848
FXCA62 TJSJ 041813
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
213 PM AST SUN MAY 4 2025
SYNOPSIS
A SLIGHT IMPROVEMENT IN WEATHER CONDITIONS IS FORECAST FOR
TOMORROW INTO TUESDAY. ANOTHER UPPER-LEVEL FEATURE WILL MOVE INTO
THE LOCAL ISLANDS, INCREASING INSTABILITY FROM LATE TUESDAY INTO
WEDNESDAY.
SHORT TERM... TONIGHT THROUGH TUESDAY
A STALE MORNING PREVAILED ACROSS PUERTO RICO AND THE U.S. VIRGIN
ISLANDS, WITH PARTLY CLOUDY SKIES FOR MOST OF THE EAST SIDE AND
CLEAR SKIES FOR THE HALF WEST OF PR. CLOUDINESS DEVELOPED ACROSS
THE WESTERN INTERIOR IN THE EARLY MORNING HOURS WHEN SHOWERS WERE
NOTED ACROSS SOME INTERIOR MUNICIPALITIES AROUND AIBONITO AND
CAYEY. SHOWER ACTIVITY EXTENDED ALONG THE REST OF THE MOUNTAIN
MUNICIPALITIES AFFECTING AIBONITO, CAYEY, NARANJITO AND
NORTHWESTERN SECTIONS AS WELL. RAINFALL ACCUMULATION SO FAR RANGE
FROM 1 TO 3 INCHES. DAYTIME TEMPERATURES REMAINED IN THE UPPER
80S ALONG THE COASTAL AREAS AND IN THE UPPER 70S TO LOWER 80S
ALONG THE MOUNTAINS.
A MOIST AND MODERATELY UNSTABLE WEATHER PATTERN WILL CONTINUE TO
AFFECT PUERTO RICO AND THE U.S. VIRGIN ISLANDS THROUGH TUESDAY.
FOR MONDAY, PRECIPITABLE WATER VALUES WILL REMAIN BETWEEN 1.5 AND
1.7 INCHES, WHICH IS NEAR TO SLIGHTLY ABOVE NORMAL. THIS WILL
SUPPORT PERIODS OF ISOLATED TO SCATTERED PASSING SHOWERS DURING
THE EARLY MORNING HOURS, ESPECIALLY ACROSS THE U.S. VIRGIN ISLANDS
AND THE EASTERN SLOPES OF PUERTO RICO. IN THE AFTERNOON, THE
COMBINATION OF DIURNAL HEATING, LINGERING MID-LEVEL MOISTURE, AND
MODEST INSTABILITY WILL FAVOR THE DEVELOPMENT OF SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS, MAINLY ACROSS THE INTERIOR AND WESTERN
MUNICIPALITIES OF PUERTO RICO. ELEVATED RELATIVE HUMIDITY VALUES
IN THE 700–500 MB LAYER WILL SUPPORT CONVECTIVE ACTIVITY AND
LOCALIZED RAINFALL ACCUMULATIONS. ISOLATED URBAN AND SMALL STREAM
FLOODING CANNOT BE RULED OUT IN AREAS OF PERSISTENT RAINFALL.
BY TUESDAY, MODEL GUIDANCE SUGGESTS A SHIFT IN THE SYNOPTIC
PATTERN AS THE UPPER-LEVEL TROUGH (500 TO 250 MB) CONTINUES TO
MOVE EASTWARD INTO THE CENTRAL ATLANTIC. THIS WILL PLACE THE LOCAL
ISLANDS UNDER THE SUBSIDENT, MORE STABLE SIDE OF THE FEATURE. AS
A RESULT, CONDITIONS ALOFT ARE EXPECTED TO GRADUALLY STABILIZE,
WITH DECREASING RELATIVE HUMIDITY VALUES AND A DOWNWARD TREND IN
PRECIPITABLE WATER CONTENT. DESPITE THIS, THE COMBINATION OF
DAYTIME HEATING AND SEA BREEZE CONVERGENCE WILL STILL RESULT IN
AFTERNOON SHOWER DEVELOPMENT, PARTICULARLY ACROSS INTERIOR AND
WESTERN PUERTO RICO. HOWEVER, OVERALL COVERAGE AND INTENSITY OF
RAINFALL IS EXPECTED TO BE LOWER THAN MONDAY. WINDS AT THE SURFACE
AND 925 MB WILL BECOME LIGHTER AND MORE SOUTHEASTERLY AS THE
PRESSURE GRADIENT WEAKENS, FURTHER SUPPORTING LOCALIZED
CONVERGENCE ZONES THAT COULD STILL TRIGGER BRIEF SHOWERS.
LONG TERM...WEDNESDAY THROUGH SUNDAY
FROM PREVIOUS DISCUSSION...
