980
FXCA62 TJSJ 200844
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
444 AM AST MON JUL 20 2026
...NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER...
KEY MESSAGES
ISSUED AT 441 AM AST MON JUL 20 2026
* HAZY SKIES ASSOCIATED WITH SAHARAN DUST WILL PERSIST THROUGH PART
OF TODAY, WITH CONDITIONS GRADUALLY IMPROVING THIS AFTERNOON.
TODAY WILL ALSO BE THE DRIEST DAY OF THE FORECAST PERIOD, WITH
ONLY ISOLATED AFTERNOON SHOWERS EXPECTED OVER WESTERN PUERTO RICO.
* HEAT INDICES WILL GENERALLY REMAIN BELOW HEAT ADVISORY CRITERIA
TODAY, ALTHOUGH VALUES ABOVE 100F ARE STILL EXPECTED ACROSS SOME
COASTAL AND URBAN AREAS. THE HEAT THREAT WILL INCREASE TUESDAY AND
WEDNESDAY, WITH HEAT ADVISORIES OR EVEN EXTREME HEAT WARNINGS
BECOMING POSSIBLE ACROSS PORTIONS OF THE LOWER ELEVATIONS.
* A TRANSITION TO A MORE UNSETTLED WEATHER PATTERN IS EXPECTED
TUESDAY THROUGH WEDNESDAY AS MOISTURE INCREASES ACROSS THE
REGION AND A TROUGH MOVES ACROSS THE AREA. SHOWERS AND ISOLATED
THUNDERSTORMS WILL BECOME MORE LIKELY EACH AFTERNOON, ESPECIALLY
ACROSS WESTERN PUERTO RICO, WITH A LIMITED RISK OF LOCALIZED
URBAN AND SMALL-STREAM FLOODING.
* ELEVATED FIRE WEATHER CONDITIONS WILL PERSIST TODAY, WHERE
CRITICALLY DRY VEGETATION, LOW RELATIVE HUMIDITY, AND BREEZY
CONDITIONS WILL CONTINUE TO SUPPORT THE RAPID SPREAD OF FIRES.
SHORT TERM(TODAY THROUGH WEDNESDAY)
ISSUED AT 441 AM AST MON JUL 20 2026
OVERNIGHT CONDITIONS WERE GENERALLY TRANQUIL ACROSS PUERTO RICO AND
THE U.S. VIRGIN ISLANDS. A FEW PASSING SHOWERS ASSOCIATED WITH A
WEAK TROPICAL WAVE MOVING WESTWARD WERE OBSERVED OVER THE CARIBBEAN
WATERS, BUT NO MEASURABLE PRECIPITATION WAS DETECTED OVER LAND. THE
FORECAST AREA REMAINS EMBEDDED WITHIN A PLUME OF MODERATE SAHARAN
DUST, RESULTING IN HAZY SKIES AND REDUCED MOISTURE. HOWEVER, GEOS-5
GUIDANCE INDICATES IMPROVING CONDITIONS THIS AFTERNOON AS THE DUST
PLUME IS PUSHED SOUTHWARD BY AN APPROACHING SURFACE INVERTED TROUGH
INDUCED BY A TUTT LOW TO THE NORTHEAST.
IN THE WAKE OF THE DUST PLUME, A PRONOUNCED DRY SLOT IS EXPECTED TO
OVERSPREAD THE REGION, WITH PRECIPITABLE WATER VALUES FALLING TO
NEAR 1.0 INCH, WELL BELOW CLIMATOLOGICAL NORMALS AND BELOW TWO
STANDARD DEVIATIONS FOR THIS TIME OF YEAR. COMBINED WITH PERSISTENT
MID-LEVEL RIDGING, WARM TEMPERATURES ALOFT, AND RELATIVELY DRY MID-
LEVELS, THIS WILL SUPPORT THE DRIEST AND MOST STABLE CONDITIONS OF
THE FORECAST PERIOD TODAY, LIMITING SHOWER DEVELOPMENT TO ISOLATED
AFTERNOON CONVECTION OVER PORTIONS OF THE WESTERN INTERIOR. THE
APPROACHING TROUGH WILL ALSO WEAKEN THE LOCAL PRESSURE GRADIENT,
RESULTING IN SLIGHTLY LIGHTER EASTERLY WINDS COMPARED TO RECENT
DAYS. WHILE TEMPERATURES WILL REMAIN NEAR SEASONAL NORMALS, THE
DRIER AIR MASS MAY PROVIDE SOME RELIEF FROM HEAT STRESS, ALTHOUGH
HEAT INDICES WILL STILL APPROACH ABOVE 100S F ACROSS SOME COASTAL
AND URBAN AREAS.
