198
FXCA62 TJSJ 210704
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
304 AM AST FRI AUG 21 2026
...NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER...
KEY MESSAGES
ISSUED AT 258 AM AST FRI AUG 21 2026
* A HEAT ADVISORY IS IN EFFECT FROM 10 AM TO 5 PM DUE TO HOT
TEMPERATURES AND HEAT INDICES BETWEEN 108 AND 111 DEGREES.
SIMILAR CONDITIONS ARE FORECAST FROM SATURDAY INTO SUNDAY WITH
A HEAT THREAT ACROSS THE URBAN AND COASTAL AREAS.
* A STABLE DAY IS EXPECTED, WITH MOSTLY CLEAR SKIES AND LIMITED
SHOWER ACTIVITY. HOWEVER, RAINFALL ACCUMULATIONS ARE NOT
EXPECTED TO RESULT IN FLOODING THREAT.
* A MORE VARIABLE WEATHER PATTERN IS EXPECTED FROM SATURDAY INTO
SUNDAY, WITH A SLIGHT INCREASE IN THE FREQUENCY OF PASSING
SHOWERS.
* SAHARAN DUST PARTICLES WILL REMAIN IN PLACE AT LEAST THROUGH
THIS EVENING.
* A LOW TO MODERATE RISK OF RIP CURRENTS IS EXPECTED FOR THE UPCOMING
DAYS.
SHORT TERM(TODAY THROUGH SUNDAY)
ISSUED AT 258 AM AST FRI AUG 21 2026
DURING THE OVERNIGHT HOURS, MOSTLY CLEAR SKIES WERE OBSERVED
ACROSS PUERTO RICO. HOWEVER, SOME HIGH-LEVEL CLOUDINESS WAS
OBSERVED OVER PORTIONS OF THE ISLAND MUNICIPALITIES OF VIEQUES AND
CULEBRA, AS WELL AS ACROSS THE U.S. VIRGIN ISLANDS, ASSOCIATED
WITH A CUTOFF LOW IN THE UPPER LEVELS OVER THE REGION. IN TERMS OF
RAINFALL, NO SHOWER ACTIVITY WAS OBSERVED OVERNIGHT ACROSS THE
FORECAST AREA (CWA). MINIMUM TEMPERATURES WERE IN THE LOW 80S
ACROSS COASTAL AND URBAN AREAS AND IN THE MID 70S ACROSS THE
HIGHER ELEVATIONS. WINDS WERE GENERALLY FROM THE EAST AT SPEEDS UP
TO 10 MPH, WITH SOME VARIATIONS ASSOCIATED WITH THE LAND BREEZE
ALONG COASTAL AREAS.
FOR THE REST OF THE MORNING, CONDITIONS SIMILAR TO THOSE OBSERVED
OVERNIGHT ARE EXPECTED TO PREVAIL, BUT WITH LESS HIGH- TO MID-
LEVEL CLOUDINESS AS IT GRADUALLY MOVES NORTH OF THE REGION. AT THE
UPPER LEVELS, THE CUTOFF LOW WILL CONTINUE TO FAVOR SOME HIGH-
LEVEL CLOUDINESS DURING THE EARLY MORNING HOURS AS IT GRADUALLY
SHIFTS NORTH OF THE CWA. AT THE SURFACE, A TRADE WIND PATTERN WILL
PREVAIL UNDER THE INFLUENCE OF A SURFACE HIGH PRESSURE OVER THE
ATLANTIC, PROMOTING GENERALLY EASTERLY WINDS ACROSS THE REGION.
