481
FXCA62 TJSJ 040859
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
459 AM AST TUE MAR 4 2025
SYNOPSIS
UNSTABLE WEATHER CONDITIONS WILL PERSIST TODAY THROUGH THE END OF
THE WORKWEEK AS A TROUGH CROSSES THE FORECAST AREA. EXPECT SHOWER
AND ISOLATED THUNDERSTORM ACTIVITY DURING THIS PERIOD. MORE STABLE
WEATHER CONDTIONS EXPECTED THIS WEEKEND. A NORTHWESTERLY SWELL
WILL REACH THE ATLANTIC WATERS THIS WEEKEND RESULTING IN POTENTIAL
HAZARDOUS SEAS AND BEACH CONDITIONS.
SHORT TERM...TODAY THROUGH THURSDAY
THE AXIS OF A SURFACE TROUGH WAS LOCATED JUST EAST OF THE VIRGIN
ISLANDS EARLY THIS MORNING. THIS TROUGH MAINTAINS THE WINDS FROM THE
NORTHEAST, BRINGING A FEW SHOWERS ACROSS THE VIRGIN ISLANDS, AND THE
NORTH AND EAST COAST OF PUERTO RICO. OTHER THAN THAT, LOTS OF CLOUDS
LINGERED ACROSS SOUTHWESTERN PUERTO RICO, WHILE VARIABLY CLOUDY
SKIES WERE OBSERVED ELSEWHERE.
A MID TO UPPER LEVEL TROUGH IS LOCATED JUST TO THE NORTHWEST OF THE
AREA. INSTABILITY ALOFT IS EXPECTED TO INCREASE, WITH MID-LEVEL
TEMPERATURES COOLING DOWN TODAY AND TOMORROW. THIS SYSTEM MAINTAINS
THE TRADE WINDS WEAK, GENERALLY COMING OUT OF THE SOUTHEAST AT 7 TO
9 KTS. THE SURFACE TROUGH WILL INCREASE MOISTURE, FROM THE SURFACE
TO NEARLY 700 MB. IN FACT, PRECIPITABLE WATER VALUES ARE EXPECTED TO
BE ABOVE NORMAL THROUGH WEDNESDAY, AROUND 1.6-1.8 INCHES. THIS WILL
TRANSLATE INTO ANOTHER ACTIVE AFTERNOON, WITH WIDESPREAD SHOWERS,
AND EVEN THUNDERSTORMS DEVELOPING. FOR EASTERN PUERTO RICO AND THE
VIRGIN ISLANDS, THE FREQUENCY OF SHOWERS WILL INCREASE THIS MORNING
AND EARLY IN THE AFTERNOON HOURS. HOWEVER, THE STRONGEST ACTIVITY IS
ANTICIPATED AGAIN FOR THE INTERIOR AND WESTERN PUERTO RICO. SINCE
THE AXIS OF THE TROUGH WILL BE LIKELY CROSSING THE AREA EARLY THIS
AFTERNOON, IT IS NOT CLEAR WHETHER THE WINDS WILL SHIFT ON TIME TO
MOVE THE SHOWERS INTO THE NORTHWESTERN CORNER OF PUERTO RICO OR IF
THE MAIN FOCUS WILL BE THE SOUTHWEST, LIKE YESTERDAY. DUE TO THIS
UNCERTAINTY, AN ELEVATED FLOODING RISK IS SHOWN FOR ALL THE WESTERN
MUNICIPALITIES OF PUERTO RICO, AS THESE RAINS COULD RESULT IN URBAN
AND SMALL STREAM FLOODING, WATER SURGES, AND ISOLATED MUDSLIDES.
A SIMILAR STORY IS EXPECTED FOR TOMORROW, BUT BY THURSDAY, THE MID
TO UPPER LEVEL TROUGH WILL DEPARTS AND A RIDGE WILL BUILD BEHIND.
CONDITIONS ALOFT WILL NO LONGER FAVOR THE FORMATION OF
THUNDERSTORMS, BUT ENOUGH SURFACE MOISTURE WILL DRAG ADDITIONAL
SHOWERS ACROSS EASTERN PUERTO RICO AND THE VIRGIN ISLANDS, WHILE
ANOTHER ROUND OF SHOWERS IS ANTICIPATED FOR THE WEST IN THE
AFTERNOON HOURS.
TEMPERATURES WILL CONTINUE TO COOL DOWN IN THE OVERNIGHT HOURS, WITH
VALUES IN THE LOW AND MID 60S FOR THE MOUNTAIN, AND THE MID 70S FOR
COASTAL AREAS. HOWEVER, IT WILL WARM UP DURING THE DAYTIME. RIGHT
NOW, 925 MB TEMPERATURES ARE EXPECTED TO BE ONE TO TWO STANDARD
DEVIATION ABOVE THE CLIMATOLOGICAL VALUE, MEANING THAT HIGHS WILL
REACH THE MID TO UPPER 80S IN AREAS WITHOUT ANY SIGNIFICANT
AFTERNOON RAIN.
LONG TERM...FRIDAY THROUGH TUESDAY
FRIDAY WILL BE A TRANSITION DAY AS MARGINAL INSTABILITY FROM
LINGERING TROUGHINESS ALOFT, COMBINED WITH SUFFICIENT LOW-LEVEL
MOISTURE, PERSISTS. AT THE SURFACE, A FRONTAL BOUNDARY WILL CONTINUE
APPROACHING FROM THE NORTHWEST. AHEAD OF IT, A SHEARLINE WITH AN
ASSOCIATED COL REGION WILL MOVE ACROSS THE FORECAST AREA, CAUSING
WIND SPEEDS TO PLUMMET.
