textproduct: San Juan

KEY MESSAGES

Issued at 153 AM AST Sat Sep 26 2026

- Elevated flooding risk mainly during the afternoon hours across the western to northwestern sections of PR due to previous rains in those areas.

- A Heat Advisory will be in effect since 9 am through 4 PM AST across Puerto Rico and the U.S. Virgin Islands due to clear skies overnight. Heat will remain a persistent risk throughout the weekend, with the possibility of additional heat-related products being issued.

- A moderate risk of rip currents is expected to continue along northwestern to eastern beaches of Puerto Rico and northern U.S. Virgin Islands through at least Saturday night, then potentially increasing to high on Sunday into early next week.

Short Term(Today through Monday)

Issued at 153 AM AST Sat Sep 26 2026

Overnight, mostly clear skies with quiet weather prevailed across Puerto Rico and the U.S. Virgin Islands. Brief passing showers filtered portions of eastern Puerto Rico and the U.S. Virgin Islands with accumulations staying minimal. Temperatures stayed in the 70s across urban and coastal areas, while the mountainous areas observed temperatures from the upper 60s to lower 70s. Winds remained light across the islands.

The latest model guidance suggest the mid-level moisture and precipitable water values for today ranging from below normal values (25th percentile) toward near normal levels (50th percentile). Therefore, expect limited overall convection, but daytime heating, local effects, and instability associated with the nearby upper-level trough will support afternoon thunderstorms, mainly across interior and northwestern Puerto Rico. Excessive rainfall will be the primary afternoon hazard across northwestern Puerto Rico, where already saturated soils will increase the potential for urban and small- stream flooding, rapid runoff, ponding on roads, and isolated landslides or rockfalls. Excessive heat will be the other significant hazard, as mostly clear skies through the early afternoon will allow strong heating, with Heat Advisory conditions expected across susceptible areas from 9 AM through at least 4 PM today. Therefore, people are urged to stay well hydrated and take break to adequately cool if outside.

On Sunday, moisture should remain near normal values as a tropical wave approaches the area while the trough remains nearby. Although the deepest tropical moisture should stay south, stronger instability and local effects could make Sunday the most active day of the short-term period, particularly during the afternoon hours. Expect, some passing showers across windward areas, followed by thunderstorms over the interior and western to northwestern Puerto Rico, while streamers could enhance rainfall downwind of El Yunque and the smaller islands. Heavy rainfall will pose an elevated flooding risk, including water accumulation on roads and poorly drained areas, urban and small- stream flooding, and quick rises along susceptible rivers. Saturated terrains will also remain vulnerable to landslides. Thunderstorms may produce frequent lightning and gusty winds. Before convection develops, sufficient sunshine will support another day of dangerous heat across the islands.

By Monday, the weather pattern should transition toward a more typical late-September regime with no active tropical systems, with passing morning showers over eastern and windward areas and afternoon convection favoring interior and western Puerto Rico. The rainfall hazard should become more localized. Heat will continue to be a concern, especially where prolonged morning and early- afternoon sunshine occurs before showers develop, with elevated heat indices possible across coastal and urban areas. For that reason we urge people to monitor the forecast in order to ensure their safety and the safety of the once they care.

Long Term(Tuesday through Saturday)

Issued at 153 AM AST Sat Sep 26 2026

Drier conditions than those usually seen for the season are expected throughout the long term period. While model guidance indicates some variability, with the GFS showing more favorable conditions on Tuesday, the majority of the humidity will be centered in the low levels of the troposphere while drier conditions will dominate the low-to-upper levels (700-250hPa). An upper-level low pressure system will be located to the northeast of the US Virgin Islands and Puerto Rico at the beginning of the week and will shift to the southeast of the region by the end of the week eventually moving away from the CWA by the end of the forecast period. While these conditions will act to limit shower and thunderstorm activity, other factors may favor more active periods over the islands. Mid tropospheric temperatures remain favorable for the development of deep convective cells. Local effects will act as the main drivers of activity particularly over the US Virgin Islands and eastern Puerto Rico in the mornings and the interior and northwestern Puerto Rico in the afternoons. Increasing surface winds may also favor the development of streamers from the US Virgin Islands, Vieques, Culebra and El Yunque rainforest. Conditions are expected to become more enhanced by Friday afternoon when a more humid vertical profile returns increasing the potential for the development of convection. Citizens and visitors are invited to remain weather ready and stay updated of the evolving weather conditions.

The long term period might also bring a respite from the elevated heat risks and the 925 mb temperatures show a decreasing trend, suggesting more amenable conditions might prevail as the week progresses. Nonetheless, individuals are recommended to stay alert as these forecasted conditions may change.

AVIATION

(06Z TAFS) Issued at 153 AM AST Sat Sep 26 2026

Expect VFR conds across all terminals during the forecast period. Aftn SHRA/TSRA development could result in VCTS at TJBQ/TJPS btw 26/17-23Z. Brief periods of MVFR psbl across central and western PR, particularly at TJBQ aft 26/17Z. Winds LGT/VRB to calm thru 26/13Z, from E-SE 5-10 kt with higher gusts and sea breeze variations thru 26/23Z.

MARINE

Issued at 153 AM AST Sat Sep 26 2026

Light to moderate east to southeast winds of 10 to 15 knots or less and seas generally between 2 and 4 feet will prevail today. Marine conditions will gradually deteriorate from Sunday into early next week as a northerly swell spreads across the Atlantic waters and passages while easterly winds strengthen. Seas will build to 5 to 6 feet across portions of the Atlantic waters and local passages, with occasional seas up to 8 feet possible by Monday night. Small Craft Advisory conditions may become possible across portions of the Atlantic waters and local passages early next week. Scattered showers and isolated thunderstorms may also result in locally higher winds and seas, frequent lightning, and brief reductions in visibility.

BEACH FORECAST

Issued at 153 AM AST Sat Sep 26 2026

A moderate risk of rip currents will prevail today along the west- northwestern through northeastern beaches of Puerto Rico, from Mayagez to Humacao along the Atlantic coastline, as well as Culebra and the northern U.S. Virgin Islands. The moderate risk will spread to additional beaches Sunday, with a high risk of rip currents possible by Monday as a northerly swell builds, particularly along the most exposed northern beaches. Breaking waves will increase to around 5 to 6 feet during this period.

Additional beach hazards include afternoon heat and isolated thunderstorms, especially across western Puerto Rico, where lightning, brief heavy rainfall, and gusty winds may occur.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 9 AM this morning to 4 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory from 9 AM this morning to 4 PM AST this afternoon for VIZ001-002.

AM...None.