textproduct: San Juan

KEY MESSAGES

Issued at 117 AM AST Thu Sep 24 2026

- Shower and thunderstorm activity is expected to increase today across Puerto Rico and U.S. Virgin Islands due to the combination of moisture from a tropical wave and an induced surface through. This could enhance the risk of small and urban flooding, isolated flash flooding and landslides on areas where terrain is already saturated from rainfall over the past days.

- Heat-related risks will continue each day and into the weekend. Heat-sensitive individuals should avoid outdoor activities and stay hydrated.

- A drier air mass will approach our local area by Friday extending into Saturday, slightly limiting showers and thunderstorm development over the islands.

- A moderate rip current risk will be in effect today, extending through the weekend.

Short Term(Today through Saturday)

Issued at 117 AM AST Thu Sep 24 2026

An increase in shower and thunderstorm activity have been observed overnight as a surface disturbance approaches the CWA, with some of these activity reaching eastern and northern coastal areas. Temperatures have fallen overnight between the high 70s to low 80s over coastal areas, while interior observations have reported temperatures between mid 60s and low 70s.

This morning, brief showers and isolated thunderstorms are possible across eastern Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands. Enhanced instability is likely later this afternoon across the region, as a surface through induced by a lingering Tropical Upper-Level Through (TUTT) and moisture associated to a tropical wave reaches the islands. This scenario, combined with daytime heating, local effects and a ESE flow, will favor the development of stronger showers and thunderstorms over eastern, northern and northwestern portions of Puerto Rico, while isolated activity is possible elsewhere. By Friday, upper-level divergence from the TUTT will continue to support slightly favorable conditions for showers and thunderstorms development. Although, a drier airmass approaching the islands could limit deep convection, as a result afternoon convection could be more localized, mainly over north to northwestern portions of Puerto Rico. Moving into the weekend, the drier air mass will settle over the CWA, dragging in low concentrations of Saharan Dust. Thus, expect a pattern similar to Friday.

Overall, the primary weather hazards will include localized heavy rainfall, and isolated thunderstorms, which could be accompanied by frequent lightning and strong wind gusts, particularly today. A limited to elevated excessive rainfall risk is expected today as conditions become more favorable for stronger convection, and limited on Friday and Saturday as a result of a drier air mass over the islands. Consequently, shower activity today may lead to water ponding on roadways, urban and small stream flooding, and even isolated flash floods with periods of heavy rainfall, alongside a continued risk of landslides where terrain is already saturated from recent rainfall.

An elevated excessive heat risk is likely on Saturday as drier air will limit cloud cover over the islands, while it remains limited on today and Friday.

Long Term(Sunday through Thursday)

Issued at 117 AM AST Thu Sep 24 2026

The weather conditions over the long term period will continue to be influenced by several synoptic features. Over the eastern Atlantic ocean a low level high pressure system will promote an ENE wind flow. The conditions are expected to become breezy to locally windy across the US Virgin Islands and Puerto Rico from Monday into mid- week. Additionally, a lingering upper-level low pressure system located to the east of the CWA will continue to drive upper-level convergence through mid-to-late next week. This will act to limit the potential for the development of deep convection over the region. On the other hand, while a tropical wave is expected to reach the forecast region between Monday and Tuesday the moisture field associated with the system will remain to the north and south of the US Virgin Islands and Puerto Rico with lower than average precipitable water (PWAT) values intruding the region. Nonetheless, on Monday the atmospheric column is expected to be moister than most of the days in the long term period. Coupled with local effects, the day is expected to be favorable for the development of isolated shower and thunderstorm activity.

Given that the synoptic features are currently acting to limit weather activity, the day-to-day is expected to be driven primarily by local effects with seasonal conditions dominating the observed weather pattern through late next week. With rainfall activity expected over the US Virgin Islands and eastern Puerto Rico in the morning and over the interior and northwestern Puerto Rico during the afternoon. Weather conditions will become more favorable by Thursday, with a more humid vertical profile returning. Mid- tropospheric temperatures are also forecasted to be below -6 degrees Celsius, increasing the potential for the development of deep convective cells. Risks associated to extreme heat continue to be one of the main concerns throughout the rest of the forecast period with 925 mb temperatures expected to be 2 standard deviations above normal ranges for the season into early next week. As individuals prepare for the weekend it is recommended to adjust outside activities and events accordingly and to remain hydrated. Citizens ands visitors are invited to stay alert of the evolving weather conditions as we move into the weekend.

AVIATION

(06Z TAFS) Issued at 117 AM AST Thu Sep 24 2026

Mainly VFR conds are expected across all terminals during the forecast period. However, aftn SHRA/TSRA development could result in brief periods of MVFR/IFR with mtn obscurations across central and western PR, affecting TJBQ/TJPS/TJSJ aft 24/17Z. VCSH lingers TJSJ/TIST/TISX overnight into Friday. Winds LGT/VRB to calm thru 24/14Z, becoming E-ESE 10-15 kt with higher gusts and sea breeze variations thru 24/23Z, then LGT/VRB overnight.

MARINE

Issued at 117 AM AST Thu Sep 24 2026

Light to moderate east to southeast winds will prevail across the regional waters, with seas generally between 2 and 4 feet. A weak long-period northeasterly swell will continue to spread across the local Atlantic waters and passages, gradually increasing seas through the weekend. Meanwhile, an upper-level trough interacting with a weak tropical wave will support increased shower and thunderstorm activity today, with thunderstorms capable of producing locally strong wind gusts, frequent lightning, and brief reductions in visibility.

BEACH FORECAST

Issued at 117 AM AST Thu Sep 24 2026

A moderate risk of rip currents will continue along the north- and east-facing beaches of Puerto Rico and the U.S. Virgin Islands through the weekend. Northerly to northeasterly swells will gradually increase the risk, with high rip current conditions likely at some northern exposed beaches late this weekend into early next week.

Beachgoers should also be alert for hot conditions and periods of showers and thunderstorms. Thunderstorms may produce frequent lightning, gusty winds, and rapidly changing beach conditions. If thunder is heard, leave the water and seek shelter immediately.

SJU WATCHES/WARNINGS/ADVISORIES

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