textproduct: San Juan

KEY MESSAGES

Issued at 140 AM AST Wed Oct 21 2026

* A relatively quiet and warm day will give way to wetter conditions as a surge of tropical moisture sweeps across the region Thursday through the weekend. More frequent showers and thunderstorms, including nighttime activity, may produce lightning, gusty winds, and locally heavy rainfall capable of causing flooding.

* A high risk of rip currents continues through this afternoon as northerly swell subsides. Conditions briefly improve Thursday before another swell brings renewed rip current hazards and potentially hazardous seas for small craft Friday into the weekend.

* Warm temperatures today may affect individuals sensitive or vulnerable to heat. Another period of warmer weather is possible Sunday into Monday.

Short Term(Today through Friday)

Issued at 140 AM AST Wed Oct 21 2026

Slow-moving to nearly stationary strong thunderstorms developed over the Atlantic waters north of Puerto Rico overnight, producing frequent lightning and heavy downpours, with possible waterspouts and locally hazardous seas. This activity should gradually diminish after sunrise, with daytime heating shifting shower and thunderstorm development toward the interior and northern to northwestern portions of Puerto Rico during the afternoon. Light southeasterly steering winds will favor slow-moving convection, particularly where sea-breeze convergence and local terrain effects enhance development. However, relatively dry air and below-normal moisture should limit overall coverage. Greater sunshine will favor warmer temperatures, particularly across coastal and urban areas. Tonight, deeper tropical moisture will begin spreading northward across the Caribbean waters, supporting an increase in overnight showers and thunderstorms.

A wetter and more active pattern is expected Thursday and Friday as tropical moisture spreads across the region. Model guidance indicates precipitable water values increasing to around 2.2 to 2.3 inches, well above normal, with some additional support from an upper-level trough. Although increasing cloudiness may limit daytime heating, passing showers and locally driven convection should favor scattered to numerous showers and thunderstorms, with activity peaking during the afternoon as daytime heating, sea- breeze convergence, and terrain effects enhance development. Some of this activity may persist into the evening, while additional showers and thunderstorms may develop overnight, particularly over the surrounding waters and near coastal areas where land-breeze convergence occurs. Winds will gradually shift toward a more easterly to southeasterly direction Thursday and Friday, remaining generally gentle to moderate, with locally fresh winds possible across the Caribbean waters and southern coastal areas beginning Thursday afternoon.

The main hazards Thursday and Friday will include frequent lightning, gusty thunderstorm winds, and locally heavy rainfall. Ponding of water on roads and in poorly drained areas will be possible across Puerto Rico and the U.S. Virgin Islands, while slow-moving or repeated thunderstorms could lead to urban and small-stream flooding and isolated flash flooding. As rainfall accumulates over several days, the risk of landslides will gradually increase, particularly in steep terrain. These hazards may extend into the evening and overnight hours. Although confidence remains high in a wetter pattern, uncertainty persists regarding where the heaviest rainfall will occur.

Long Term(Saturday through Wednesday)

Issued at 140 AM AST Wed Oct 21 2026

Wet and unsettled weather conditions are expected across Puerto Rico and the U.S. Virgin Islands on Saturday, followed by gradual improvement Sunday and a transition toward a drier and more stable weather pattern early next week.

A southeast to southerly flow, maintained by a deep-layer low exiting the eastern coast of the United States and surface high pressure across the central Atlantic, will continue to transport tropical moisture into the region. Latest GFS guidance indicates precipitable water values above 2 inches and elevated mid-level relative humidity through Saturday, supporting scattered to numerous showers and thunderstorms. Daytime heating, sea-breeze convergence, and local terrain effects will favor the greatest convective activity across interior, northern, and western Puerto Rico. Increasing steering winds should promote more progressive showers and thunderstorms, although periods of heavy rainfall remain possible. Some activity may persist into the evening, with additional showers and thunderstorms developing overnight over the surrounding waters and coastal areas. The main hazards Saturday will include frequent lightning, locally heavy rainfall, and gusty thunderstorm winds. Heavy downpours could lead to ponding of water on roadways, reduced visibility, urban and small-stream flooding, and isolated flash flooding, particularly where repeated showers occur. As rainfall accumulates over several days, the concern for landslides will also increase, especially in areas of steep terrain.

By Sunday, a gradual decrease in moisture should result in reduced shower coverage. However, lingering moisture and local effects will continue to support afternoon thunderstorms, particularly across interior and western Puerto Rico. Weakening steering winds may allow some thunderstorms to move slowly, increasing the potential for localized rainfall accumulations and isolated flooding despite the overall improving trend.

A more noticeable improvement is expected Monday through Wednesday as drier air spreads through the atmospheric column and subsidence associated with a strengthening mid-level ridge suppresses widespread convective development. Model guidance continues to support this transition, with below-normal precipitable water values and substantially lower mid-level relative humidity. Although passing showers and isolated afternoon convection will remain possible, the potential for widespread heavy rainfall and flooding should decrease considerably.

AVIATION

(06Z TAFS) Issued at 140 AM AST Wed Oct 21 2026

Strong, slow-moving TSRA over the Atl waters N of PR should gradually diminish aft sunrise, with VCSH/VCTS psbl near TJSJ/TJPS and USVI terminals. VFR conds expected to prevail overnight. Aftn SHRA/TSRA may produce brief MVFR/IFR cigs/vsbys at TJSJ/TJBQ, mainly due to +RA and low cigs. Activity should diminish aft 21/23Z. Sfc winds light/VRB overnight, bcmg SE at 5-10 kt aft 21/13Z, with sea-breeze variations and locally gusty winds near TSRA.

MARINE

Issued at 140 AM AST Wed Oct 21 2026

Light to gentle southeasterly winds will gradually become more easterly and increase to moderate to locally fresh speeds toward the end of the week and into the weekend, particularly across the Caribbean waters. A long-period northerly swell continues to subside, allowing seas to gradually improve. However, another swell arriving Friday will likely bring hazardous seas for small craft through the weekend and into early next week. Increasing tropical moisture will also favor more frequent showers and thunderstorms, including nighttime activity, with lightning, gusty winds, and reduced visibility.

BEACH FORECAST

Issued at 140 AM AST Wed Oct 21 2026

A High Risk of Rip Currents remains in effect through this afternoon along north-facing beaches of Puerto Rico, Culebra, St. Thomas, and St. John. Conditions should briefly improve as the current northerly swell subsides. However, another swell arriving Friday will likely bring a renewed high risk of rip currents and possible high surf impacts along exposed northern beaches through the weekend and into early next week. Beachgoers should avoid swimming at affected beaches and stay away from exposed rocks and jetties. Showers and thunderstorms may also bring lightning and gusty winds to coastal areas.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through this afternoon for PRZ001-002-005- 008-010-012.

VI...High Rip Current Risk through this afternoon for VIZ001.

AM...None.