A TRANSITION TOWARD A MORE UNSETTLED WEATHER PATTERN IS EXPECTED ON
TUESDAY AS A SURFACE INVERTED TROUGH AND AN ACCOMPANYING TROPICAL
UPPER-TROPOSPHERIC TROUGH (TUTT) LOW MOVE ACROSS THE NORTHEASTERN
CARIBBEAN FROM THE EAST-NORTHEAST. AS THE RIDGE WEAKENS, DEEP-LAYER
MOISTURE WILL RECOVER TO NEAR OR SLIGHTLY ABOVE NORMAL, WHILE
INSTABILITY ALOFT GRADUALLY INCREASES. THIS WILL FAVOR MORE
WIDESPREAD SHOWER ACTIVITY AND ISOLATED THUNDERSTORMS, PARTICULARLY
DURING THE AFTERNOON ACROSS WESTERN AND SOUTHWESTERN PUERTO RICO
UNDER AN EAST-NORTHEASTERLY WIND FLOW. SIMILAR CONDITIONS ARE
ANTICIPATED ON WEDNESDAY; HOWEVER, LOW-LEVEL WINDS ARE FORECAST TO
VEER TO THE EAST-SOUTHEAST BEHIND THE TROUGH AXIS. THIS SHIFT SHOULD
FOCUS AFTERNOON CONVECTION ACROSS WESTERN AND NORTHWESTERN PUERTO
RICO WHILE ALSO PROMOTING WARMER TEMPERATURES ACROSS THE ISLANDS.
CONSEQUENTLY, THE HEAT THREAT IS EXPECTED TO INCREASE, WITH HEAT
ADVISORY OR EVEN EXTREME HEAT WARNING CONDITIONS BECOMING POSSIBLE
ACROSS COASTAL AND URBAN AREAS UNDER THE DEVELOPING SOUTHEASTERLY
FLOW AND INCREASING MOISTURE.
OVERALL, LIMITED IMPACTS ARE EXPECTED TODAY AS THE COMBINATION OF
ANOMALOUSLY DRY AIR AND PERSISTENT MID-LEVEL RIDGING SUPPRESSES
WIDESPREAD CONVECTION. HAZY SKIES ASSOCIATED WITH LINGERING SAHARAN
DUST WILL PERSIST THROUGH AT LEAST PART OF THE DAY BEFORE GRADUALLY
IMPROVING THIS AFTERNOON. ISOLATED AFTERNOON SHOWERS OVER THE
WESTERN INTERIOR MAY STILL PRODUCE BRIEF PERIODS OF LOCALLY HEAVY
RAINFALL. BEGINNING TUESDAY AND CONTINUING INTO WEDNESDAY,
INCREASING MOISTURE AND INSTABILITY WILL SUPPORT A GREATER COVERAGE
OF SHOWERS AND THUNDERSTORMS, RAISING THE POTENTIAL FOR LOCALIZED
URBAN AND SMALL-STREAM FLOODING, PARTICULARLY WHERE SHOWERS
REPEATEDLY DEVELOP OVER INTERIOR AND WESTERN PUERTO RICO. IN
ADDITION, THE HEAT THREAT IS EXPECTED TO INCREASE UNDER A DEVELOPING
EAST-SOUTHEASTERLY WIND FLOW AND HIGHER MOISTURE CONTENT,
POTENTIALLY RESULTING IN DANGEROUS HEAT INDICES ACROSS COASTAL AND
URBAN AREAS, ESPECIALLY BY WEDNESDAY.
