196
FXCA62 TJSJ 032050
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
450 PM AST MON MAR 3 2025
SYNOPSIS
A UNSTABLE WEATHER PATTERN IS FORECAST FOR THE UPCOMING DAYS WITH
AN UPPER LEVEL TROUGH AND COLDER TEMPERATURES AT THE 500 MB.
THEREFORE, FROM LATE TUESDAY INTO WEDNESDAY, RESIDENTS CAN EXPECT
SHOWER ACTIVITY IN THE LOCAL WATERS FOR THE MORNING AND EVENING
HOURS WITH SHOWERS AND ISOLATED THUNDERSTORMS IN THE AFTERNOON,
ESPECIALLY OVER THE INTERIOR SECTIONS OF PUERTO RICO.
SHORT TERM...TODAY THROUGH WEDNESDAY
WEATHER CONDITIONS WILL CHANGE FROM A DRIER TO A WETTER PATTERN
THROUGH THE SHORT-TERM FORECAST. LIGHT WINDS FROM THE SOUTHEAST AT
10 KNOTS OR LESS WILL CONTINUE TO PREVAIL THROUGH THE REST OF THE
DAY, IN RESPONSE TO A SURFACE HIGH PRESSURE OVER THE EASTERN
ATLANTIC AND A MID TO UPPER-LEVEL TROUGH, ALONG WITH ITS ASSOCIATED
COLD FRONT, LOCATED TO THE NORTHWEST OF THE REGION. AS THESE SYSTEMS
WEAKEN THE PRESSURE GRADIENT, THEY WILL ALSO MAKE CONDITIONS ALOFT
MORE CONDUCIVE TO THE FORMATION OF SHOWERS. THE PATCH OF MOISTURE
THAT IS MOVING ACROSS THE ISLANDS, WILL CONTINUE TO SUPPORT NEAR-
NORMAL PRECIPITABLE WATER CONTENT UP TO 1.60 INCHES THROUGH THE
OVERNIGHT HOURS. THEREFORE, THE DIURNALLY INDUCED AFTERNOON SHOWERS
WILL LINGER THROUGH THE OVERNIGHT HOURS OVER LAND AREAS, WITH UP TO
50% CHANCE OF PRECIPITATION, MAINLY OVER PUERTO RICO. THE RISK OF
URBAN AND SMALL STREAM FLOODING WILL REMAIN ELEVATED, AND THERE IS
POTENTIAL FOR QUICK WATER RISES ALONG SMALL STREAMS AND MUDSLIDES AS
WELL. CURRENTLY, CONDITIONS ARE NOT VERY FAVORABLE FOR THUNDERSTORMS
SINCE TEMPERATURES AT 500 MB ARE STILL WARMER THAN NORMAL, BUT
ISOLATED LIGHTNING STRIKES CANNOT BE RULED OUT.
ON TUESDAY, A SURFACE TROUGH WILL APPROACH, INCREASING THE FREQUENCY
OF SHOWERS FOR THE U.S. VIRGIN ISLANDS, VIEQUES, AND CULEBRA.
AFTERNOON THUNDERSTORMS ARE ALSO EXPECTED FOR THE INTERIOR, WEST,
AND NORTHWEST PUERTO RICO. A KEY DIFFERENCE ON TUESDAY IS THAT MID-
LEVEL TEMPERATURES WILL COOL DOWN, MAKING IT MORE LIKELY TO SEE
LIGHTNING ASSOCIATED WITH THE STRONGER SHOWERS.
BY WEDNESDAY, INSTABILITY WILL PERSIST, BUT THERE IS UNCERTAINTY
REGARDING WHERE AFTERNOON SHOWERS WILL DEVELOP. LOW-LEVEL WINDS WILL
HELP INITIATE CONVECTION IN THE INTERIOR, AS IS TYPICAL, BUT THE
MOVEMENT OF THESE SHOWERS WILL DEPEND ON THEIR VERTICAL GROWTH. IF
THEY REMAIN SHALLOW, A NORTH-NORTHWESTERLY MOVEMENT IS EXPECTED;
HOWEVER, IF THEY ARE INFLUENCED BY MID-LEVEL WINDS, THEY ARE LIKELY
TO MOVE SOUTHWARD. THE FORECAST REFLECTS A COMPROMISE BETWEEN THESE
POSSIBILITIES, SHOWING A WIDESPREAD PROBABILITY OF PRECIPITATION OF
30-50% ACROSS MOST OF PUERTO RICO, WITH HIGHER CHANCES OF 50-70% FOR
THE NORTHWEST CORNER.