MEANWHILE, A RELATIVELY DRY AIR MASS, ACCOMPANIED BY MODERATE TO
LOCALLY HIGH CONCENTRATIONS OF SAHARAN DUST PARTICLES, WILL
CONTINUE TO DOMINATE THE AREA. AS A RESULT, ANOTHER HAZY AND HOT
DAY IS EXPECTED, WITH LIMITED SHOWER ACTIVITY. WARM TEMPERATURES
AND ELEVATED HEAT INDICES COULD EXACERBATE HEAT-RELATED IMPACTS,
PARTICULARLY AMONG VULNERABLE COMMUNITIES AND PEOPLE EXPOSED TO
THE SUN FOR PROLONGED PERIODS. DUE TO THESE CONDITIONS, A HEAT
ADVISORY IS IN EFFECT FOR THE COASTAL AND URBAN AREAS OF PUERTO
RICO, INCLUDING THE CAGUAS URBAN AREA AND NEARBY MUNICIPALITIES.
BY SATURDAY, THE WEATHER PATTERN WILL BEGIN TO CHANGE ACROSS THE
REGION AS AN INCREASE IN MOISTURE ASSOCIATED WITH PATCHES OF
MOISTURE FROM A LOW-PRESSURE SYSTEM LOCATED WELL NORTH OF THE
ISLANDS OVER THE NORTH-CENTRAL ATLANTIC IS ADVECTED INTO THE AREA
BY THE EASTERLY TRADE WINDS, WHILE SAHARAN DUST CONCENTRATIONS
GRADUALLY DECREASE. THEREFORE, AN INCREASE IN THE POTENTIAL FOR
PASSING SHOWERS, RESULTING IN A MORE VARIABLE WEATHER PATTERN, IS
FORECAST FROM SATURDAY ONWARD. DESPITE THE EXPECTED INCREASE IN
SHOWER ACTIVITY, SIGNIFICANT RAINFALL ACCUMULATIONS ARE NOT
ANTICIPATED, AND THE FLOODING POTENTIAL SHOULD REMAIN LIMITED AND
MAINLY FOCUSED ACROSS WESTERN PUERTO RICO WITH THE STRONGEST
AFTERNOON SHOWERS. BY SUNDAY, THE SURFACE PATTERN WILL REMAIN
RELATIVELY SIMILAR, WITH PATCHES OF MOISTURE MOVING IN AND OUT OF
THE REGION UNDER A PREVAILING SOUTHEASTERLY WIND FLOW. THIS WILL
CONTINUE TO SUPPORT PERIODS OF PASSING SHOWERS ACROSS THE ISLANDS,
PARTICULARLY ACROSS WINDWARD AREAS DURING THE MORNING HOURS,
FOLLOWED BY AFTERNOON SHOWER DEVELOPMENT MAINLY ACROSS
NORTHWESTERN PUERTO RICO. OVERALL, A MORE VARIABLE WEATHER PATTERN
IS EXPECTED DURING THE WEEKEND, WITH PERIODS OF PASSING SHOWERS
ALTERNATING WITH PERIODS OF DRIER CONDITIONS. DURING THESE DAYS,
THE HEAT THREAT WILL REMAIN ACROSS COASTAL AND URBAN AREAS, WITH
HOT TEMPERATURES AND HEAT INDICES RANGING FROM 108 TO 111 DEGREES.|
LONG TERM(MONDAY THROUGH FRIDAY)
ISSUED AT 258 AM AST FRI AUG 21 2026
THE MAIN LONG-TERM FORECAST CONCERNS ARE PERSISTENT EXCESSIVE HEAT
AND THE EVOLUTION OF THE MID-LEVEL RIDGE AS A COUPLE OF WEAK
TROPICAL DISTURBANCES MOVE THROUGH THE CARIBBEAN. CONFIDENCE REMAINS
MODERATE THROUGH TUESDAY, THEN DECREASES SOMEWHAT FOR THE LATTER
HALF OF THE WEEK AS MODEL DIFFERENCES BECOME MORE PRONOUNCED.
