551
FXCA62 TJSJ 031857
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
257 PM AST SAT MAY 3 2025
SYNOPSIS
AN UNSTABLE AND WET WEATHER PATTERN WILL PERSIST FOR TONIGHT;
THEREFORE, THE FLOOD WATCH WILL REMAIN IN EFFECT UNTIL 8 PM AST. A
SLIGHT IMPROVEMENT IS FORECAST FOR TOMORROW; HOWEVER, THE ACTUAL
SOIL CONDITIONS AND THE ADDITIONAL RAINFALL ACCUMULATIONS WILL
RESULT IN URBAN AND SMALL-STREAM FLOODING.
SHORT TERM...TONIGHT THROUGH THURSDAY
AN ACTIVE MORNING WAS OBSERVED ACROSS THE NORTHERN MUNICIPALITIES,
WHERE SHOWERS AND THUNDERSTORMS AFFECTED MAINLY THE NORTH-CENTRAL
TO NORTHEASTERN REGIONS OF PUERTO RICO. RAINFALL ACCUMULATION
ESTIMATES FROM DOPPLER RADAR RANGED BETWEEN 4 AND 5 INCHES OVER
DORADO AND VEGA ALTA. WEATHER CONDITIONS IMPROVED SLIGHTLY
AFTERWARD, BUT QUICK-MOVING SHOWERS DEVELOPED OVER THE
NORTHWESTERN SECTIONS OF THE ISLAND. STRONG SHOWERS AND
THUNDERSTORMS WERE OBSERVED OVER LARES AND SAN SEBASTIAN, WHERE
REPORTS OF HAIL WERE RECEIVED AROUND 1 PM. RAINFALL ACCUMULATIONS
WITH THE PEAK OF THE SHOWERS FLUCTUATED BETWEEN 2 2 TO 3 INCHES
AROUND THE WESTERN INTERIOR. DAYTIME TEMPERATURES REMAINED IN THE
MID 80S ALONG THE COASTAL AREAS AND IN THE UPPER 70S TO LOWER 80S
ALONG THE MOUNTAINS.
SHOWER ACTIVITY WILL PERSIST ALONG THE MOUNTAINS FOR THE REST OF
THE AFTERNOON INTO THE NIGHT HOURS. GIVEN THE EXPECTED CONDITIONS,
THE FLASH FLOOD WATCH REMAINS IN EFFECT FOR PUERTO RICO UNTIL 8
PM TONIGHT. THEREFORE, RESIDENTS CAN EXPECT A MORE STABLE WEATHER
PATTERN DURING THE NIGHT HOURS WITH AN INCREASE IN SHOWERS EARLY
ON SUNDAY ALONG EASTERN SECTIONS.
MODEL GUIDANCE AND DERIVED IMAGERY FROM THE GOES SATELLITE
INDICATE THAT PRECIPITABLE WATER (PWAT) VALUES WILL REMAIN
ANOMALOUSLY HIGH, BETWEEN 2.05 INCHES, NEAR THE +2 STANDARD
DEVIATION THRESHOLD. A GRADUAL DRYING TREND IS ANTICIPATED
BEGINNING ON SUNDAY, WITH PWAT VALUES DECREASING TO AROUND 1.8
INCHES, BUT REMAINING ABOVE NORMAL THROUGH THE WEEKEND. MID-LEVELS
REMAIN FAVORABLE FOR DEEP CONVECTION, WITH 500 MB TEMPERATURES
BETWEEN -8°C AND -10°C CONTINUING TO SUPPORT THUNDERSTORM
DEVELOPMENT WITH THE POTENTIAL FOR HEAVY RAINFALL.
ALTHOUGH THE BROAD UPPER-LEVEL TROUGH BEGINS TO SHIFT EASTWARD
INTO THE ATLANTIC BY SUNDAY, LOCALIZED CONVECTIVE DEVELOPMENT WILL
PERSIST DUE TO DIURNAL HEATING, PARTICULARLY ACROSS THE
CORDILLERA CENTRAL, EL YUNQUE VICINITY, AND WESTERN INTERIOR.
SOILS REMAIN HEAVILY SATURATED, INCREASING THE RISK OF FLASH
FLOODING, RAPID RIVER RISES, AND MUDSLIDES, ESPECIALLY WITH ANY
TRAINING OR SLOW-MOVING STORMS. BY MONDAY, THE MODEL CONSENSUS
SUPPORTS FURTHER DRYING IN THE MID-AND UPPER-LEVELS, AS 700–500 MB
RELATIVE HUMIDITY TRENDS ARE LOWER NEAR CLIMATOLOGICAL NORMALS.
