103
FXCA62 TJSJ 190856
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
456 AM AST SUN JUL 19 2026
..NEW SHORT TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER
KEY MESSAGES
ISSUED AT 452 AM AST SUN JUL 19 2026
* HOT CONDITIONS WILL CONTINUE THROUGH EARLY THIS WEEK. HEAT INDICES
WILL GENERALLY REMAIN BELOW HEAT ADVISORY CRITERIA TODAY, ALTHOUGH
A FEW URBAN AND COASTAL LOCATIONS COULD BRIEFLY REACH ADVISORY
THRESHOLDS THIS AFTERNOON. THE HEAT THREAT IS EXPECTED TO INCREASE
ON MONDAY AND TUESDAY, AND HEAT ADVISORIES MAY BE NEEDED ACROSS
PORTIONS OF THE LOWER ELEVATIONS.
* A WEAK TROPICAL WAVE PASSING MAINLY SOUTH OF THE ISLANDS THIS
EVENING WILL BRING A SLIGHT INCREASE IN PASSING SHOWERS, BUT
WIDESPREAD RAINFALL IS NOT EXPECTED. MOISTURE WILL INCREASE
FURTHER ON TUESDAY AS A TROUGH APPROACHES, RESULTING IN MORE
NUMEROUS SHOWERS, ISOLATED THUNDERSTORMS, AND A LIMITED RISK OF
LOCALIZED URBAN AND SMALL-STREAM FLOODING.
* LOW TO MODERATE CONCENTRATIONS OF SAHARAN DUST WILL OVERSPREAD THE
ISLANDS TODAY THROUGH MONDAY, RESULTING IN HAZY SKIES, REDUCED AIR
QUALITY, AND LOCALLY REDUCED VISIBILITY.
* ELEVATED FIRE WEATHER CONDITIONS WILL PERSIST TODAY ACROSS
PORTIONS OF PUERTO RICO, WHERE CRITICALLY DRY VEGETATION, LOW
RELATIVE HUMIDITY, AND BREEZY CONDITIONS WILL CONTINUE TO
SUPPORT RAPID FIRE SPREAD.
SHORT TERM(TODAY THROUGH TUESDAY)
ISSUED AT 452 AM AST SUN JUL 19 2026
A FEW PASSING SHOWERS MOVED ACROSS THE LOCAL WATERS AND WINDWARD
SECTIONS DURING THE OVERNIGHT HOURS, BUT RAINFALL ACCUMULATIONS
REMAINED LIGHT. TEMPERATURES STAYED SEASONABLY WARM OVERNIGHT.
A MID-LEVEL RIDGE WILL REMAIN THE DOMINANT WEATHER FEATURE TODAY AND
MONDAY, MAINTAINING RELATIVELY WARM TEMPERATURES ALOFT AND BELOW-
NORMAL MOISTURE BETWEEN 700 AND 500 MB. MODEL GUIDANCE CONTINUES TO
INDICATE PRECIPITABLE WATER VALUES GENERALLY BETWEEN 1.2 AND 1.4
INCHES THROUGH TONIGHT AS A WEAK TROPICAL WAVE PASSES MAINLY SOUTH
OF THE LOCAL ISLANDS. ALTHOUGH THE WAVE WILL BRING A MODEST INCREASE
IN LOW-LEVEL MOISTURE, IT IS EMBEDDED WITHIN AN INCREASING SAHARAN
AIR LAYER (SAL), LIMITING VERTICAL MOISTURE DEPTH AND RESULTING IN
LITTLE OVERALL CHANGE TO THE PREVAILING WEATHER PATTERN.
CONSEQUENTLY, PASSING TRADE WIND SHOWERS WILL CONTINUE TO AFFECT THE
WINDWARD SECTORS FROM TIME TO TIME, WHILE AFTERNOON CONVECTION
REMAINS CONFINED TO PORTIONS OF WESTERN PUERTO RICO, WHERE ACTIVITY
SHOULD BE BRIEF AND LOCALIZED DUE TO PERSISTENT MID-LEVEL DRY AIR
AND SUBSIDENCE.
SAHARAN DUST CONCENTRATIONS ARE EXPECTED TO INCREASE TODAY, PEAKING
ON MONDAY, LEADING TO HAZY SKIES, REDUCED VISIBILITIES AT TIMES, AND
DETERIORATING AIR QUALITY, ESPECIALLY FOR SENSITIVE GROUPS. THE
ASSOCIATED DRY AIR MASS WILL CONTINUE TO SUPPRESS WIDESPREAD
CONVECTION DESPITE THE MODEST INCREASE IN LOW-LEVEL MOISTURE.
