093
FXCA62 TJSJ 060909
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
509 AM AST THU MAR 6 2025
SYNOPSIS
MARGINAL INSTABILITY AND ABOVE NORMAL MOISTURE WILL RESULT IN
ACTIVE AFTERNOONS TODAY AND TOMORROW. THE WEAK STEERING WINDS WILL
ENHANCE RAINFALL ACCUMULATIONS, INCREASING THE RISK OF URBAN AND
SMALL- STREAM FLOODING, AS WELL AS QUICK RIVER RISES AND WATER
SURGES IN SOME RIVERS. THIS WEEKEND, CONDITIONS WILL SHIFT,
BECOMING SIGNIFICANTLY MORE STABLE.
SHORT TERM...TODAY THROUGH SATURDAY
PARTLY CLOUDY SKIES PREVAILED ACROSS PUERTO RICO AND THE U.S. VIRGIN
ISLANDS OVERNIGHT. SHOWERS WERE OBSERVED OVER THE REGIONAL WATERS
AND ACROSS THE NORTHERN AND EASTERN SECTIONS OF PUERTO RICO, WITH
SOME MOVING OVER THE SMALLER ISLANDS. DURING THE MORNING HOURS,
EXPECT SIMILAR ACTIVITY TO PERSIST ACROSS THE WINDWARD SECTORS.
CURRENT SATELLITE-DERIVED PRECIPITABLE WATER (PWAT) VALUES INDICATE
AN AREA OF ABOVE-NORMAL MOISTURE, WITH VALUES RANGING FROM
APPROXIMATELY 1.6 TO 1.9 INCHES, LOCATED OVER AND EAST-SOUTHEAST OF
THE ISLANDS. THIS MOISTURE IS ASSOCIATED WITH A SURFACE-INDUCED
TROUGH, WITH ITS AXIS POSITIONED BETWEEN THE U.S. VIRGIN ISLANDS AND
THE NORTHERN LEEWARD ISLANDS. AN APPROACHING FRONTAL BOUNDARY, WITH
A SHEARLINE AHEAD OF IT, IS PROMOTING SOUTHEASTERLY WINDS ACROSS THE
ISLANDS. STEERED BY THESE LOW-LEVEL SOUTHEASTERLY WINDS, THE SURFACE-
INDUCED TROUGH WILL CONTINUE TO MOVE IN TODAY WHILE WEAKENING. AS
THE AFOREMENTIONED SHEARLINE ADVANCES, WINDS WILL GRADUALLY SHIFT TO
A MORE SOUTHERLY DIRECTION LATER THIS AFTERNOON.
BY EARLY FRIDAY, AS THE SHEAR LINE CONTINUES TO APPROACH, A COL
REGION WILL MOVE OVER THE ISLANDS, CAUSING WIND SPEEDS TO DROP
SIGNIFICANTLY. A BRIEF NORTHEASTERLY WIND COMPONENT IS EXPECTED
DURING THE AFTERNOON AS THE COL EXITS THE AREA. DURING THIS PERIOD,
PWAT VALUES WILL REMAIN AT NEAR-NORMAL LEVELS. SUBSEQUENTLY, A
NORTHEASTERLY STEERING WIND FLOW WILL ESTABLISH ITSELF AS THE
FRONTAL BOUNDARY STALLS TO THE NORTH, BRINGING BELOW-NORMAL MOISTURE
CONTENT TO THE REGION. MOST AVAILABLE MOISTURE WILL REMAIN BELOW
500–600 MB TODAY AND TOMORROW, AS IT COMBINES WITH TROUGHINESS
ALOFT. AS A MID-LEVEL RIDGE GRADUALLY BUILDS ACROSS THE REGION BY
THE WEEKEND, AVAILABLE MOISTURE WILL BECOME CONFINED BELOW 850 MB,
LEADING TO MORE STABLE WEATHER CONDITIONS.
