textproduct: San Juan

KEY MESSAGES

Issued at 159 PM AST Wed Oct 21 2026

- Weather conditions will become increasingly wet and unstable tonight through the weekend, with more frequent showers and thunderstorms, including during the nighttime hours.

- Periods of heavy rainfall may lead to ponding of water on roads, urban and small-stream flooding, rapid river rises, and isolated flash flooding. Thunderstorms may also produce frequent lightning and gusty winds. Landslides will become an increasing concern in areas receiving repeated rainfall.

- A High Risk of Rip Currents continues through this evening along north-facing beaches. Conditions will briefly improve Thursday before another swell brings a renewed high rip current risk Friday through the weekend, with potentially hazardous breaking waves. Beachgoers should avoid swimming at affected beaches.

- More frequent showers and thunderstorms Thursday through the weekend will increase the risk of lightning near beaches and coastal areas. Seek shelter indoors when thunderstorms approach.

Short Term(This evening through Friday)

Issued at 159 PM AST Wed Oct 21 2026

A relatively stable weather pattern prevailed during the morning hours across Puerto Rico and the U.S. Virgin Islands, with limited cloud cover and shower activity observed across the region. Maximum daytime temperatures ranged from the mid-to-upper 80sF and in the upper 70s to lower 80s across the mountains, resulting in warm conditions across the local islands, particularly along the coastal and urban areas of Puerto Rico.

A wetter and more active weather pattern is expected across Puerto Rico and the U.S. Virgin Islands as tropical moisture gradually spreads across the region. Model guidance suggests precipitable water values increasing to around 2.2 to 2.3 inches, well above climatological normals, while an upper-level trough will provide additional support for shower and thunderstorm development. At the surface, a high-pressure system over the central Atlantic will maintain a southeasterly wind flow across the region, generally gentle to moderate, with locally fresh winds possible across the Caribbean waters and southern coastal areas. Under this pattern, increasing cloudiness may somewhat limit daytime heating; however, the combination of abundant tropical moisture, local effects, and sea-breeze convergence will favor scattered to numerous showers and thunderstorms, particularly across northwestern Puerto Rico during the afternoon hours, with some activity potentially extending into the early evening. The main hazards associated with the strongest showers and thunderstorms will be frequent lightning and periods of locally heavy rainfall, which may result in minor urban and small- stream flooding, particularly across low-lying and poor-drainage areas.

A similar weather pattern is expected to persist across the region, although some improvement in upper-level conditions is anticipated as suggested by increasing 250 mb heights. Nevertheless, relatively cold temperatures at 500 mb, ranging between -7C and -6C, along with elevated relative humidity values between 850 and 500 mb, generally near the 75th climatological percentile, will continue to support an environment favorable for shower and thunderstorm development. Additionally, upper-level cloudiness may limit daytime heating, although sufficient moisture and local effects will continue to support afternoon convection. At the surface, the high- pressure system over the central Atlantic will gradually expand toward the Caribbean, promoting a slight shift in the prevailing winds toward the east-southeast. This wind pattern will favor passing showers across windward sections during the morning hours, followed by additional shower and thunderstorm development across northwestern Puerto Rico during the afternoon. Locally heavy rainfall and lightning will remain the primary hazards, with minor flooding possible across urban, low-lying, and poor-drainage areas.

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

(18Z TAFS) Issued at 159 PM AST Wed Oct 21 2026

Mainly VFR conds expected across PR and USVI terminals thru the evening, with only ISOLD SHRA, mainly at TJBQ. VFR conds prevailing overnight. Increasing moisture will favor more frequent SHRA/VCTS across terminals aft 22/17Z, with PROB30 TSRA and MVFR/IFR conds at TJBQ aft 22/21Z. Sfc winds mainly S-SE at 5-12 kt, bcmg L/V overnight, then 10-14 kt with sea-breeze variations.

MARINE

Issued at 159 PM AST Wed Oct 21 2026

Light to gentle south-southeasterly to southeasterly winds will increase to moderate to locally fresh during the weekend and persist through at least early next week, resulting in choppy seas. The current northerly swell will continue to subside, allowing seas to gradually improve. However, another north-northwesterly swell will arrive by early Friday, followed by additional pulses through the weekend. Although seas are expected to remain below Small Craft Advisory criteria, conditions may require small craft to exercise caution, particularly across the Atlantic waters and Mona Passage. Increasing tropical moisture will also favor more frequent showers and thunderstorms from Thursday through the weekend across the Caribbean and Atlantic waters and Mona Passage, with lightning, gusty winds, and reduced visibility.

BEACH FORECAST

Issued at 159 PM AST Wed Oct 21 2026

A High Risk of Rip Currents remains in effect through this evening for north-facing beaches of Puerto Rico, Culebra, St. Thomas, and St. John. Conditions should briefly improve as the current northerly swell subsides. However, another north-northwesterly swell arriving by early Friday, followed by additional pulses through the weekend, will likely bring a renewed High Risk of Rip Currents to northwestern and northern exposed beaches, with some potential for high surf conditions requiring an advisory. Additionally, a wetter pattern from Thursday through the weekend will increase shower and thunderstorm activity near coastal areas, resulting in a greater lightning risk for beachgoers.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk until 6 PM AST this evening for PRZ001-002- 005-008-010-012.

VI...High Rip Current Risk until 6 PM AST this evening for VIZ001.

AM...None.