702
FXCA62 TJSJ 210637
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
237 AM AST MON SEP 21 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 215 AM AST MON SEP 21 2026
- A SEASONAL WEATHER PATTERN WILL PERSIST ACROSS PUERTO RICO AND
THE U.S. VIRGIN ISLANDS DURING THE NEXT FEW DAYS, WITH AFTERNOON
SHOWERS AND THUNDERSTORMS ACROSS CENTRAL, NORTHERN, AND WESTERN
PUERTO RICO.
- A HEAT ADVISORY IS IN EFFECT FROM 10 AM TO 3 PM AST FOR ALL
PUERTO RICO, VIEQUES, CULEBRA AND THE U.S. VIRGIN ISLANDS.
- A WETTER AND MORE UNSTABLE PATTERN WILL RETURN BY MID-WEEK,
INCREASING THE POTENTIAL FOR WIDESPREAD HEAVY RAINFALL AND
STRONGER THUNDERSTORMS.
- HOT AND HUMID CONDITIONS WILL CONTINUE THROUGHOUT THE WEEK, WITH
HEAT CONCERNS EACH DAY, PARTICULARLY BEFORE THE ONSET OF
AFTERNOON SHOWERS.
SHORT TERM(TODAY THROUGH WEDNESDAY)
ISSUED AT 215 AM AST MON SEP 21 2026
A SEASONAL WEATHER PATTERN, WITH HIGH HEAT INDICES AND CONVECTION
DURING THE AFTERNOON IS EXPECTED TODAY. A HEAT ADVISORY WILL BE
IN EFFECT FROM 10 AM TO 3 PM. LOCALS AND VISITORS ARE ENCOURAGED
TO REMAIN HYDRATED AND AVOID OUTDOOR ACTIVITIES, ESPECIALLY DURING
PEAK DAYTIME HEATING HOURS. SEASONAL TO ABOVE-SEASONAL
PRECIPITABLE WATER (PWAT) VALUES RANGING FROM 1.70 TO 2.10 INCHES
WILL SUPPORT PASSING MORNING SHOWERS DURING THE MORNING OVER THE
USVI AND EASTERN PORTIONS. LIGHT WINDS FROM A SOUTHEASTERLY FLOW
WILL PROMOTE SHOWERS AND THUNDERSTORM ACTIVITY ENHANCED BY LOCAL
EFFECTS DURING THE AFTERNOON, ESPECIALLY OVER THE NORTHWESTERN
PORTIONS OF PUERTO RICO. ON TUESDAY, A SIMILAR PATTERN IS
EXPECTED, HOWEVER, A TROUGH IN MID- TO-HIGH LEVELS SHOULD ENHANCE
INSTABILITY, WHICH COULD RESULT IN STRONGER AFTERNOON CONVECTION
OVER THE CWA. IN ADDITION, A MORE EASTERLY FLOW AND PREVAILING
LIGHT WINDS COULD ALLOW SHOWERS AND THUNDERSTORMS DEVELOPMENT OVER
MOST OF THE LOCAL AREA. MOVING INTO MID-WEEK, A WEAK MID-LEVEL
RIDGE WILL ALLOW DRIER AIR INTRUSION AND A SURFACE HIGH PRESSURE
WILL PROMOTE WINDS STRENGTHENING GRADUALLY TO SEASONAL LEVELS BY
THE END OF WORKWEEK. AS A RESULT, PWAT VALUES ARE ANTICIPATED TO
DIMINISH TO SUB-SEASONAL TO SEASONAL RANGES (1.6- 2.00 INCHES) BY
WEDNESDAY. NONETHELESS, AFTERNOON CONVECTION COULD STILL BE
POSSIBLE OVER WESTERN AND INTERIOR PORTIONS.
OVERALL, THE PRIMARY WEATHER HAZARDS WILL INCLUDE HEAT-RELATED
RISKS, LOCALIZED HEAVY RAINFALL, AND ISOLATED THUNDERSTORMS, WHICH
COULD BE ACCOMPANIED BY FREQUENT LIGHTNING AND STRONG GUSTS. TUESDAY
IS EXPECTED TO BE THE MOST UNSTABLE DAY, AS LIGHT WINDS COULD LEAD
TO SLOW-MOVING STORMS THAT HEIGHTEN THE RISK OF EXCESSIVE RAINFALL,
PARTICULARLY IN THE AFTERNOON. WHILE MONDAY AND TUESDAY FACE A
LIMITED TO ELEVATED RISK OF EXCESSIVE RAIN—PRIMARILY IMPACTING
INTERIOR, NORTHWESTERN, AND WESTERN AREAS—THIS RISK WILL DECREASE TO
A LIMITED LEVEL ON WEDNESDAY AS MID-LEVEL MOISTURE DROPS.
