196
FXCA62 TJSJ 042054
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
454 PM AST TUE MAR 4 2025
SYNOPSIS
UNSTABLE WEATHER CONDITIONS WILL PERSIST THROUGH THE END OF THE
WORKWEEK DUE TO A SERIES OF TROUGHS CROSSING THE FORECAST AREA.
EXPECT SHOWER AND ISOLATED THUNDERSTORM ACTIVITY, PARTICULARLY
DURING THE AFTERNOON HOURS EACH DAY. A MORE STABLE WEATHER PATTERN
IS ANTICIPATED THIS WEEKEND, HOWEVER A NORTHWESTERLY SWELL WILL
REACH THE ATLANTIC WATERS RESULTING IN POTENTIAL HAZARDOUS SEAS
AND BEACH CONDITIONS DURING THE WEEKEND.
SHORT TERM...TONIGHT THROUGH THURSDAY
A MID-TO UPPER-LEVEL TROUGH WILL CONTINUE TO MOVE EASTWARD OVER THE
REGION THROUGH AT LEAST WEDNESDAY. THIS WILL CONTINUE TO PROVIDE
COLDER 500 MB TEMPERATURES AROUND MINUS 7/8 DEGREES C. THEREFORE,
THE POTENTIAL FOR HEAVY SHOWERS AND ISOLATED THUNDERSTORM
DEVELOPMENT WILL REMAIN HIGH THROUGH THIS PERIOD. AT THE LOWER
LEVELS, A COLD FRONT NORTH OF THE AREA AND AN APPROACHING TROUGH
FROM THE EAST WILL MAINTAIN LIGHT WINDS IN GENERAL. HOWEVER, WINDS
WILL ACQUIRE A MORE EAST-TO-NORTHEAST COMPONENT THROUGH THE REST OF
THE SHORT-TERM PERIOD. SLOW-MOVING SHOWERS WILL LEAD TO URBAN AND
SMALL-STREAM FLOODING. AFTERNOON CONVECTION CAN LINGER INTO THE
EVENING HOURS OVER LAND AREAS, MAINLY OVER PR, DUE TO THE LIGHTER
WINDS AND THE PROXIMITY OF THE UPPER-LEVEL TROUGH.
THE MID-TO UPPER-LEVEL TROUGH WILL DEPART BY THURSDAY, AND A RIDGE
WILL BE BUILT BEHIND IT. CONDITIONS ALOFT WILL NO LONGER FAVOR THE
FORMATION OF THUNDERSTORMS. STILL, SUFFICIENT SURFACE MOISTURE WILL
BRING ADDITIONAL SHOWERS ACROSS EASTERN PUERTO RICO AND THE U.S.
VIRGIN ISLANDS DURING THE EARLY MORNING HOURS. ACROSS WESTERN PR,
SHOWERS WILL DEVELOP DURING THE AFTERNOON HOURS DUE TO THE
COMBINATION OF THE AVAILABLE MOISTURE WITH DAYTIME HEATING AND THE
CONVERGENCE OF THE SEA BREEZE.
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
PREV DISCUSSION
/ISSUED 459 AM AST TUE MAR 4 2025/
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
(18Z TAFS)
ISOLATED TO SCATTERED SHRA WITH ISO TSTMS MAY LINGER THRU 04/23Z
OVER WESTERN PR, CAUSING TEMPO MVFR CONDS AT TJBQ. ACROSS THE USVI
AND THE EASTERN PR TERMINALS, SHRA EN ROUTE FM THE LEEWARD TERMINALS
MAY LEAD TO BRIEF MVFR CIGS THROUGH THE OVERNIGHT/EARLY MORNING
HOURS. OTHERWISE, VFR CONDS EXPECTED TO PREVAIL WITH SHRA/TSRA
DEVELOPING ONCE AGAIN NEAR TJSJ/TJBQ/TJPS AFT 05/16Z. THE 04/12Z
TJSJ SOUNDING INDICATED E-ENE WINDS UP TO 15 KT BLO FL050.
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 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
A MODERATE RISK OF RIP CURRENTS CONTINUES TONIGHT ACROSS NORTHERN
AND NORTHEASTERN BEACHES OF PUERTO RICO, CULEBRA, AND ST. CROIX,
WHILE A LOW RISK ELSEWHERE. A MODERATE RISK MEANS THAT LIFE-
THREATENING RIP CURRENTS ARE POSSIBLE IN THE SURF ZONE.
BY TOMORROW, A WEAK NORTHWESTERLY SWELL WILL REACH THE ATLANTIC
WATERS, INCREASING BREAKING WAVE HEIGHTS AND EXTENDING THE CURRENT
MODERATE RISK TO NORTHWESTERN PR AND ST. THOMAS AS WELL. RESIDENTS
AND VISITORS IN THESE AREAS ARE ENCOURAGED TO TAKE THE NECESSARY
PRECAUTIONS AND MONITOR THE FORECAST FOR ANY UPDATES.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM/AVIATION/MARINE...DS/LIS
LONG TERM...CVB
PUBLIC/BEACH FORECAST...YZR
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page