LONG TERM(THURSDAY THROUGH MONDAY)
ISSUED AT 441 AM AST MON JUL 20 2026
FOR THE SECOND HALF OF THE WORKWEEK, UPPER LEVEL LOWS WILL CONTINUE
TO LINGER NORTHEAST AND THEN EAST-SOUTHEAST OF THE REGION. A SURFACE
HIGH OVER THE ATLANTIC WILL REESTABLISH ITSELF AND ONCE AGAIN RESULT
IN UP TO BREEZY CONDITIONS, ESPECIALLY FRIDAY AND SATURDAY. CURRENT
MODEL GUIDANCE HAS PRECIPITABLE WATER (PWAT) VALUES ON A DOWNWARD
TREND TO START THE LONG TERM PERIOD AS MOISTURE FROM A SURFACE
TROUGH MOVES NORTHEAST AND AWAY FROM THE REGION UNDER AN EAST-
SOUTHEAST STEERING FLOW. PWAT VALUES SHOULD STAY WITHIN NORMAL
VALUES ON THURSDAY, WITH LOCALLY ABOVE NORMAL VALUES BEING OBSERVED
DURING AFTERNOON CONVECTION OVER MAINLY W-NW PR. A DRIER AIR MASS
WITH BELOW NORMAL PWAT WILL THEN QUICKLY MOVE THURSDAY NIGHT INTO
EARLY FRIDAY, BEFORE ANOTHER PULSE OF MOISTURE REACHES THE AREA
FRIDAY MORNING. MORE HUMID AIR MASSES WILL THEN MOVE OVER THE AREA
THROUGH THE WEEKEND AS WAVES CONTINUE MOVING CLOSE TO THE REGION,
THIS WILL MAINTAIN A GENERALLY NORMAL PWAT OVER THE ISLANDS AS
SHOWERS CONTINUE TO BE STEERED TOWARDS WINDWARD SECTORS AND
AFTERNOON CONVECTION (SHOWERS AND POSSIBLE T-STORMS) DEVELOP OVER
MAINLY THE WESTERN HALF OF PUERTO RICO. AT 500 MB, TEMPERATURES ARE
FORECAST TO COOL FROM ABOVE-NORMAL VALUES TO NEAR-SEASONAL LEVELS,
AROUND -6C TO -7C, LATE THURSDAY ONWARDS. MOST AVAILABLE MOISTURE
SHOULD REMAIN BELOW 800MB THROUGH AT LEAST SATURDAY WHILE 250 MB
HEIGHTS REMAIN AT SEASONAL VALUES.
BY LATE SUNDAY THROUGH MONDAY, CURRENT GUIDANCE SUGGESTS THAT A
TROPICAL WAVE AND WIND SURGE WILL REACH THE AREA AND ELEVATE PWAT
VALUES TO ABOVE NORMAL VALUES AND RESULT IN BREEZY TO LOCALLY
WINDY E-SE FLOW. THIS WILL INCREASE THE FLOODING RISK AS QUICK
MOVING PASSING SHOWERS REACH THE REGION AND AFTERNOON CONVECTION
DEVELOPS OVER MAINLY W-PR AND DOWNWIND OF EL YUNQUE AND THE LOCAL
ISLANDS. AS AN UPPER TROUGH MOVES OVER THE REGION, AVAILABLE
MOISTURE WILL ALSO REACH THE UPPER LEVELS. WARM TO HOT CONDITIONS
WILL PERSIST THROUGH AT LEAST THE WEEKEND, WITH AN ELEVATED HEAT
RISK FORECAST FOR COASTAL AND LOWER ELEVATIONS OF THE ISLANDS. IN
TERMS OF SAHARAN DUST, LOW TO MODERATE CONCENTRATIONS WILL
CONTINUE TO FILTER OVER THE ISLANDS THROUGH THE SECOND HALF OF THE
WEEK AND EARLY NEXT WEEK, WITH GUIDANCE SUGGESTING LOWER
CONCENTRATIONS AS THE ABOVE MENTIONED MOISTURE REACHES THE ISLANDS
LATE SUNDAY AND MONDAY. CONTINUE TO MONITOR THE FORECAST FOR
UPDATES.
AVIATION
(06Z TAFS)
ISSUED AT 441 AM AST MON JUL 20 2026
VFR CONDS WILL PREVAIL AT ALL TAF SITES THRU THE FCST PD. HZ ASSOCD
WITH SAL WILL CONT TO REDUCE VIS TO AROUND 6 SM AT TIMES THIS MRNG,
WITH GRADUAL IMPROVEMENT EXPECTED THIS AFTN. ENE WINDS WILL INCR TO
15-20 KT WITH GUSTS UP TO 25 KT AFT 20/13Z, BCMG LGT/VRB AFT 19/23Z.