DURING THE MORNING HOURS, EXPECT SCATTERED SHOWERS TO DEVELOP OVER
REGIONAL WATERS, OCCASIONALLY DRIFTING INLAND ACROSS EASTERN PUERTO
RICO AND THE SMALLER ISLANDS. BY THE AFTERNOON, DIURNAL HEATING,
COMBINED WITH LINGERING MOISTURE AND INSTABILITY, WILL PROMOTE
CONVECTIVE DEVELOPMENT. WEAK STEERING WINDS WILL ENHANCE SEA BREEZE
CONVERGENCE AND OROGRAPHICALLY DRIVEN CONVECTION, POTENTIALLY
RESULTING IN ISOLATED THUNDERSTORMS. ADDITIONALLY, SLOW-MOVING
SHOWERS WILL ELEVATE THE RISK OF LOCALIZED FLOODING, PARTICULARLY
ALONG THE CENTRAL MOUNTAIN RANGE OF PUERTO RICO, WHERE LIMITED TO
MODERATE FLOODING IS POSSIBLE.
FOR THE REMAINDER OF THE LONG-TERM PERIOD, MOISTURE LEVELS WILL
REMAIN NEAR TO BELOW NORMAL, WHILE UPPER-LEVEL DYNAMICS WILL REMAIN
MOSTLY STABLE. THIS STABILITY IS SUPPORTED BY INCREASING 250 MB
HEIGHT FIELDS AND SLIGHTLY WARMER-THAN-USUAL 500 MB TEMPERATURES AS
A MID-LEVEL RIDGE BUILDS OVER THE NORTHEASTERN CARIBBEAN. SHOWER
ACTIVITY WILL FOLLOW A SEASONAL WEATHER PATTERN, WITH PASSING
SHOWERS MOVING OVER WINDWARD COASTAL AREAS DURING THE NIGHT AND
MORNING HOURS. BY THE AFTERNOON, LOCALIZED SHALLOW CONVECTION WILL
DEVELOP ACROSS WESTERN PUERTO RICO. HOWEVER, GIVEN THE STABLE
CONDITIONS AND LIMITED MOISTURE, NO SIGNIFICANT FLOODING RISK IS
ANTICIPATED.
AVIATION
(06Z TAFS)
ISOLATED TO SCATTERED SHRA EXPECTED THIS MORNING FOR THE LOCAL
WATERS, OCCASIONALLY MOVING OVER THE VIRGIN ISLANDS AND TJSJ
TERMINALS. AFTER 17Z, SHRA AND TSRA ARE EXPECTED FOR THE CORDILLERA
CENTRAL, POTENTIALLY REACHING TJSJ, TJBQ AND TJPS. SOME PERIODS
OF REDUCED VIS AND LOW CEILINGS ARE ANTICIPATED. WINDS WILL PICK
UP AFTER 13-14Z, COMING OUT OF THE ENE AT THE SFC AT 9-11 KTS,
THEN GAINING A SE COMPONENT AFTER 15Z FROM 6-12 KFT.
MARINE
A FRONTAL BOUNDARY APPROACHING FROM THE WESTERN ATLANTIC WILL SLOWLY
LOOSEN THE PRESSURE GRADIENT ASSOCIATED WITH THE BROAD SURFACE HIGH
PRESSURE EXTENDING FROM THE EASTERN TO CENTRAL ATLANTIC. THIS WILL
RESULT IN WINDS BECOMING EAST TO NORTHEAST THROUGH TOMORROW AS AN
INDUCED SURFACE TROUGH ASSOCIATED WITH THE FRONTAL BOUNDARY MOVES IN.
THIS WILL ALSO INCREASE THE RISK OF SHOWERS AND EVEN THUNDERSTORMS
ACROSS THE REGIONAL WATERS TODAY THROUGH WEDNESDAY. A LONG-PERIOD
NORTHWESTERLY SWELL WILL REACH THE REGIONAL WATERS THIS WEEKEND,
LIKELY RESULTING IN HAZARDOUS SEAS ACROSS THE ATLANTIC WATERS AND
NORTHERN PORTIONS OF THE LOCAL PASSAGES.
BEACH FORECAST
LIFE-THREATENING RIP CURRENT CONDITIONS ARE POSSIBLE TODAY ALONG
BEACHES IN NORTHWESTERN AND NORTH-CENTRAL PUERTO RICO, AS WELL AS
ST. CROIX. BY LATE TONIGHT AND INTO TOMORROW, A WEAK NORTHWESTERLY
SWELL WILL REACH THE ATLANTIC WATERS, INCREASING BREAKING WAVE
HEIGHTS. THIS WILL, IN TURN, POSSIBLY ELEVATE THE RISK OF RIP
CURRENTS ALONG NORTHERN EXPOSED BEACHES.
RESIDENTS AND VISITORS IN THESE AREAS SHOULD HEED WARNINGS AND STAY
INFORMED THROUGH UPDATES FROM LOCAL AUTHORITIES.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM/AVIATION...ERG
LONG TERM/MARINE/BEACH...CVB
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