CONSEQUENTLY, THESE CONDITIONS MAY LEAD TO WATER PONDING ON
ROADWAYS, URBAN AND SMALL STREAM FLOODING, AND EVEN ISOLATED FLASH
FLOODS IN AREAS WITH AN ELEVATED RISK LEVEL, ALONGSIDE A CONTINUED
RISK OF LANDSLIDES WHERE TERRAIN IS ALREADY SATURATED FROM RECENT
RAINFALL.
LONG TERM(THURSDAY THROUGH MONDAY)
ISSUED AT 215 AM AST MON SEP 21 2026
SURFACE HIGH PRESSURE ACROSS THE CENTRAL TO EASTERN ATLANTIC WILL
PROMOTE MAINLY SOUTHEASTERLY LOW-LEVEL WIND FLOW DURING MOST OF THE
LONG-TERM PERIOD, BECOMING MORE EASTERLY EARLY NEXT WEEK, AT AROUND
10 TO 18 KNOTS. THE LATEST MODELS SHOW THAT PRECIPITABLE WATER
CONTENT WILL REMAIN MAINLY NEAR SEASONAL VALUES, BETWEEN 1.75 AND
2.0 INCHES, EXCEPT FROM FRIDAY NIGHT INTO EARLY SATURDAY, WHEN
VALUES MAY DECREASE TO AROUND 1.5 INCHES (25TH PERCENTILE), AS LOW
CONCENTRATIONS OF SAHARAN DUST PARTICLES ARE EXPECTED TO START
ARRIVING.
BY THURSDAY AND FRIDAY, MODELS CONTINUE TO INDICATE MID TO UPPER-
LEVEL LOWS, BRINGING SOME INSTABILITY AND 500-MB TEMPERATURES
COOLING TO BELOW-SEASONAL VALUES, AROUND -8 TO -9 DEGREES CELSIUS.
MODELS HAVE BEEN ADJUSTING, BRINGING DRIER AIR INTO THE 850 TO 700-
MB LEVELS AND ALSO INTO THE MID TO UPPER LEVELS DURING THE WEEKEND.
WITH MARGINAL INSTABILITY ALOFT, DAYTIME HEATING, AND LOCAL EFFECTS,
AT THIS TIME THURSDAY AND FRIDAY LOOK LIKE TWO DAYS WITH FREQUENT
PASSING SHOWERS ACROSS WINDWARD AREAS AND THE U.S. VIRGIN ISLANDS,
ALONG WITH STRONG AFTERNOON THUNDERSTORMS ACROSS PARTS OF THE
INTERIOR INTO NORTHWESTERN PUERTO RICO. IF THIS SCENARIO
MATERIALIZES, IT COULD PRODUCE HEAVY RAINFALL, FREQUENT LIGHTNING,
AND LOCALLY GUSTY WINDS. A LIMITED TO ELEVATED FLOODING RISK IS
POSSIBLE DURING THIS PERIOD, MEANING THAT FLOODING IN URBAN AREAS,
ON ROADS, AND IN SMALL STREAMS AND WASHES IS POSSIBLE.
AS PREVIOUSLY MENTIONED, SATURDAY LOOKS LIKE THE DAY SAHARAN DUST
WILL START TO INFILTRATE THE ISLANDS. ADDITIONAL MID-LEVEL DRYING IS
EXPECTED. AS A RESULT, RAIN CHANCES ARE EXPECTED TO DECREASE, AND
AFTERNOON SHOWERS AND ISOLATED THUNDERSTORMS, DRIVEN BY LOCAL
EFFECTS, SHOULD REMAIN MORE CONFINED TO NORTHWESTERN PUERTO RICO AND
DECREASE IN INTENSITY. FROM SUNDAY INTO EARLY NEXT WEEK, LOW-LEVEL
WINDS ARE ALSO EXPECTED TO STRENGTHEN SOMEWHAT AND AVAILABLE
MOISTURE GRADUALLY INCREASE. THAT SHOULD ALLOW FOR A MORE TYPICAL
PATTERN, WITH MORNING SHOWERS ACROSS EASTERN PUERTO RICO AND THE
U.S. VIRGIN ISLANDS, FOLLOWED BY AFTERNOON CONVECTION ACROSS WESTERN
SECTORS OF PUERTO RICO.