VCSH PSBL AFT 20/18Z-23Z AT TJBQ DUE TO DIURNAL CONVECTION. NO SIG
OPERATIONAL IMPACTS EXPECTED.
MARINE
ISSUED AT 441 AM AST MON JUL 20 2026
A SURFACE HIGH PRESSURE OVER THE CENTRAL ATLANTIC INTERACTING WITH
THE PANAMA COLOMBIA LOW WILL MAINTAIN MODERATE TO FRESH EASTERLY
WINDS AND MODERATE TO LOCALLY CHOPPY SEAS TODAY. WINDS AND SEAS WILL
GRADUALLY SUBSIDE TUESDAY INTO WEDNESDAY BEFORE WINDS INCREASE
SOMEWHAT AGAIN LATE WEDNESDAY INTO THURSDAY. SAHARAN DUST WILL
CONTINUE TO PROMOTE HAZY SKIES EARLY TODAY, WITH CONDITIONS
GRADUALLY IMPROVING THROUGH THE DAY. INCREASING MOISTURE TUESDAY
INTO WEDNESDAY WILL FAVOR MORE FREQUENT SHOWERS ACROSS THE REGION,
WITH AFTERNOON THUNDERSTORMS POSSIBLE, PARTICULARLY OVER WESTERN
PUERTO RICO.
BEACH FORECAST
ISSUED AT 441 AM AST MON JUL 20 2026
LIFE-THREATENING RIP CURRENTS ARE POSSIBLE TODAY, PARTICULARLY ALONG
NORTH-, EAST-, AND SOUTH-FACING BEACHES. RIP CURRENT CONDITIONS
IMPROVE TUESDAY AND WEDNESDAY BEFORE A MODERATE RISK RETURNS LATER
IN THE WEEK. SHOWERS AND THUNDERSTORMS INCREASE TUESDAY, WITH
CHANGING WEATHER POSSIBLE EACH AFTERNOON, ESPECIALLY ACROSS WESTERN
PUERTO RICO, WHILE EXCESSIVE HEAT BECOMES A GREATER CONCERN THROUGH
MIDWEEK. BEACHGOERS SHOULD REMAIN WEATHER-AWARE AND CHECK THE LATEST
SURF ZONE FORECAST (SRF) FOR SPECIFIC BEACH CONDITIONS BEFORE
HEADING OUT.
FIRE WEATHER
ISSUED AT 441 AM AST MON JUL 20 2026
A FIRE DANGER STATEMENT (RFD) IS IN EFFECT FOR THE LOCAL AREA.
DESPITE A SLIGHT DECREASE IN WINDS TODAY, ELEVATED FIRE WEATHER
CONDITIONS WILL PERSIST DUE TO CRITICALLY DRY FUELS, VERY LOW
RELATIVE HUMIDITY, AND PROLONGED RAINFALL DEFICITS. SEVEN-DAY
PERCENT OF NORMAL RAINFALL REMAINS BELOW 25 PERCENT ACROSS MOST OF
PUERTO RICO, WITH SOME AREAS BELOW 5-10 PERCENT, PARTICULARLY ACROSS
THE SOUTHERN COASTAL PLAINS OF PUERTO RICO. ANY FIRES THAT DEVELOP
COULD SPREAD RAPIDLY THROUGH DRY VEGETATION, ESPECIALLY ACROSS
SOUTHERN PUERTO RICO.
FIRE WEATHER CONDITIONS WILL CONTINUE TO BE MONITORED CLOSELY, AND A
RED FLAG WARNING MAY BE REQUIRED IF CONDITIONS BECOME MORE FAVORABLE
FOR RAPID FIRE GROWTH. RESIDENTS AND VISITORS ARE URGED TO AVOID
OUTDOOR BURNING AND EXERCISE EXTREME CAUTION WITH OPEN FLAMES,
DISCARDED CIGARETTES, OR ANY ACTIVITY CAPABLE OF PRODUCING SPARKS.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM, AVIATION, FIRE...CVB
LONG TERM....MRR
MARINE & BEACH FORECAST...ICP
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