HOWEVER, LOCAL EFFECTS WOULD ALLOW THE DEVELOPMENT OF ISOLATED
AFTERNOON THUNDERSTORMS, PRIMARILY OVER INTERIOR AND NORTHWESTERN
PUERTO RICO. THE U.S. VIRGIN ISLANDS CAN EXPECT MORE STABLE
CONDITIONS WITH PASSING SHOWERS.
LONG TERM...TUESDAY THROUGH SATURDAY
FROM PREVIOUS
DISCUSSION...
A DEEP LAYER LOW PRESSURE NORTH OF THE AREA AND A SERIES OF
SURFACE INDUCED TROUGHS WILL PROMOTE A EAST TO NORTHEAST WIND FLOW
FOR THE FIRST HALF OF THE PERIOD. THEN, WINDS ARE EXPECTED TO
BECOME FROM THE SOUTHEAST BY THE END OF THE WORKWEEK AS THE LOW
PRESSURE SHIFTS TOWARDS THE WEST. ABUNDANT LOW-LEVEL MOISTURE WILL
PREDOMINATE OVER THE LONG TERM- PERIOD WITH PRECIPITABLE WATER
VALUES BETWEEN 1.60 TO 1.75 INCHES. DURING THIS PERIOD THE 500 MB
TEMPERATURES WILL DROP INTO THE -7 TO -9 DEGREES CELSIUS,
SUGGESTING THE POTENTIAL TO SUPPORT CONVECTIVE ACTIVITY ACROSS THE
REGION. THROUGHOUT THE WEEK, INSTABILITY WILL PERSIST AS THE LOW
PRESSURE AND THE INDUCED SURFACE TROUGH PATTERN PREVAIL IN THE
REGION. THEREFORE, THERE IS AN INCREASED POTENTIAL TO OBSERVE
AFTERNOON CONVECTIVE ACTIVITY ALONG PORTIONS OF THE INTERIOR AND
WESTERN PUERTO RICO EACH DAY. WITH THE RAINFALL EVENTS FROM
PREVIOUS DAYS, ABOVE- NORMAL STREAMFLOWS AND SATURATED SOILS, THE
FLOOD THREAT REMAINS ELEVATED. THE LATEST MODEL GUIDANCES ARE
SUGGESTING A CHANGE IN THE WEATHER PATTERN BY THE END OF THE WEEK
INTO THE WEEKEND WITH THE ENTRANCE OF DRIER AIR INTO THE AREA.
SEASONAL TEMPERATURES ARE ANTICIPATED TO PREVAIL FOR THE REST OF
THE FORECAST PERIOD, WITH THE HEAT RISK REMAINING LOW.
AVIATION
(18Z)
MVFR AND IFR CONDITIONS WILL BE PRESENT UNTIL 03/23Z FOR MOST OF
THE TAF SITES WITH LOWER CEILINGS AND REDUCTION IN VIS DUE TO
SHRA/TS. WINDS WILL CONTINUE FROM THE E, AND AT 3 KM FROM THE E-SE
UNTIL 03/00Z, DIMINISHING AND BECOMING MORE VRB DURING THE NIGHT.
VCSH/-RA ARE POSSIBLE OVER THE NIGHT HOURS ALONG THE USVI TAF
SITES. FOR TOMORROW, ANOTHER ROUND OF -SHRA IS FORECAST FOR TJSJ
AT AROUND 04/15Z.
MARINE
A BROAD SURFACE OF HIGH PRESSURE OVER THE WESTERN ATLANTIC WILL
CONTINUE TO RESULT IN AN EASTERLY WIND FLOW ACROSS THE REGION,
WITH WINDS UP TO 15 KNOTS. SEAS AROUND THE LOCAL WATERS WILL
REMAIN BETWEEN 3 TO 5 FEET FOR THE UPCOMING DAYS. SHOWER AND
THUNDERSTORM ACTIVITY IS FORECAST ALONG THE LOCAL WATERS RESULTING
IN LOCALIZE HIGH SEAS AND THUNDER ACTIVITY.
BEACH FORECAST
THERE IS A MODERATE RISK OF RIP CURRENTS FOR THE EXPOSED BEACHES
OF NORTHERN PUERTO RICO, CULEBRA, AND THE U.S. VIRGIN ISLANDS.
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 NEXT
WEEK.
SJU WATCHES/WARNINGS/ADVISORIES
PR...FLOOD WATCH UNTIL 8 PM AST THIS EVENING FOR PRZ001>013.
VI...NONE.
AM...NONE.
SHORT TERM...LIS
LONG TERM....MNG
AVIATION...LIS
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