THOMAS AND ST. JOHN. A HIGH SURF ADVISORY
IS ALSO IN EFFECT FOR THE BEACHES OF AGUADA AND RINCON THROUGH 6
PM AST THIS EVENING. A HIGH RISK OF RIP CURRENTS IS IN EFFECT FOR
THE NORTHERN COASTLINE OF PUERTO RICO FROM RINCON TO FAJARDO,
INCLUDING CULEBRA, AS WELL AS FOR ST. THOMAS AND ST. JOHN THROUGH
6 PM AST MONDAY. A HIGH RISK OF RIP CURRENTS IS ALSO IN EFFECT FOR
VIEQUES THROUGH 6 PM AST THIS EVENING. FOR MORE INFORMATION,
PLEASE REFER TO THE SRFSJU AND CFWSJU.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HIGH RIP CURRENT RISK THROUGH MONDAY AFTERNOON FOR PRZ001-002-
005-008-010-012.
HIGH SURF ADVISORY UNTIL 6 AM AST SUNDAY FOR PRZ001-002-005-008-
012.
HIGH SURF ADVISORY UNTIL 6 PM AST THIS EVENING FOR PRZ010.
HIGH RIP CURRENT RISK THROUGH THIS AFTERNOON FOR PRZ013.
VI...HIGH RIP CURRENT RISK THROUGH MONDAY AFTERNOON FOR VIZ001.
HIGH SURF ADVISORY UNTIL 6 AM AST SUNDAY FOR VIZ001.
AM...SMALL CRAFT ADVISORY UNTIL NOON AST MONDAY FOR AMZ711-712-716.
SMALL CRAFT ADVISORY UNTIL 6 PM AST THIS EVENING FOR AMZ723-741-
742.
SHORT TERM...ERG
LONG TERM....MRR
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