A LOW PRESSURE SYSTEM NORTH OF THE AREA WILL PROMOTE EAST TO
NORTHEASTERLY WINDS TROUGH THE FIRST HALF OF THE LONG TERM PERIOD.
HOWEVER, WINDS ARE EXPECTED TO SHIFT FROM THE SOUTHEAST AS THE
LOW PRESSURE MIGRATES WESTWARDS OVER THE ATLANTIC. THE LATEST
MODEL GUIDANCES HAVE BEEN CONSISTENT WITH PREVIOUS MODEL RUNS ON
THE ENTRANCE OF A RELATIVELY DRIER AIRMASS INTO THE REGION,
PROMOTING STABLE CONDITIONS OVER THE ISLANDS. THE PRECIPITABLE
WATER CONTENT (PWAT) WILL REMAIN WITHIN NORMAL CLIMATOLOGICAL
VALUES OF 1.6 TO 1.8 INCHES THROUGH MUCH OF THE FORECAST PERIOD.
NONETHELESS, AT THE 500 MB LEVEL THE TEMPERATURES WILL DROP INTO
-9 TO -10 DEGREES CELSIUS SUGGESTING THE POTENTIAL TO SUPPORT
CONVECTIVE ACTIVITY DURING THE AFTERNOON HOURS OVER THE ISLANDS.
UNDER THE AFOREMENTIONED PATTERN, TYPICAL SEASONAL WEATHER
CONDITIONS ARE ANTICIPATED WITH SUNNY TO PARTLY CLOUDY MORNINGS
ACROSS PUERTO RICO AND THE U.S. VIRGIN ISLANDS. THEN, FOLLOWED BY
AFTERNOON CONVECTIVE ACTIVITY OVER PORTIONS OF CENTRAL AND WESTERN
PUERTO RICO EACH AFTERNOON. WITH THE RAINFALL ACTIVITY FROM PREVIOUS
DAYS/WEEKS, IT IS IMPORTANT TO REMEMBER TO STAY WEATHER ALERT DUE TO
ABOVE-NORMAL STREAMFLOWS AND SATURATED SOILS THAT MAY RESULT IN
LOCALIZED FLOODING ACROSS PORTIONS OF PUERTO RICO. THE 925 MB
TEMPERATURES WILL REMAIN AT NORMAL OR BELOW-NORMAL VALUES DURING THE
WEEK. HIGHS ARE ANTICIPATED IN THE LOW TO MID 80S ACROSS THE
COASTAL AND URBAN AREAS, AND IN THE MID TO UPPER 70S.
AVIATION
(18Z)
SHRA/TSRA WILL INDUCE MVFR AND BRIEFLY IFR CONDITIONS ALONG MOST
OF THE TAF SITES AT AROUND 04/18Z TO 04/23Z. THIS CONDITIONS WILL
RESULT IN LOWER CEILINGS AND REDUCTION IN VIS. WINDS WILL
CONTINUE FROM THE E-SE FROM 0 TO 3 KM, DIMINISHING AT 8 KNOTS
FROM 04/23Z. VCSH ARE POSSIBLE ACROSS TIST AND TISX DURING THE
NIGHT HOURS.
MARINE
A BROAD SURFACE HIGH PRESSURE EXTENDING FROM THE WESTERN INTO THE
CENTRAL ATLANTIC, IN COMBINATION WITH AN INDUCED SURFACE TROUGH
JUST NORTHEAST OF THE REGION, WILL RESULT IN A STEADY EASTERLY
WIND FLOW ACROSS THE LOCAL WATERS. THEREFORE, SEAS WILL REMAIN
BETWEEN 3 TO 5 FEET WITH WINDS UP TO 15 KNOTS. THUNDERSTORMS
ACTIVITY IS EXPECTED ALONG THE LOCAL WATERS FOR TONIGHT RESULTING
IN HIGHER SEAS.
BEACH FORECAST
THERE IS A MODERATE RISK OF RIP CURRENTS FOR THE BEACHES OF PUERTO
RICO FROM AGUADILLA TO FAJARDO. BEACHGOERS MUST EXERCISE CAUTION
DUE TO POSSIBLE LIFE- THREATENING RIP CURRENTS ALONG THE SURF ZONE
AND STAY WEATHER ALERT. THE RIP CURRENT RISK IS STILL EXPECTED TO
GRADUALLY DECREASE BY EARLY THIS WEEK.
SJU WATCHES/WARNINGS/ADVISORIES
PR...FLOOD WATCH UNTIL 8 PM AST THIS EVENING FOR PRZ001>013.
VI...NONE.
AM...NONE.
SHORT TERM, AVIATION & MARINE...LIS
LONG TERM....GRS
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