textproduct: San Juan

KEY MESSAGES

Issued at 241 PM AST Thu Oct 8 2026

- Excessive heat will remain a concern over the next several days, as warm temperatures and elevated heat indices increase the risk of heat-related illnesses.

- An increase in atmospheric instability is forecast from late Sunday into the upcoming workweek, increasing the potential for flooding and lightning across the region throughout much of the long-term period.

- For the U.S. Virgin Islands, excessive heat will be the primary threat over the next two days.

Short Term(This evening through Saturday)

Issued at 241 PM AST Thu Oct 8 2026

Passing showers moved across portions of the U.S. Virgin Islands and eastern Puerto Rico during the morning hours, driven by an east-southeast wind flow and lingering moisture from a distant tropical wave well to the west. By noon, the San Juan streamer began to develop, affecting portions of San Juan, Guaynabo, and Catano. Doppler-radar-estimated rainfall accumulations of up to 0.60 inches. Maximum temperatures remained in the upper 80s to low 90s across coastal and urban areas, while the central mountain range of Puerto Rico reached the low 80s. Winds prevailed mainly from the east-southeast at 10 to 15 mph, with higher gusts and sea breeze variations.

For the rest of the afternoon and into the evening, abundant tropical moisture combined with daytime heating and local effects will bring showers and thunderstorms to central, western, and northwestern Puerto Rico. Because recent rains have already saturated the soil, any additional rainfall could trigger urban and small-stream flooding, quick river rises, and landslides, particularly across northwestern Puerto Rico. Additional showers could also develop across the San Juan metropolitan area. Shower and thunderstorm activity will diminish before sunset, moving into a calmer, more stable night.

Weather conditions will gradually improve on Friday as drier air filters over the islands, bringing precipitable water (PWAT) values below normal to around 1.50 inches alongside mid- to upper-level ridging. As the surface high-pressure system over the central Atlantic migrates eastward, winds will shift to the east in the morning and east-northeast by the afternoon, bringing slightly cooler temperatures and breezy conditions. Under this pattern, daytime heating and local effects will spark afternoon showers and isolated thunderstorms across central, western, and southwestern Puerto Rico.

By Saturday, conditions will transition back to a wetter pattern as an upper-level low positions east of the islands, increasing instability aloft and raising the potential for thunderstorms across the region. Although the overall heat risk will remain limited over the next few days, warm temperatures will persist, and residents and visitors are encouraged to stay hydrated and seek shade during peak afternoon heat.

AVIATION

(18Z TAFS) Issued at 241 PM AST Thu Oct 8 2026

Aftn SHRA/TSRA will continue to develop and spread across portions of interior PR to W-NW PR thru 08/23Z. Brief MVFR/IFR conds are possible in heavier SHRA/TSRA, along with mtn obsc, particularly at TJBQ from around 08/19-08/21Z. Additional SHRA will result in VCSH/-SHRA at TJSJ & TJPS thru 08/22Z. Locally reduced VSBY, LTG, lower CIGs and gusty/VRB winds possible. ESE winds 10-15 kt thru 08/00Z, becoming light/VRB overnight an increasing again at 09/14Z from the E.

SJU WATCHES/WARNINGS/ADVISORIES

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