ON MONDAY, THE DETERMINISTIC GFS SUGGESTS THE MID-LEVEL RIDGE WILL
ERODE BY THE AFTERNOON. IF THIS OCCURS, REDUCED MID-LEVEL INHIBITION
COMBINED WITH DAYTIME HEATING AND LOCAL EFFECTS SHOULD SUPPORT A
BETTER OPPORTUNITY FOR AFTERNOON CONVECTION ACROSS THE INTERIOR AND
WESTERN PORTIONS OF PUERTO RICO. FARTHER EAST, THE U.S. VIRGIN
ISLANDS AND WINDWARD PORTIONS OF PUERTO RICO SHOULD EXPERIENCE
MAINLY ISOLATED, FAST-MOVING SHOWERS. LIMITED TO ELEVATED EXCESSIVE
HEAT CONDITIONS WILL REMAIN A CONCERN, PARTICULARLY ACROSS COASTAL
AND URBAN AREAS.
BY TUESDAY, A WEAK TROPICAL WAVE IS FORECAST TO APPROACH THE REGION.
HOWEVER, THE DETERMINISTIC GFS AND ECMWF DIFFER ON THE STRENGTH OF
THE MID-LEVEL RIDGE AND ASSOCIATED MOISTURE. NEVERTHELESS,
INCREASING MOISTURE SHOULD SUPPORT SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS THE U.S. VIRGIN ISLANDS AND EASTERN PUERTO RICO
AS EARLY AS TUESDAY MORNING, FOLLOWED BY ADDITIONAL CONVECTION OVER
THE INTERIOR AND WESTERN PORTIONS OF PUERTO RICO DURING THE
AFTERNOON. CONFIDENCE IN RAINFALL COVERAGE AND AMOUNTS REMAINS
LIMITED, HOWEVER. THE GFS IS MORE AGGRESSIVE IN WEAKENING THE MID-
LEVEL RIDGE, WHILE GUIDANCE ALSO SUGGESTS INCREASING TRADE WINDS. A
FASTER LOW-LEVEL FLOW COULD LIMIT RAINFALL DURATION AND REDUCE THE
POTENTIAL FOR SIGNIFICANT ACCUMULATIONS.
ANY RAINFALL WOULD BE BENEFICIAL GIVEN THE ONGOING DROUGHT
CONDITIONS ACROSS PORTIONS OF PUERTO RICO AND THE U.S. VIRGIN
ISLANDS, PARTICULARLY IF PRECIPITATION OCCURS WITHIN RESERVOIR
WATERSHEDS. HOWEVER, GIVEN THE EXPECTED PROGRESSIVE NATURE OF THE
SHOWERS AND CURRENT MODEL UNCERTAINTY, CONFIDENCE REMAINS LOW THAT
THIS WAVE WILL PROVIDE MEANINGFUL DROUGHT RELIEF.
GUIDANCE GENERALLY FAVORS THE MID-LEVEL RIDGE REBUILDING OVER THE
REGION WEDNESDAY, WHICH SHOULD ONCE AGAIN SUPPRESS WIDESPREAD
CONVECTION WHILE MAINTAINING HOT CONDITIONS. ANOTHER DISTURBANCE IS
BEING MONITORED FOR THURSDAY, ALTHOUGH CURRENT GFS GUIDANCE KEEPS
THE BULK OF ITS MOISTURE AND ASSOCIATED ACTIVITY SOUTH OF THE LOCAL
ISLANDS OVER THE CARIBBEAN SEA. ANOTHER POSSIBLE TROPICAL WAVE MAY
APPROACH FRIDAY, BUT CURRENT GUIDANCE SUGGESTS LIMITED ORGANIZATION
AND MOISTURE. GIVEN THE LEAD TIME AND MODEL VARIABILITY, CONFIDENCE
IN THE THURSDAY-FRIDAY EVOLUTION REMAINS LOW.
OVERALL, PERIODS OF EXCESSIVE HEAT WILL REMAIN ONE OF THE PRIMARY
HAZARDS DURING THE LONG-TERM PERIOD, PARTICULARLY MONDAY AND TUESDAY
AND POTENTIALLY INTO WEDNESDAY. RAINFALL OPPORTUNITIES WILL INCREASE
AT TIMES WITH PASSING DISTURBANCES, BUT CONFIDENCE IN SIGNIFICANT OR
WIDESPREAD ACCUMULATIONS REMAINS LOW.
