textproduct: San Juan

KEY MESSAGES

Issued at 227 PM AST Mon Oct 26 2026

- A Heat Advisory remains in effect until 5 PM AST this afternoon for Puerto Rico and the U.S. Virgin Islands. Hot and humid conditions will increase the risk of heat-related illnesses, especially for individuals without adequate cooling or hydration. Elevated heat impacts are expected to persist through Tuesday.

- Dangerous marine and coastal conditions continue across the coastal waters and beaches of western, northern, and eastern Puerto Rico, as well as Culebra, due to incoming pulses of northerly swell. Small Craft Advisories, a High Rip Current Risk, and High Surf Advisories are in effect. Please refer to the Marine and Beach Forecast sections below for specific details.

- A drying trend is anticipated over the coming days, bringing generally fair weather across Puerto Rico and the U.S. Virgin Islands. However, pockets of low-level moisture will bring occasional passing showers, primarily across northwestern, southern and southeastern Puerto Rico during the afternoon and overnight hours. A few isolated thunderstorms cannot be ruled out.

Short Term(This evening through Wednesday)

Issued at 227 PM AST Mon Oct 26 2026

A southeasterly advective pattern prevailed across the region this morning, with a few passing showers affecting mainly the southeastern coastal areas of Puerto Rico. Otherwise, mostly fair weather conditions prevailed across much of the region, allowing temperatures to rise quickly. By noon, several weather stations across southwestern and north-central Puerto Rico had already reached Heat Advisory criteria, with hot and humid conditions expected to maintain an increased heat risk through the rest of the afternoon.

For the remainder of today, southeasterly flow will continue to transport moisture across the region, with precipitable water gradually increasing toward 1.8 to 1.9 inches. However, a ridge at the mid and upper levels, accompanied by relatively warm temperatures aloft, dry mid-levels, and modest lapse rates, will limit deep convection. Although daytime heating, sea breeze convergence, and local effects could still support isolated afternoon showers and thunderstorms across the interior and northwestern Puerto Rico, confidence in convective coverage remains low. Meanwhile, persistent southeasterly flow will favor additional showers across southern and southeastern Puerto Rico, where locally heavy rainfall could lead to ponding of water on roads and in poorly drained areas, as well as isolated urban and small-stream flooding. Similar activity could affect Vieques and the surrounding southern waters.

On Tuesday, a trough over the western Caribbean and a ridge over the eastern Caribbean will maintain a southeasterly flow, continuing to transport tropical moisture across the region. Both GFS and ECMWF guidance suggest precipitable water increasing toward 1.9 to 2.0 inches, with relatively high moisture content at low levels. Nevertheless, the persistent ridge aloft and relatively warm 500-mb temperatures will maintain modest mid-level lapse rates, limiting widespread deep convection despite the increasing moisture. While local effects and daytime heating could support isolated afternoon thunderstorms across portions of the interior and northwestern Puerto Rico, uncertainty remains regarding their coverage and intensity. Recent NBM and ECMWF ensemble rainfall guidance suggests a greater potential for rainfall across southern and southeastern Puerto Rico and the surrounding southern waters, including portions of the smaller islands. Locally heavy or repeated showers could result in ponding of water in roadways and in poorly drained areas, particularly across southern and southeastern Puerto Rico.

By Wednesday, a gradual weakening of the ridge aloft will allow 500- mb temperatures to cool and mid-level lapse rates to steepen slightly, potentially providing a more favorable environment for convection. However, both GFS and ECMWF guidance indicate decreasing moisture, with considerable differences in the magnitude of drying. While the GFS maintains precipitable water generally between 1.6 and 1.8 inches, the ECMWF suggests a more pronounced dry intrusion, with values dropping toward 1.3 to 1.5 inches. This introduces uncertainty regarding the coverage and intensity of showers and thunderstorms. Nevertheless, lingering moisture, daytime heating, and local effects could still support afternoon convection across portions of Puerto Rico, particularly where sufficient moisture persists. The wetter GFS solution would favor greater convective coverage, while the drier ECMWF solution would limit rainfall activity despite gradually improving lapse rates.

Above-normal temperatures and humid conditions will maintain an heat risk through Tuesday, particularly across coastal and urban areas of Puerto Rico and the U.S. Virgin Islands. Some relief is anticipated by Wednesday as drier air moves into the region, although temperatures will remain warm, especially across coastal and urban areas.