A PERSISTENT HAZARD DURING THE LONG TERM WILL BE THE HEAT. IT WILL
LARGELY DEPEND ON CLOUD COVER AND THE COVERAGE AND TIMING OF
SHOWERS, BUT OVERALL, THE COMBINATION OF SEASONAL MOISTURE, MAINLY
SOUTHEASTERLY WINDS, AND 925-MB TEMPERATURES AROUND TWO STANDARD
DEVIATIONS ABOVE NORMAL WILL LIKELY RESULT IN WARM TO HOT
CONDITIONS, PARTICULARLY FROM 11 AM TO 4 PM, WHICH ARE TYPICALLY THE
PEAK HEAT HOURS.
AVIATION
(06Z TAFS)
ISSUED AT 215 AM AST MON SEP 21 2026
MOSTLY VFR CONDS EXPECTED ACROSS ALL TERMINALS THRU THE FORECAST
PERIOD. PASSING SHRA MAY RESULT IN VCSH AND BRIEFLY LOWER
VIS/CIGS AT TJSJ/TIST/TISX THRU 21/14Z. SHRA/TSRA WILL INCREASE
ACROSS CENTRAL AND WESTERN PR AFT 21/16-17Z, AFFECTING MOSTLY
TJBQ/TJSJ. WINDS LIGHT/VRB OVERNIGHT, BECOMING E-ESE 10-15 KT
AFTER 21/14Z WITH SEA-BREEZE VARIATIONS AND HIGHER GUSTS NEAR
TSRA. LIGHT/VRB WINDS EXPECTED OVERNIGHT AFT 21/23Z.
MARINE
ISSUED AT 215 AM AST MON SEP 21 2026
A WEAK SURFACE HIGH PRESSURE NORTH OF THE REGION WILL MAINTAIN
GENTLE TO MODERATE EASTERLY TRADES OF 5 TO 15 KNOTS THROUGH MONDAY,
WITH WINDS GRADUALLY BECOMING EAST BY LATE MONDAY INTO MIDWEEK AS
HIGH PRESSURE OVER THE NORTHEASTERN ATLANTIC BECOMES BETTER
ORGANIZED. SEAS WILL REMAIN AROUND 2 TO 4 FEET ACROSS THE ATLANTIC
AND CARIBBEAN WATERS, INCLUDING THE LOCAL PASSAGES. PASSING SHOWERS
MAY BRIEFLY INCREASE WINDS AND SEAS, WHILE AFTERNOON THUNDERSTORMS
MOVING INTO THE WESTERN COASTAL WATERS OF PUERTO RICO MAY PRODUCE
LOCALLY STRONG GUSTS, TORRENTIAL RAINFALL, AND FREQUENT LIGHTNING
THROUGH THE EARLY EVENING HOURS.
BEACH FORECAST
ISSUED AT 215 AM AST MON SEP 21 2026
EXPECT THE LOW RIP CURRENT RISK TO PREVAIL ACROSS PUERTO RICO AND
THE U.S. VIRGIN ISLANDS THROUGH MIDWEEK. HOWEVER, EVEN WITH A LOW
RISK, LIFE-THREATENING RIP CURRENTS CAN OCCUR NEAR GROINS, JETTIES,
REEFS, AND PIERS. FROM LATE WEDNESDAY ONWARD, A MODERATE RISK IS
EXPECTED TO RETURN ACROSS THE NORTH AND EAST-FACING BEACHES OF THE
ISLANDS, DUE TO A SMALL LONG-PERIOD NORTHEASTERLY SWELL AND AS WINDS
INCREASE SLIGHTLY ACROSS THE COASTAL WATERS. OTHER BEACH HAZARDS
WILL BE HEAT, AND THUNDERSTORMS WITH GUSTY WINDS AND LIGHTNING
STRIKES DURING THE AFTERNOON HOURS. BEACHGOERS SHOULD REMAIN
HYDRATED AND LIMIT PROLONGED SUN EXPOSURE, AND SEEK SHELTER WHENEVER
THEY HEAR THUNDER.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY FROM 10 AM THIS MORNING TO 3 PM AST THIS AFTERNOON
FOR PRZ001>013.
VI...HEAT ADVISORY FROM 10 AM THIS MORNING TO 3 PM AST THIS AFTERNOON
FOR VIZ001-002.
AM...NONE.
SHORT TERM...JCP
LONG TERM....YZR
MARINE/BEACH FORECAST...MMC
AVIATION...GRS
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page