AVIATION
(06Z TAFS)
ISSUED AT 258 AM AST FRI AUG 21 2026
MAINLY VFR CONDITIONS ARE EXPECTED ACROSS ALL TAF SITES. SAHARAN DUST
WILL CONTINUE TO PROMOTE HAZY CONDITIONS, REDUCING THE VIS ALONG
THE SITES. WINDS WILL REMAIN GENERALLY FROM THE E THROUGHOUT THE
PERIOD. WIND SPEEDS WILL INCREASE TO AROUND 15 KT AFTER 21/14Z.
SOME VCSH WILL BE POSSIBLE NEAR TJBQ DURING THE AFTERNOON. NO
SIGNIFICANT OPERATIONAL IMPACTS ARE EXPECTED AT THIS TIME.
MARINE
ISSUED AT 258 AM AST FRI AUG 21 2026
LOCALLY CHOPPY CONDITIONS WILL PREVAIL ACROSS PORTIONS OF THE
OFFSHORE WATERS AND LOCAL PASSAGES THROUGH THE END OF THE WORKWEEK,
DUE TO MODERATE AND LOCALLY FRESH EASTERLY WINDS. SMALL CRAFT SHOULD
EXERCISE CAUTION REMAIN IN EFFECT. SEAS 4 TO 5 FEET, OCCASIONALLY
TO 6 FEET ACROSS OFFSHORE WATERS WHILE 3 TO 4 ACROSS COASTAL
WATERS. WINDS WILL GRADUALLY SUBSIDE AS WE HEAD INTO THE WEEKEND,
THOUGH OCCASIONALLY BREEZY CONDITIONS MAY PERSIST ACROSS THE MORE
EXPOSED WATERS.
BEACH FORECAST
ISSUED AT 258 AM AST FRI AUG 21 2026
EXPECT MODERATE RISK OF RIP CURRENTS ALONG THE BEACHES OF NORTHERN
AND EASTERN PUERTO RICO, CULEBRA, VIEQUES, AND THE U.S. VIRGIN
ISLANDS, MEANING LIFE-THREATENING RIP CURRENTS THROUGH TONIGHT.
LOWER RISK WILL PREVAIL ELSEWHERE. HOWEVER, REMEMBER THAT EVEN WHEN
THE RISK IS LOW, LIFE-THREATENING RIP CURRENTS CAN OCCUR NEAR
GROINS, JETTIES, REEFS, AND PIERS. FROM TUESDAY INTO MIDWEEK, WINDS
ARE EXPECTED TO GRADUALLY BECOME BREEZIER, WITH A MODERATE RISK
EXPANDING TO MOST LOCAL BEACHES.
FIRE WEATHER
ISSUED AT 258 AM AST FRI AUG 21 2026
AN ELEVATED FIRE DANGER THREAT IS EXPECTED TODAY DUE TO THE
COMBINATION OF DRY ATMOSPHERIC CONDITIONS AND BREEZY WINDS.
RELATIVE HUMIDITY (RH) VALUES ARE FORECAST TO DROP INTO THE MID TO
LOWER 40S DURING THE PEAK HEATING HOURS OF THE AFTERNOON.
COMBINED WITH SUSTAINED EAST-SOUTHEAST WINDS BETWEEN 10 AND 15 MPH
AND DRY FUELS AND SOILS, ENVIRONMENTAL CONDITIONS WILL BE
FAVORABLE FOR RAPID FIRE IGNITION AND SPREAD. THEREFORE, A FIRE
DANGER STATEMENT (RFD) WILL BE ISSUED FOR THE AFFECTED AREA.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY FROM 10 AM THIS MORNING TO 5 PM AST THIS AFTERNOON
FOR PRZ001>005-007-008-010>013.
VI...HEAT ADVISORY FROM 10 AM THIS MORNING TO 5 PM AST THIS AFTERNOON
FOR VIZ001-002.
AM...NONE.
SHORT TERM, AVIATION & KEY MESSAGES...LIS
LONG TERM....CAM
MARINE & BEACH FORECAST...MMC
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