Long Term(Thursday through Monday)

Issued at 353 AM AST Mon Oct 26 2026

No major changes were introduced to the long-term forecast, as wetter and more unstable conditions continue to be forecast this weekend. The latest model guidance continues to suggest a surface high pressure over the Central Atlantic interacting with a polar trough deepening into the tropics, maintaining an ESE-SE wind flow throughout the forecast period. A mid-to-upper level ridge northeast of the CWA should continue to dominate the weather pattern on Thursday, as guidance suggests warmer-than-normal 500 mb temperatures (above -6 C) and low mid level lapse rates, indicating unfavorable conditions for deep convection. Additionally, the Galvez- Davison Index (GDI) suggests shallow convection on Thursday afternoon across the mountain ranges of Puerto Rico. As mentioned in the previous discussions, PWAT values should remain below climatological normal (below 1.75 inches), with the dry slot in the low and mid levels. Although daytime heating combined with local effects and sea breeze convergence should aid in breaking the cap inversion and allow shower and thunderstorm activity, rainfall accumulations should remain minimal.

Friday onwards, global models continue to suggest wetter and unstable conditions across the CWA, as the trough approached the CWA, weakening the ridge, leading to divergence aloft and enhancing instability. Additionally, the latest NCICS forecast continues to suggest the Madden-Julian Oscillation (MJO) over the CWA, which may enhance upward motion and divergence aloft. The latest deterministic guidance from the GFS and ECMWF suggests PWAT values could reach up to 2.25 inches, slightly above normal, mainly in the low and mid levels. Additionally, the guidance suggests skinny-sounding profiles, with high CAPEs, and cooler- than-normal mid-level temperatures (between -6 and -8 C), and stronger upper- winds, allowing cloud growth and ventilation. Therefore, the most likely scenario remains, with an advective pattern across windward sections of the islands early Saturday, followed by deep afternoon convection across mountain ranges of Puerto Rico, including the San Juan Metro Area. Rainfall accumulations could lead to urban and small stream flooding, without ruling out flash flooding. Additionally, rivers may rise quickly. Therefore, the flood threat will remain limited to elevated across the aforementioned areas on Friday, Saturday, and Sunday. Besides flooding, thunderstorms could produce gusty winds and frequent lightning.

AVIATION

(18Z TAFS) Issued at 227 PM AST Mon Oct 26 2026

Mainly VFR conds expected across all terminals thru the fcst period. SE winds at 10-15 kt with hir gusts thru 22Z, bcmg lgt overnight. VCSH expected at TJSJ/TJBQ thru 22Z, with -SHRA at TJPS thru 02Z and brief MVFR conds psbl thru 27/10Z. ESE-SE winds at 10-15 kt expected Tue with gusts up to 20 kt across eastern terminals.

MARINE

Issued at 227 PM AST Mon Oct 26 2026

Surface high pressure over the central Atlantic will promote moderate to locally fresh east-to-southeasterly winds across the region through midweek. A long-period northerly swell is expected to spread across the Atlantic waters and local passages today, building seas to 6 to 8 feet through Tuesday. Small Craft Advisories remain in effect for the Atlantic offshore waters and the Mona Passage through Tuesday afternoon. Isolated thunderstorms are forecast to develop mainly over Caribbean waters, the Mona Passage, and offshore Atlantic waters over the next few days.

BEACH FORECAST

Issued at 227 PM AST Mon Oct 26 2026

A long-period northerly swell will arrive today, with additional pulses expected through midweek. This swell will generate breaking waves of 6 to 12 feet, creating rough surf and life-threatening rip currents, primarily along north-facing beaches of Puerto Rico, Culebra, and the northern U.S. Virgin Islands. A High Rip Current Risk remains in effect for the western, northern and eastern beaches of Puerto Rico and Culebra through at least Tuesday afternoon. A High Surf Advisory is also in effect for the northwestern to northern coastline of Puerto Rico through late tonight. Beachgoers are strongly urged to stay out of the water at beaches under these advisories and to heed all warning flags, posted signs, and instructions from lifeguards and local officials. Although the High Surf Advisory is currently in effect through late tonight, an extension is likely.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through Tuesday afternoon for PRZ001-002- 005-008-010-012.

High Surf Advisory until 6 AM AST Tuesday for PRZ001-002-005-008- 010.

Heat Advisory until 5 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...Small Craft Advisory until 6 PM AST Tuesday for AMZ711.

Small Craft Advisory from 6 PM this evening to 6 PM AST Tuesday for AMZ712-741-742.