textproduct: San Juan

KEY MESSAGES

Issued at 203 PM AST Fri Oct 9 2026

* A limited to elevated flooding threat is expected for tomorrow along western and southwestern PR.

* A limited heat threat is expected for the upcoming days during the weekend.

* An increase in instability is expected as an upper-level low moves over the region, increasing the flood and lightning threat from Monday into Wednesday.

* There is a low risk of rip currents across all the coastal areas.

Short Term(This evening through Sunday)

Issued at 203 PM AST Fri Oct 9 2026

A tranquil weather pattern was observed during the morning hours today, with little to no cloudiness or shower activity across the islands. Satellite imagery showed mostly clear skies until around 11 AM AST, when clouds began to develop, followed by showers along the Cordillera Central. By 1 PM AST, showers had increased in frequency and coverage, with streamers extending from Culebra and Vieques into mainland Puerto Rico and moving westward under the easterly wind flow. Showers were more significant across the western interior, with rainfall accumulations remaining below one inch due to their rapid movement. Daytime temperatures were in the low 90s across coastal areas and portions of the western interior and in the low 80s across mountainous areas.

For the rest of the evening, relatively dry conditions will favor limited shower activity and cloudiness across the islands. However, a few passing showers may affect eastern Puerto Rico and the U.S. Virgin Islands as moisture gradually increases overnight. On Saturday, east to northeast winds will prevail as an induced surface perturbation moves over the region and supports increasing moisture. According to the latest GFS guidance, precipitable water will rise to around 2.1 inches Saturday morning, near the 75th climatological percentile, while relative humidity increases through the lower and middle levels. This moisture will favor passing morning showers across windward coastal areas, followed by afternoon development across western and southwestern Puerto Rico due to daytime heating and local effects. Locally heavy showers may result in ponding of water on roads and in poorly drained areas. However, limit thunderstorm development is expected, with a limited lightning threat associated with the strongest convection. Moisture will gradually decrease later Saturday, favoring a reduction in shower coverage during the evening. Heat threat is not expected to pose a significant threat across most of the region, as easterly winds and decreasing low-level temperatures will favor more seasonable conditions and heat indices generally below 108F.

On Sunday, a broad surface high-pressure system over the western Atlantic will maintain easterly surface winds as an easterly wave approaches the region. Precipitable water values will fluctuate between approximately 1.8 and 1.9 inches through the morning before decreasing later in the day. Available moisture will support passing showers across eastern Puerto Rico and the U.S. Virgin Islands, followed by afternoon convection over interior and western Puerto Rico. GFS guidance indicates falling upper-level heights and cooling temperatures at 500 mb to around 7C. These will suggest a more favorable environment for deeper convection, particularly as the upper-level feature moves closer to the region. The combination of available moisture, daytime heating, and local effects will support showers and isolated thunderstorms, with localized ponding of water and lightning possible with the strongest activity.

AVIATION

(18Z TAFS) Issued at 203 PM AST Fri Oct 9 2026

Mainly VFR conds will continue across all TAF sites during the forecast period. Aftn SHRA/TSRA will develop across the central mountain range and move over portions of the interior to W-SW PR, affecting mostly TJPS thru 09/23Z. Additional SHRA will result in VCSH/-SHRA at TJSJ/TIST/TISX thru 09/23Z. E winds 15-20 kt with higher gusts and seas breeze variations thru 09/23Z, becoming light/VRB overnight.

MARINE

Issued at 203 PM AST Fri Oct 9 2026

A weak surface high pressure over the central Atlantic will continue to drift eastward and displaced by a frontal boundary moving east across the western Atlantic. This will continue to result in weak pressure gradient, maintaining mainly gentle to moderate easterly trade winds. Another surface high-pressure will build across the western Atlantic over the weekend, sustaining moderate to locally fresh easterly trade winds. An induced surface trough will move near the region from Saturday onwards, promoting an increase in showers and thunderstorms across the local waters.

BEACH FORECAST

Issued at 203 PM AST Fri Oct 9 2026

A low risk of rip currents will continue across all beaches of Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands through early next week. Although the risk is low, beachgoers are encouraged to pay attention to beach conditions as life-threatening rip current can occur in the vicinity of jetties, piers, reefs, and groins. In addition, beachgoers must remain weather alert, as shower and thunderstorm activity is expected each day, particularly near the western coastal areas of the islands.

SJU WATCHES/WARNINGS/ADVISORIES

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