BY TUESDAY, A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) LOW IS
FORECAST TO SINK SOUTHWARD INTO THE NORTHEASTERN CARIBBEAN WHILE ITS
ASSOCIATED SURFACE-INDUCED INVERTED TROUGH CROSSES THE LOCAL AREA.
THIS PATTERN WILL PROMOTE A DEEPER MOISTURE PROFILE, WITH
PRECIPITABLE WATER INCREASING TO AROUND SEASONAL VALUES, ALONG WITH
HIGHER MID-LEVEL HUMIDITY AND SLIGHTLY COOLER TEMPERATURES ALOFT. AS
A RESULT, SHOWER COVERAGE IS EXPECTED TO INCREASE ACROSS THE
ISLANDS, WITH SCATTERED AFTERNOON SHOWERS AND ISOLATED THUNDERSTORMS
DEVELOPING, MOSTLY ACROSS WESTERN PUERTO RICO. LOCALLY HEAVY
RAINFALL MAY RESULT IN PONDING OF WATER ON ROADS AND LOCALIZED URBAN
AND SMALL-STREAM FLOODING, PARTICULARLY WHERE SHOWERS REPEATEDLY
AFFECT THE SAME AREAS.
HIGH TEMPERATURES WILL ONCE AGAIN CLIMB INTO THE UPPER 80S TO LOW
90S ACROSS THE URBAN AND COASTAL AREAS TODAY. HOWEVER, A SLIGHTLY
MORE EAST-NORTHEASTERLY WIND COMPONENT SHOULD PROVIDE MODEST RELIEF
COMPARED TO RECENT DAYS, WITH HEAT INDICES GENERALLY REMAINING BELOW
HEAT ADVISORY CRITERIA. NEVERTHELESS, A FEW LOCALIZED URBAN AND
COASTAL AREAS COULD BRIEFLY REACH HEAT ADVISORY THRESHOLDS DURING
THE PEAK AFTERNOON HOURS. WHILE THE OVERALL HEAT THREAT IS EXPECTED
TO REMAIN LIMITED TODAY, RESIDENTS AND VISITORS SHOULD CONTINUE TO
TAKE PRECAUTIONS TO AVOID HEAT-RELATED ILLNESSES, ESPECIALLY THOSE
SPENDING EXTENDED PERIODS OUTDOORS. BY MONDAY, THE COMBINATION OF
WARMER OVERNIGHT TEMPERATURES ASSOCIATED WITH THE SAHARAN AIR LAYER
AND PERSISTENT HAZY CONDITIONS MAY LEAD TO ELEVATED DAYTIME HEAT
INDICES, AND HEAT ADVISORIES MAY BECOME NECESSARY FOR PORTIONS OF
THE URBAN AND COASTAL AREAS. ON TUESDAY, INCREASING LOW-LEVEL
MOISTURE COMBINED WITH CONTINUED WARM TEMPERATURES MAY FURTHER
ENHANCE THE HEAT THREAT ACROSS LOWER ELEVATIONS, POTENTIALLY
REQUIRING ADDITIONAL HEAT ADVISORIES DESPITE THE EXPECTED INCREASE
IN SHOWER AND THUNDERSTORM ACTIVITY LATER IN THE DAY.
LONG TERM(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 452 AM AST SUN JUL 19 2026
DURING THE BEGINNING OF THE LONG-TERM PERIOD, THE PRIMARY WEATHER
FEATURE WILL CONTINUE TO BE AN UPPER-LEVEL LOW INDUCING A SURFACE
TROUGH NORTHEAST OF THE REGION. THIS PATTERN WILL WEAKEN THE
ATLANTIC HIGH PRESSURE SYSTEM, PROMOTING LIGHTER WINDS ACROSS THE
ISLANDS. THE LATEST GUIDANCE SUGGESTS THAT ENVIRONMENTAL CONDITIONS
WILL BE MARGINALLY FAVORABLE FOR CONVECTIVE ACTIVITY. WINDS WILL
BECOME LIGHTER FROM THE EAST-NORTHEAST. AT 500 MB, TEMPERATURES ARE
FORECAST TO COOL FROM ABOVE-NORMAL VALUES TO NEAR-SEASONAL LEVELS,
AROUND -6C TO -7C. IN ADDITION, LOWER 250 MB HEIGHTS, NEAR-
SEASONAL MID-LEVEL RELATIVE HUMIDITY, AND PRECIPITABLE WATER
(PWAT) VALUES REMAINING AROUND 1.7 TO 1.9 INCHES WILL SUPPORT A
MORE FAVORABLE ENVIRONMENT FOR SHOWER AND THUNDERSTORM
DEVELOPMENT. A LIMITED FLOOD RISK IS HIGHLIGHTED ACROSS WEST-
CENTRAL AND WESTERN PUERTO RICO DUE TO THE POTENTIAL FOR PONDING
OF WATER ON ROADS AND IN POORLY DRAINED AREAS, ALONG WITH A LOW
CHANCE OF URBAN AND SMALL- STREAM FLOODING.
