textproduct: San Juan

KEY MESSAGES

Issued at 213 AM AST Fri Sep 18 2026

- Lingering moisture from the wave and a low levels of Saharan Dust are expected today. With rainfall and thunderstorms expected over the western side of Puerto Rico during the afternoon hours.

- Seasonal conditions expected throughout the rest of the forecast period for the US Virgin Islands and Puerto Rico.

- Extreme heat risk is expected to increase across the CWA, with risk levels expected to be limited today, and significant into early next week.

- Decreasing winds will lead to amenable marine and rip current conditions throughout the rest of the forecast period.

Short Term(Today through Sunday)

Issued at 213 AM AST Fri Sep 18 2026

Another active 24 hours of rainfall across the CWA. Radar estimates show 2 to 4 inches of rain accumulation across the offshore waters, northwestern and northeastern Puerto Rico and Vieques. On the other hand portions of basins such as Carraizo and La Plata received between 1 to 2 inches of rain. These conditions continue to provide relief to the ongoing drought.

Conditions will become more seasonal into the weekend. Low concentrations of Saharan Dust have entered the US Virgin Islands and Puerto Rico overnight and will persist into early morning. A drier mid-to-low level (850 to 500 hPa) air mass will persist across the region into the early afternoon. This will act to limit rainfall activity during the early morning. However, due to the presence of breezy ESE wind flow along with lingering moisture, passing advective showers across the US Virgin Islands and eastern Puerto Rico cannot be ruled out. The atmospheric column will become more humid into the afternoon. This along with local effects will lead to the development of showers across interior and western Puerto Rico during the afternoon with a limited potential for isolated thunderstorms. Today's risk for excessive rainfall is limited which means that flooding in urban areas, roads, small streams, and washes along with a low potential for isolated flash floods is possible. Given rainfall activity during the past days, we cannot rule out the possibility of landslides over regions of high terrain, as well as across portions of northwestern Puerto Rico where the soil remains saturated from recent rainfall activity.

By Saturday into Sunday conditions are expected to become seasonal. Humid low-levels and sub-saturated mid-levels will persist both days. Conditions are expected to become less windy into the weekend with ESE wind flow. We expect the moisture coupled with local effects to lead to a pattern of isolated rainfall in the morning hours across the US Virgin Islands and eastern Puerto Rico and interior and northwestern Puerto Rico during the afternoon. The risk for excessive rainfall remains elevated through Sunday.

Due to the widespread cloud coverage over the region the heat risk for today remains limited across the coastal and urban areas. However some places might feel warmer throughout the day. We recommend individuals to keep monitoring the weather conditions as they evolve and continue checking official forums as the risk levels may be updated later during the day. The risk is expected to be significant on Saturday and Sunday. It is recommended that individuals pursuing outside activities plan accordingly and remain hydrated as they go into the weekend.

Long Term(Monday through Friday)

Issued at 213 AM AST Fri Sep 18 2026

A mid- to upper-level trough will linger over the Atlantic and northeastern Caribbean, supporting occasional induced surface perturbations throughout the period. Meanwhile, surface high pressure over the central Atlantic will maintain east to east- southeast winds and a generally wet advective pattern through much of the workweek. Passing showers will affect windward portions of Puerto Rico and the U.S. Virgin Islands, followed by afternoon showers and isolated thunderstorms over interior and western Puerto Rico. Convective development will shift according to the prevailing steering flow. However, the strongest afternoon activity will generally favor interior and western Puerto Rico, where a limited flooding rain threat may develop each afternoon. The flooding threat elsewhere across the islands will be reassessed as the period approaches.

A warming trend will continue at least during the first half of the week. Near- to above-normal moisture, combined with limited ventilation across urban and coastal areas, could result in periods of elevated to locally significant heat risk. Guidance then indicates a drying trend during the latter part of the week as precipitable water decreases to near or below normal levels.

The upper-level trough will also maintain strong vertical wind shear across the region, creating an unfavorable environment for tropical cyclone development. Local sea-breeze variations are expected during the day, with land-breeze influences possible overnight along coastal areas.

AVIATION

(06Z TAFS) Issued at 213 AM AST Fri Sep 18 2026

Mostly VFR conds expected through the period. However, SHRA/TSRA will likely affect TJBQ and the vicinity of TJSJ/TJPS, with brief MVFR/IFR psbl at TJBQ. VCSH expected across USVI terminals and TJSJ after 18/23Z. Light and variable wind becoming E-ESE winds at 10-15 kt with gusts after 18/13Z. Light and variable winds return after 18/23Z.

MARINE

Issued at 213 AM AST Fri Sep 18 2026

A surface high pressure system over the western into central Atlantic will dominate the regional weather pattern, leading to gentle to moderate east-southeasterly winds for the next few days. Tropical moisture will move over the area later today into the weekend and early next week, enhancing the potential for isolated thunderstorms and localized hazardous marine conditions.

BEACH FORECAST

Issued at 213 AM AST Fri Sep 18 2026

A moderate risk of rip currents will be in effect today along northern Puerto Rico beaches, with low risk elsewhere. As winds diminish, the rip current risk will drop to low across all local beaches through early next week, returning to moderate by midweek as winds strengthen. Despite the lower overall risk, localized life- threatening rip currents remain possible near piers, groins, reefs, and jetties. Additionally, daily diurnal convection will continue to generate afternoon showers and isolated thunderstorms across western and northwestern Puerto Rico, bringing localized hazards of lightning and gusty winds. Beachgoers should monitor changing conditions and seek shelter immediately. Additionally, an elevated to significant heat risk is forecast over the coming days, enhancing potential heat impacts. Residents and visitors should remain hydrated and limit prolonged sun exposure during peak afternoon heating. Follow guidance from local health officials.

SJU WATCHES/WARNINGS/ADVISORIES

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