TODAY, UNDER A SOUTHERLY WIND FLOW, ABOVE-NORMAL HIGH TEMPERATURES
ARE EXPECTED ACROSS PARTS OF THE ISLANDS, WITH NORTH-CENTRAL PUERTO
RICO EXPERIENCING HIGHER-THAN-USUAL APPARENT TEMPERATURES. THE 925
MB TEMPERATURES ARE FORECAST TO REACH NEARLY TWO STANDARD
DEVIATIONS ABOVE NORMAL TODAY.
IN THE AFTERNOON, DIURNAL HEATING, SEA BREEZE CONVERGENCE, AND LOCAL
EFFECTS WILL PROMOTE CONVECTIVE ACTIVITY, PRIMARILY OVER THE
INTERIOR AND NORTH-CENTRAL MUNICIPALITIES OF PUERTO RICO. ISOLATED
THUNDERSTORMS CANNOT BE RULED OUT. ON FRIDAY, SIMILAR CONDITIONS ARE
EXPECTED; HOWEVER, THE WEAK NORTHEASTERLY STEERING WIND FLOW WILL
SHIFT AFTERNOON CONVECTION TOWARD THE INTERIOR AND SOUTHWESTERN
PORTIONS OF PUERTO RICO. THE WEAK STEERING WINDS WILL ENHANCE
RAINFALL ACCUMULATIONS IN THESE AREAS, INCREASING THE RISK OF URBAN
AND SMALL-STREAM FLOODING, AS WELL AS QUICK RIVER RISES AND WATER
SURGES IN SOME RIVERS. BY SATURDAY, CONDITIONS WILL SHIFT, BECOMING
SIGNIFICANTLY MORE STABLE.
LONG TERM...SUNDAY THROUGH THURSDAY
THE LONG-TERM PERIOD WILL BE MAINLY CHARACTERIZED BY MORE STABLE
CONDITIONS. A MID-TO UPPER-LEVEL RIDGE WILL REMAIN IN PLACE AT LEAST
THROUGH TUESDAY OR MID WEEK, SUPPRESSING DEEP CONVECTIVE DEVELOPMENT
ACROSS THE REGION. AT THE SURFACE, EAST-SOUTHEAST TRADE WINDS WILL
DOMINATE THROUGHOUT THE PERIOD DUE TO A BROAD SURFACE HIGH PRESSURE
SYSTEM ACROSS THE ATLANTIC. BASED ON THE LATEST MODEL GUIDANCE,
PRECIPITABLE WATER VALUES WILL REMAIN IN THE BELOW NORMAL RANGE
THROUGH AT LEAST TUESDAY. AS A RESULT, SHOWER ACTIVITY, IF ANY, IS
EXPECTED TO FOLLOW A MORE TYPICAL PATTERN, WHERE WE OBSERVE ISOLATED
SHOWERS MOVING ACROSS WINDWARD COASTAL AREAS DURING THE NIGHT AND
EARLY MORNING HOURS, FOLLOWED BY LOCALIZED SHALLOW CONVECTION
DEVELOPING ACROSS WESTERN AND INTERIOR SECTIONS OF PUERTO RICO IN
THE AFTERNOONS. AT THE MOMENT, NO SIGNIFICANT RAINFALL ACCUMULATIONS
OR WIDESPREAD FLOODING CONCERNS ARE EXPECTED. BY MIDWEEK ONWARDS,
PRECIPITABLE WATER VALUES ARE EXPECTED TO SLIGHTLY INCREASE TO
SEASONAL LEVELS AS PATCHES OF MOISTURE IN THE TRADES MOVE ACROSS THE
FORECAST AREA, AND A WEAK UPPER-LEVEL TROUGH AND ITS ASSOCIATED
FRONTAL BOUNDARY APPROACH THE CARIBBEAN FROM THE NORTHWEST.
