textproduct: San Juan

KEY MESSAGES

Issued at 330 AM AST Sun Oct 4 2026

- A Heat Advisory is in effect from 10 AM to 4 PM AST this afternoon across Puerto Rico and the U.S. Virgin Islands. Heat will likely remain a persistent risk over the coming days, particularly before the development of afternoon rain and in areas where rainfall remains limited.

- Showers and thunderstorms posing a limited to elevated flood risk will continue to develop this afternoon and into early next week, mainly across the interior and western Puerto Rico.

- The potential for more widespread activity will increase from Wednesday into Thursday as moisture associated with a tropical wave moves into the region. This could increase the risk of locally heavy rainfall, flooding, and stronger thunderstorms.

- There is a moderate risk of rip currents along the northern and eastern beaches of Puerto Rico and Culebra today. Similar conditions are expected to persist over the coming days, but the risk will also extend to the beaches of the U.S. Virgin Islands.

Short Term(Today through Tuesday)

Issued at 330 AM AST Sun Oct 4 2026

Overall, conditions remained relatively calm overnight, with partly cloudy skies and light, variable winds. Passing showers affected the local waters and windward portions of Puerto Rico and the U.S. Virgin Islands, although radar estimates indicated no significant rainfall accumulations since midnight. More frequent showers and thunderstorms were observed farther north across the Atlantic waters and near Hispaniola, where a mid- to upper-level trough remained present. Surface observations and weather stations reported minimum temperatures generally in the upper 70s to lower 80s.

The forecast for today, Sunday, is expected to feature a typical diurnal weather pattern, with winds gradually becoming more east- southeasterly. An upper-level trough will remain positioned near Hispaniola, keeping Puerto Rico along its eastern flank and providing only limited large-scale support. Latest satellite- derived Precipitable Water (PWAT) imagery indicates that values will remain near seasonal levels, ranging from 1.7 to 1.9 inches, although some drier air is present between approximately 700 and 500 mb as a mid level ridge begind to set. As a result, afternoon showers and thunderstorms will be driven mainly by local effects such as daytime heating, sea-breeze interactions, and available moisture, with the greatest activity expected across the Cordillera Central and western to northwestern Puerto Rico.

This afternoon, an elevated flood threat remains in place, particularly across portions of the interior and western to northwestern Puerto Rico. A limited flood threat remains across portions of eastern Puerto Rico and the metropolitan area due to the potential development of El Yunque and U.S. Virgin Islands streamers. An elevated flood threat means flooding is possible in urban areas, along roads, and in small streams and washes, while a limited flood threat indicates that ponding of water is possible on roads and in poorly drained areas. Similar conditions are expected on Monday and Tuesday. Mornings should remain relatively quiet, with only limited shower activity. During the afternoon, convection is expected to increase as lingering low-level moisture combines with daytime heating, local terrain effects, and sea- breeze interactions.

Heat concerns will persist today and are likely to extend into early next week as temperatures in the lower levels of the atmosphere continue to rise. Guidance indicates 925-mb temperatures near the 75th percentile, or approximately two standard deviations above normal. The primary concern during the late morning and early afternoon will be heat, followed by an increasing threat of localized heavy rainfall and flooding where thunderstorms develop. Residents and visitors are encouraged to remain hydrated and stay weather aware, as conditions may change rapidly during the afternoon.

Long Term(Wednesday through Sunday)

Issued at 330 AM AST Sun Oct 4 2026

A tropical wave crossing the local area Wednesday into Thursday will bring the best opportunity for showers and thunderstorms during the long-term forecast period. Precipitable water (PWAT) values will increase to 2.1-2.3 inches, which is above average for this time of year. Despite the wave, mid- to upper-level support is not expected to be very favorable. A mid-level ridge to the north will keep mid-level lapse rates only modestly steepened with little cooling at 500 mb. Meanwhile, an upper-level trough just northeast of the local area could produce some upper-level divergence. However, guidance disagrees on the exact positioning of the trough. Models also suggest an upper-level ridge just south of the region that could shield the area from upper-level divergence.

Regardless, a more active pattern is expected Wednesday, Wednesday night, and into Thursday. Windward sections will experience more frequent showers and isolated thunderstorms. Active afternoons are also anticipated, with scattered to numerous showers across the interior to western and northwestern portions of the islands. An elevated flood threat exists for those areas, while a limited flood threat remains across eastern Puerto Rico and the USVI as rounds of showers cross the area. The steering flow is expected to be mainly easterly on Wednesday, shifting to southeasterly on Thursday as the wave axis crosses the area.

As the wave departs, a transition to drier conditions and a return of easterly flow is expected late Thursday onward, with the mid- to upper-level ridge providing increased stability and drier air aloft. Therefore, a seasonal pattern returns late Thursday into the early weekend, featuring typical passing showers across windward areas during the overnight and morning hours, followed by afternoon convection across interior to western Puerto Rico driven by diurnal heating and local effects. A limited flood threat will continue each afternoon for those areas. Rain streamers will also be possible each afternoon downwind from El Yunque, the USVI, Vieques, and Culebra.

A limited heat threat is expected throughout the long-term period. Extremely sensitive individuals could be affected and should take precautions to protect themselves from heat conditions.

AVIATION

(06Z TAFS) Issued at 330 AM AST Sun Oct 4 2026

Mainly VFR conds are expected across all terminals through the forecast period. Passing -SHRA/VCSH across TJSJ and the USVI terminals during the morning hrs. Aft 04/16-17Z, SHRA/TSRA are expected to develop across the interior and W/NW PR, producing VCTS at TJBQ/TJPS and TJSJ. Expect intermittent/brief MVFR conds due to vis reductions and mountain obsc. E-ESE winds will increase aft 13Z to 10-12 kt, with sea breeze variations and slightly higher gusts. Light and variable winds overnight.

MARINE

Issued at 330 AM AST Sun Oct 4 2026

Surface high will shift toward the east on Sunday, relaxing the pressure gradient a little. As a result, winds will become light to moderate and seas will gradually subside. Easterly trade winds are expected to strengthen again by Tuesday into Wednesday as another surface high builds across the western Atlantic, resulting in increasingly choppy marine conditions. A tropical wave will move over the Caribbean Sea late Wednesday into Thursday, increasing the potential for showers and thunderstorms.

BEACH FORECAST

Issued at 330 AM AST Sun Oct 4 2026

For the north and east facing beaches of the local islands, the risk of rip currents will be moderate today, and low on Monday. The risk elsewhere will be low.

There is a risk of lightning each afternoon across the local beaches, mostly in the western and northern half of Puerto Rico. Seek shelter immediately if thunder is heard.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for VIZ001-002.

AM...None.