LONG TERM...THURSDAY THROUGH MONDAY...FROM PREVIOUS DISCUSSION
BY THURSDAY, THE UPPER LEVEL TROUGH WILL BE EAST-NORTHEAST OF THE
ISLANDS AND WILL CONTINUE TO MOVE AWAY FROM THE ISLANDS. TO START
THE LONG TERM PERIOD, AT SURFACE LEVEL, A HIGH PRESSURE SYSTEM WILL
BE OVER THE CENTRAL ATLANTIC, WHILE A FRONTAL LOW MOVES INTO THE
EASTERN ATLANTIC. CURRENT MODEL GUIDANCE SUGGESTS THIS AND OTHER
FRONTAL LOWS MOVING INTO THE ATLANTIC DURING THE PERIOD ON THURSDAY,
FRIDAY AND MONDAY BEFORE HIGH PRESSURE BUILDS AND DOMINATES LATE
MONDAY. THIS WILL CAUSE CHANGES IN THE STEERING FLOW DURING THE
PERIOD, EAST-SOUTHEAST ON THURSDAY, EAST-SOUTHEAST TO EAST-NORTHEAST
ON FRIDAY (DUE TO AN APPROACHING COLD FRONT), EAST-NORTHEAST ON
SATURDAY AND THEN GRADUALLY VEERING DURING THE WEEKEND TO EAST-
SOUTHEAST LATE SUNDAY INTO MONDAY. THE PERIOD WILL START OFF WITH
PRECIPITABLE WATER (PWAT) VALUES AROUND 1.5 INCHES, MAINLY
MAINTAINED BY AN APPROACHING FRONTAL BOUNDARY WITH THE LINGERING
TRACES OF SAHARAN DUST DISSIPATING. MODEL DISCREPANCIES ARE PRESENT
REGARDING MOISTURE DURING THE WEEKEND, WITH ONE MORE INCLINED TO
PATCHES OF MOISTURE REACHING THE ISLAND DURING THAT TIME. THIS
INCLUDES SMALL POCKETS OF MOISTURE WITH PWAT VALUES AROUND 1.4 TO
1.5 INCHES REACHING THE ISLANDS. AVAILABLE MOISTURE SHOULD REMAIN
BELOW 750 MB THURSDAY THROUGH SATURDAY, AND BELOW 850 MB BY SUNDAY
AND MONDAY. AS THE FRONT APPROACHES THE REGION TO END THE WORKWEEK,
WINDS WILL DECREASE TO BECOME LIGHT AND VARIABLE, THIS WILL RESULT
IN SLOW AND LINGERING SHOWERS, ELEVATING THE EXCESSIVE RAINFALL RISK.
DURING THE PERIOD, THE DIURNAL PATTERN WILL VARY DEPENDING ON THE
STEERING FLOW. THIS INCLUDES, OVERNIGHT AND EARLY MORNING SHOWERS
STEERED TOWARDS WINDWARD SECTORS OF THE ISLANDS WHILE AFTERNOON
CONVECTION WILL FOCUS OVER THE INTERIOR TO EITHER NORTHWESTERN
(UNDER SOUTHEAST FLOW) OR SOUTHWESTERN (UNDER NORTHEAST FLOW) PR
DEPENDING ON THE STEERING FLOW THAT DAY. 925 MB TEMPERATURES WILL BE
UP TO ABOVE NORMAL VALUES DURING THE PERIOD, ESPECIALLY ON DAYS WITH
EAST-SOUTHEAST TO SOUTHEAST FLOW.
AVIATION
(18Z TAFS)
SHRA OVER WESTERN PR MAY LINGER THROUGH THE EVENING HOURS, CAUSING
MVFR CIGS AT TJBQ. VFR CONDS EXPECTED ACROSS THE REST OF THE
TERMINALS THRU AT LEAST 04/13Z. THE 03/12Z TJSJ SOUNDING INDICATED
ESE WINDS AT LESS THAN 10 KT BLO FL100.
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
PROMOTE EAST-SOUTHEAST WINDS TODAY AND TONIGHT. WINDS WILL BACK TO
BECOME 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 LATE TONIGHT THROUGH WEDNESDAY.
BEACH FORECAST
A MODERATE RIP OF RIP CURRENTS WILL BE PRESENT AT THE EASTERNMOST
BEACHES OF ST. CROIX, LIFE-THREATENING RIP CURRENTS ARE POSSIBLE
IN THE SURF ZONE. FOR TOMORROW INTO THE REST OF THE WEEK, A
MODERATE RISK OF RIP CURRENTS WILL BE IN EFFECT FOR THE NORTH-
FACING BEACHES OF PUERTO RICO, CULEBRA AND THE USVI. INCREASING
IN THE BREAKING WAVES IS FORECAST FOR THE UPCOMING WEEKEND.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM & AVIATION...DS
LONG TERM....MRR
MARINE & BEACH FORECAST...LIS
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