textproduct: San Juan

KEY MESSAGES

Issued at 428 AM AST Tue Sep 22 2026

- A seasonal weather pattern is expected for the next couple of days across Puerto Rico and U.S. Virgin Islands, with afternoon convection mainly over interior, western and eastern Puerto Rico.

- Heat-related risks will continue each day, Wednesday being of the greatest concern. Heat-sensitive individuals should avoid outdoor activities and stay hydrated.

- A wetter pattern is expected from Thursday as a tropical wave approach the islands, increasing the chance of stronger shower and thunderstorm activity, especially in the afternoons.

- A low rip current risk will persist today; however, gentle to moderate winds will elevate the risk to moderate by Wednesday.

Short Term(Today through Thursday)

Issued at 428 AM AST Tue Sep 22 2026

A seasonal weather pattern is expected today. Precipitable water (PWAT) values ranging from seasonal to above-seasonal ranges will allow morning showers to filter in during the morning over the USVI and eastern interior portions. Light winds from an east- southeasterly flow will promote shower and thunderstorm activity during the afternoon, especially over the northwestern portions of Puerto Rico. A couple of mid-to-upper-level lows approaching from the northeast will promote seasonal 500-mb temperatures and instability, which could result in stronger afternoon convection over the CWA. This, combined with local effects and prevailing light winds could allow shower and thunderstorm development over most of the local area.

Moving into mid-week, a drier air will filter into the mid- levels. Nonetheless, the aforementioned mid-to-upper-level lows will linger in our vicinity for the rest of the short-term period, which will continue to promote 500-mb temperatures around seasonal values, even dropping below seasonal values by Thursday. The drier air intrusion into the mid-levels should marginally limit deep convection on Wednesday, however, low-level moisture and local effects should still support afternoon convection mainly over northwestern portions. By Thursday, moisture associated to a tropical wave will reach the islands, increasing the potential for deeper convection over eastern and western to northwestern portions.

Overall, the primary weather hazards will include localized heavy rainfall, and isolated thunderstorms, which could be accompanied by frequent lightning and strong gusts. Light winds from an ESE flow on Tuesday could lead to slow-moving storms that increase the risk of excessive rainfall, particularly in the afternoon. A limited to elevated risk of excessive rainfall is expected on Tuesday, with more localized risks on Wednesday due to the drying in the mid- levels, and return to limited to elevated levels on Thursday as conditions become more favorable for stronger convection. 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.

An elevated excessive heat risk is likely on Wednesday as cloud cover is anticipated to be less than on Tuesday and Thursday, for which a limited level is expected.

Long Term(Friday through Tuesday)

Issued at 428 AM AST Tue Sep 22 2026

The main synoptic features during the long term period are a couple of multi level low pressure systems across the eastern Atlantic Ocean that will promote an east-to-southeast wind flow across the CWA. Winds are expected to bring calm-to-breezy conditions throughout the region potentially favoring the ocasional development of streamers from the US Virgin Islands, Vieques, Culebra and El Yunque rainforest. Low-to-moderate concentrations of Saharan Dust will filter by Friday onwards bringing PWAT values down to 1.2 inches during the weekend. Sensitive groups should remain alert as air quality may deteriorate. PWAT values will return to seasonal levels by Monday. The potential for rain each day is expected to be focused on the northwestern side of Puerto Rico and will be driven by local effects such as sea-breeze convergence, orographic effects and diurnal heating.Besides the flooding risk, visitors and citizens should experience periods of excessive heat threats. With humidity values ranging around seasonal levels and 925mb temperatures being 2 standard deviations above the normal values, the extreme heat risk remains elevated thruough Sunday across coastal, urban, and exposed areas, with conditions expected to vary with cloud coverage. This level of heat affects anyone without effective cooling and/or adequate hydration. With impacts likely in some health systems, heat sensitive industries and infrastructure. It is recommended that individuals limit outdoor activities and remain hydrated. It is recommended that individuals follow the instructions of health officials and monitor the evolving weather conditions.

AVIATION

(06Z TAFS) Issued at 428 AM AST Tue Sep 22 2026

Mostly VFR. SHRA/TSRA increase aftn, mainly TJSJ/TJBQ, with VCTS at TJPS. Brief MVFR/IFR possible in heavier SHRA/TSRA, with mtn obscurations. VCSH lingers TJSJ/TIST/TISX ovrng into Wed. Convection wanes late this eve, with VCSH lingering TJSJ/USVI terminals. Winds LGT/VRB to calm, becoming E-ESE 10-15 kt with higher gusts/sea breeze variations aftn, then LGT/VRB ovrng.

MARINE

Issued at 428 AM AST Tue Sep 22 2026

A surface high pressure building from the north-central Atlantic will promote light to moderate east to southeast winds through the end of the week. Seas will continue today between 1 and 3 feet. A small long-period northeasterly swell will reach the area late Wednesday, and build seas between 3 to 4 feet across the Atlantic and Caribbean waters, including the local passages. Afternoon thunderstorms developing from the Atlantic and western coastal waters of Puerto Rico may produce locally strong gusts, torrential rainfall, and frequent lightning through the early evening hours each day.

BEACH FORECAST

Issued at 428 AM AST Tue Sep 22 2026

A low risk of rip currents is expected to continue across all beaches of Puerto Rico and the U.S. Virgin Islands through at least early Wednesday. 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 the arrival of a small long-period northeasterly swell, and as winds increase locally due to the sea breeze across the coastal waters.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.