OVERALL, A QUIET WEATHER PATTERN IS EXPECTED THROUGH MOST OF THE
PERIOD, WITH WEDNESDAY AND THURSDAY BEING THE DAYS WITH THE BEST
CHANCES OF RAIN, ESPECIALLY IN THE AFTERNOON HOURS ACROSS PORTIONS
OF WESTERN PUERTO RICO. HOWEVER, NO SIGNIFICANT FLOODING CONCERNS
ARE ANTICIPATED AT THIS TIME. DAYTIME TEMPERATURES ARE EXPECTED TO
REMAIN IN THE MID TO UPPER 80S ALONG COASTAL AND LOWER ELEVATION
AREAS, WHILE TEMPERATURES IN THE MOUNTAINS WILL RANGE FROM THE MID
70S TO LOWER 80S.
AVIATION
(06Z TAFS)
MAINLY VFR CONDITIONS WILL PREVAIL ACROSS ALL TAF SITES. HOWEVER,
SHRA/TSRA DEVELOPMENT COULD RESULT IN BRIEF MVFR CONDITIONS AT
TJBQ/TJSJ AND MTN TOP OBSC, FROM 17Z TO 22Z. SE (BCMG S) WINDS
BETWEEN 08-12 KT, WITH HIGHER GUSTS NEAR SHOWERS, BCMG CALM TO
LIGHT AND VARIABLE AFT 06/23Z.
MARINE
A FADING NORTHERLY SWELL WILL CONTINUE TO SPREAD ACROSS THE ATLANTIC
WATERS KEEPING WAVE HEIGHTS AROUND 5 TO 6 FEET THROUGH AT LEAST
TODAY. A FRONTAL BOUNDARY APPROACHING FROM THE WESTERN ATLANTIC WILL
CONTINUE TO WEAKEN THE PRESSURE GRADIENT ASSOCIATED WITH THE BROAD
SURFACE HIGH PRESSURE EXTENDING FROM THE EASTERN TO CENTRAL
ATLANTIC, RESULTING IN LIGHT TO MODERATE SOUTHERLY WINDS TODAY. BY
FRIDAY, WINDS WILL BECOME EVEN LIGHTER WHILE TURNING FROM THE
EAST TO NORTHEAST DUE TO THE INFLUENCE OF A COL REGION.
ADDITIONALLY, A LONG- PERIOD NORTHWESTERLY SWELL IS EXPECTED TO
ARRIVE NEXT SATURDAY, LIKELY DETERIORATING MARINE CONDITIONS
ACROSS THE ATLANTIC WATERS AND NORTHERN LOCAL PASSAGES.
BEACH FORECAST
THE ENERGY OF A FADING NORTHERLY SWELL IS STILL SPREADING ACROSS OUR
NORTHERN WATERS RESULTING IN BREAKING WAVES UP TO 6 FEET. AS A
RESULT, THE HIGH RIP CURRENT RISK REMAINS IN EFFECT TODAY THROUGH AT
LEAST THIS AFTERNOON FOR THE NORTHERN BEACHES OF PUERTO RICO, FROM
FAJARDO TO AGUADILLA. A MODERATE RISK IS PRESENT ACROSS THE
NORTHWESTERN BEACHES FOR PUERTO RICO, AS WELL AS IN VIEQUES,
CULEBRA AND THE U.S. VIRGIN ISLANDS. ALONG THE SOUTHERN BEACHES OF
PUERTO RICO, THE RISK REMAINS LOW, HOWEVER, LIFE-THREATENING RIP
CURRENTS OFTEN OCCUR IN THE VICINITY OF JETTIES, REEFS, AND PIERS.
RESIDENTS AND VISITORS ARE ENCOURAGED TO TAKE THE NECESSARY
PRECAUTIONS AND MONITOR THE FORECAST FOR ANY UPDATES. BY FRIDAY,
THE RISK IS EXPECTED TO REMAIN MODERATE, BUT LIKELY RETURN TO HIGH
BY SATURDAY ALONG THE NORTH COAST OF PUERTO RICO, CULEBRA AND
NORTHERN USVI DUE TO A STRONGER NORTHWESTERLY SWELL.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HIGH RIP CURRENT RISK THROUGH THIS AFTERNOON FOR PRZ001-002-005-
008.
VI...NONE.
AM...NONE.
SHORT TERM/AVIATION...CVB
LONG TERM/MARINE/BEACH...YZR
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