textproduct: San Juan

KEY MESSAGES

Issued at 128 PM AST Fri Oct 31 2025

* Heavy showers and thunderstorms due to the passage of a tropical wave will persist through the evening hours. This will result in a limited to elevated flooding risk mostly across portions of western/northwestern Puerto Rico. Frequent lightning and gusty wind conditions can be expected with the strongest thunderstorms.

* The tropical wave will linger through Saturday,bringing periods of moderate to heavy rain with isolated thunderstorms.

* For the U.S. Virgin Islands, expect periods of passing showers particularly during the morning hours this weekend.

* A moderate rip current risk will continue through early next week across the north-facing beaches in Puerto Rico and the U.S. Virgin Islands.

SHORT TERM (This evening through Sunday)

Issued at 128 PM AST Fri Oct 31 2025

Overall, today began with tranquil weather conditions across the region, with some pockets of showers over the surrounding waters. This was followed by an active afternoon as showers and thunderstorms developed across the interior and western portions of Puerto Rico. Earlier, isolated showers affected the U.S. Virgin Islands and eastern Puerto Rico, resulting in minimal accumulations. The calm weather and clear skies in the morning allowed temperatures to reach the upper 80s to low 90s, with heat indices increasing into the 100s during the afternoon hours.

Tonight into Saturday, a slightly unsettled pattern with frequent showers will persist as abundant tropical moisture associated with a tropical wave moves mainly south of Puerto Rico and the U.S. Virgin Islands. Precipitable water (PW) values are increasing from around 1.80 inches to near 2.00 inches tonight, supporting higher moisture content across the region. On Saturday, PW values between 2.0 and 2.50 inches, combined with 500-mb temperatures near -7C, will promote an unstable atmosphere. These conditions will favor the vertical development of showers and thunderstorms, leading to another active afternoon across the interior and western municipalities of Puerto Rico, as well as downwind of the local islands and El Yunque. Activity will favor windward and eastern areas overnight into early Saturday morning. As a result, there will be an elevated risk of flooding and a limited risk of lightning through late Saturday.

A significant change in weather conditions is expected on Sunday as a much drier air mass filters into the region from the east. Precipitable water values are forecast to drop to near or below the 25th percentile for this time of year, leading to a noticeable decrease in shower activity. Mostly fair weather is anticipated, with only brief, light showers possible in windward areas.

LONG TERM (Monday through next Thursday)

Issued at 335 AM AST Fri Oct 31 2025

The first half of the long-term period will be influenced by an upper-level low-pressure system moving south of the area, over the Caribbean waters. This will lead to a weakening of atmospheric stability across the region. In combination with sufficient low- level moisture, this pattern will help promote showers across the area from Monday through at least Tuesday.

Despite the upper-level low, a strong mid-level ridge is expected to persist through the entire period, promoting stable and relatively drier conditions aloft. At the surface, a strong high-pressure system over the central Atlantic is forecast to tighten the pressure gradient, resulting in breezy easterly winds through late Tuesday. Winds will then shift from the southeast from Wednesday onward.

Under this pattern, patches of low-level moisture will continue to filter into Puerto Rico and the U.S. Virgin Islands. This will bring a low to medium chance (20 to 40%) of occasional passing showers over the windward portions of the U.S. Virgin Islands and eastern Puerto Rico during the morning hours. Later in the afternoon, shower activity is likely over portions of western and northwestern Puerto Rico due to local orographic effects, sea-breeze interactions, and diurnal heating. A few isolated thunderstorms are possible and cannot be ruled out.

Limited to elevated heat conditions are expected next week, driven by normal to above-normal temperatures at the 925 mb level. Maximum temperatures along the coastal and urban areas are forecast to range from the mid to upper 80s, and in the mountain areas, highs are expected to be in the upper 70s to low 80s.

AVIATION

(18Z TAFS) Issued at 128 PM AST Fri Oct 31 2025

Most TAF site shld experience mainly VFR conds. However, MVFR conds possible with the afternoon convective dvlpmnt. VCTS and SHRA possible across TJBQ and TJPS expected through 31/22Z. After 31/23Z showers are possible across the TISX, TIST, TJSJ, and TJBQ along with VCTS possible as a tropical wave moves south of the area. SFC WNDS E-SE 5 to 10KT occasional higher gust.

MARINE

Issued at 128 PM AST Fri Oct 31 2025

A surface high pressure over the Central Atlantic and a tropical wave moving across the eastern Caribbean will promote moderate to locally fresh trade winds this weekend. Additionally, thunderstorm activity is expected across the local waters and passages as the tropical wave moves across the region.

BEACH FORECAST

Issued at 128 PM AST Fri Oct 31 2025

Beachgoers can expect a moderate risk of rip currents along the north and east-facing beaches in PR and the USVI. The moderate risk will persist this weekend into early next week. Over the weekend, the moderate risk will expand to most local beaches as winds strengthen ahead of an approaching tropical wave. Additionally, the potential for thunderstorms will increase on Saturday due to the arrival of a tropical wave. Beachgoers should remain cautious and follow guidance from local authorities and lifeguards.

SJU WATCHES/WARNINGS/ADVISORIES

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