ADDITIONALLY, ON WEDNESDAY, THE COMBINATION OF LIGHT SOUTHEASTERLY
FLOW, SEASONAL MOISTURE, AND 925 MB TEMPERATURES AROUND TWO STANDARD
DEVIATIONS ABOVE NORMAL IS EXPECTED TO RESULT IN THE WARMEST DAY OF
THE WEEK. HEAT INDEX VALUES WILL LIKELY REACH HAZARDOUS LEVELS EACH
AFTERNOON, ESPECIALLY ACROSS URBAN AND COASTAL LOCATIONS. A
SIGNIFICANT HEAT RISK IS CURRENTLY HIGHLIGHTED FOR WEDNESDAY. HEAT
PRODUCTS WILL LIKELY NEED TO BE ISSUED.
BY THURSDAY AND THROUGH THE REMAINDER OF THE FORECAST PERIOD,
SLIGHTLY DRIER AIR IS EXPECTED TO FILTER INTO THE REGION, WITH PWAT
VALUES FLUCTUATING BETWEEN SEASONAL AND BELOW-NORMAL LEVELS,
RESULTING IN MORE LIMITED SHOWER ACTIVITY. WINDS ARE FORECAST TO
STRENGTHEN ONCE AGAIN, BECOMING BREEZY TO LOCALLY WINDY THROUGH THE
WEEKEND. THE EASTERLY STEERING FLOW WILL CONTINUE TO FAVOR PASSING
SHOWERS ACROSS WINDWARD AREAS DURING THE NIGHTTIME AND MORNING
HOURS, FOLLOWED BY AFTERNOON SHOWERS OVER WESTERN PUERTO RICO DRIVEN
BY LOCAL EFFECTS AND AVAILABLE MOISTURE. THE FLOOD RISK IS EXPECTED
TO REMAIN LOW, ALTHOUGH A FEW ISOLATED THUNDERSTORMS WILL REMAIN
POSSIBLE EACH AFTERNOON ACROSS WESTERN PUERTO RICO. IN TERMS OF
HEAT, WARM TO HOT CONDITIONS ARE LIKELY TO PERSIST MOST DAYS. AN
ELEVATED HEAT RISK IS CURRENTLY IN PLACE FOR THURSDAY, WHILE A
LIMITED HEAT RISK IS EXPECTED ON FRIDAY. CONTINUE TO MONITOR THE
FORECAST FOR UPDATES. RESIDENTS AND VISITORS ARE ENCOURAGED TO
CONTINUE PRACTICING HEAT SAFETY MEASURES TO REDUCE THE RISK OF HEAT-
RELATED ILLNESSES.
AVIATION
(06Z TAFS)
ISSUED AT 452 AM AST SUN JUL 19 2026
VFR CONDS WILL PREVAIL AT ALL TAF SITES THRU THE FCST PD. ENE WINDS
8-12 KT WILL INCREASE TO 15-20 KT WITH GUSTS UP TO 25-30 KT AFT
19/13Z, BCMG LIGHTER (8-12 KT) AFT 19/23Z. VCSH PSBL AT TIMES,
WITH BRIEF SHRA MAINLY AFFECTING ERN TERMINALS DURING THE MRNG AND
WRN PR DURING THE AFTN. HZ ASSOCIATED WITH SAL MAY REDUCE VSBY TO
6 SM AT TIST/TISX AFT 19/22Z. NO SIG OPERATIONAL IMPACTS
EXPECTED.
MARINE
ISSUED AT 452 AM AST SUN JUL 19 2026
A SURFACE HIGH PRESSURE OVER THE CENTRAL ATLANTIC INTERACTING WITH
THE PANAMA–COLOMBIA LOW WILL MAINTAIN MODERATE TO LOCALLY FRESH
EASTERLY WINDS AND MODERATE TO LOCALLY CHOPPY SEAS THROUGH MUCH OF
THE FORECAST PERIOD. SMALL CRAFT SHOULD EXERCISE CAUTION ACROSS MOST
OF THE LOCAL WATERS TODAY AND TONIGHT. A TROPICAL WAVE WILL REMAIN
WELL SOUTH OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS AS IT MOVES
WESTWARD ACROSS THE SOUTHERN CARIBBEAN FROM LATE TONIGHT INTO
TOMORROW, MONDAY. MEANWHILE, A DENSE SAHARAN AIR LAYER WILL MOVE
OVER THE REGION FROM THE EAST TONIGHT THROUGH TOMORROW, MONDAY,
LEADING TO HAZY SKIES, REDUCED AIR QUALITY, AND LOCALLY REDUCED
VISIBILITIES.
BEACH FORECAST
ISSUED AT 452 AM AST SUN JUL 19 2026
BREEZY TO LOCALLY WINDY CONDITIONS WILL PROMOTE A MODERATE RISK OF
RIP CURRENTS (RIP CURRENTS ARE POSSIBLE IN THE SURF ZONE) AT MOST OF
THE LOCAL COASTLINE/SURF ZONES. THIS MODERATE RISK IS FORECAST TO
PERSIST THROUGH AT LEAST TOMORROW, MONDAY, AND THEN RETURN BY
THURSDAY. GENERALLY WEAKER WINDS WILL RESULT IN A LOW RISK OF RIP
CURRENTS ON TUESDAY AND WEDNESDAY. HOWEVER, EVEN IF THE RISK OF RIP
CURRENTS IS LOW, LIFE-THREATENING RIP CURRENTS OFTEN OCCUR IN THE
VICINITY OF GROINS, JETTIES, REEFS, AND PIERS. BEACHGOERS SHOULD
SWIM NEAR LIFEGUARDS WHENEVER POSSIBLE, HEED BEACH WARNING FLAGS,
AND NEVER SWIM ALONE.
A LIMITED TO ELEVATED RISK OF EXCESSIVE HEAT IS ALSO EXPECTED AT
MANY LOCAL BEACHES THIS WEEK, POSSIBLY REACHING SIGNIFICANT LEVELS
ON WEDNESDAY. STAY WELL HYDRATED, SEEK SHADE WHENEVER POSSIBLE, AND
USE SUNSCREEN TO REDUCE THE RISK OF HEAT-RELATED ILLNESS. SAHARAN
DUST CONCENTRATIONS ARE FORECAST TO INCREASE TONIGHT INTO TOMORROW,
MONDAY.
FIRE WEATHER
ISSUED AT 452 AM AST SUN JUL 19 2026
A FIRE DANGER STATEMENT (RFD) IS IN EFFECT FOR THE LOCAL FIRE
WEATHER ZONES. CRITICALLY DRY FUELS AND SIGNIFICANT SOIL MOISTURE
DEFICITS PERSIST ACROSS PORTIONS OF SOUTHERN PUERTO RICO, WITH KBDI
VALUES REMAINING ABOVE CRITICAL THRESHOLDS. ALTHOUGH A WEAK TROPICAL
WAVE APPROACHING FROM THE EAST WILL RESULT IN A SLIGHT INCREASE IN
LOW-LEVEL MOISTURE LATER TODAY, THE DEEPEST MOISTURE IS EXPECTED TO
REMAIN WELL SOUTH OF THE LOCAL ISLANDS, WITH LITTLE IMPACT ON FIRE
WEATHER CONDITIONS THROUGH MOST OF THE DAY.
RELATIVE HUMIDITY VALUES ARE STILL FORECAST TO FALL INTO THE UPPER
40S TO LOWER 50S THIS AFTERNOON ACROSS THE SOUTHERN COASTAL PLAINS
OF PUERTO RICO AND ADJACENT LOWER ELEVATIONS, WHILE EASTERLY TO EAST-
NORTHEASTERLY WINDS OF 15 TO 20 MPH WITH HIGHER GUSTS WILL CONTINUE
TO SUPPORT ELEVATED FIRE WEATHER CONDITIONS. ANY RAINFALL ASSOCIATED
WITH THE TROPICAL WAVE IS EXPECTED TO BE LIGHT AND LOCALIZED,
PROVIDING LITTLE TO NO MEANINGFUL RELIEF TO THE ONGOING DRY
CONDITIONS. RESIDENTS AND VISITORS SHOULD AVOID OUTDOOR BURNING AND
EXERCISE CAUTION WHEN USING OPEN FLAMES OR OTHER POTENTIAL IGNITION
SOURCES.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM, AVIATION, FIRE...CVB
LONG TERM....YZR
MARINE & BEACH FORECAST...MRR
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