textproduct: San Juan

KEY MESSAGES

Issued at 218 PM AST Fri Mar 13 2026

* Flooding in urban areas, on roads, and along small streams is possible this afternoon across the interior and western Puerto Rico.

* Mostly sunny conditions are expected on Saturday, although a few localized showers may still develop during the afternoon hours across western Puerto Rico.

* Increasing winds are expected on Sunday into next week, leading to hazardous marine and beach conditions.

* Across the U.S. Virgin Islands, occasional passing trade-wind showers will continue, with a drying trend expected by late tonight into Saturday.

Short Term(This evening through Sunday)

Issued at 218 PM AST Fri Mar 13 2026

The day began with shower activity across the local waters, with some showers reaching eastern areas of Puerto Rico due to a patch of moisture. Based on radar estimates, rainfall accumulations were minimal across most areas, with the highest amounts observed in Naguabo, where totals ranged between 0.50 and 0.75 inches in some locations. Around noon, a streamer developed and produced rainfall amounts between 0.20 and 0.50 inches across parts of the metro area, with localized maximums near 0.60 inches. Temperatures along coastal areas ranged from the low to mid 80s, while interior and mountainous locations remained in the 70s. Maximum wind gusts reached the low to mid 20s mph across coastal areas of Puerto Rico and the U.S. Virgin Islands.

Moving into the afternoon hours, cloudiness has started to increase across the islands. The morning sounding from San Juan (TJSJ) showed precipitable water (PWAT) values of 1.40 inches, while satellite-derived data indicates an area of moisture over the region near 1.5 inches or slightly higher. These values are near seasonal levels to slightly above normal based on climatology for this time of year. This available moisture, combined with daytime heating and local effects, will promote the continuation of afternoon convection across the interior and western portions of Puerto Rico. Periods of moderate rainfall are possible, increasing the potential for ponding of water on roads and in poorly drained or urban areas. The flood risk remains limited, currently at level 2 out of 5 on the graphical hazardous outlook scale.

Looking ahead to tomorrow, it should be the driest and most stable day of the short-term period. A noticeable drying trend will begin late tonight and continue into Saturday. Global guidance indicates a sharp drop in moisture, with precipitable water values falling below 1.25 inches. In addition, mid-level relative humidity (700500 mb) is expected to drop below 20 percent, along with warmer temperatures aloft as a mid-level ridge establishes itself over the region. As a result, expect mostly sunny conditions on Saturday, with only localized and shallow afternoon showers over western Puerto Rico. No flooding risk is anticipated tomorrow.

On Sunday, precipitable water values are expected to increase again to around 1.5 inches (near to slightly above normal levels) as another patch of moisture approaches the region. However, limited instability is anticipated. As a result, an increase in occasional trade-wind showers is expected to affect eastern Puerto Rico and the U.S. Virgin Islands during the overnight and morning hours, followed by isolated afternoon activity across western Puerto Rico. The main weather hazard will be increasing winds. Breezy to windy conditions are expected, so loose objects should be secured as they may be blown around or damaged.

LONG TERM(Monday through Friday)

Issued at 218 AM AST Fri Mar 13 2026

A broad surface high-pressure system over the western Atlantic will strengthen by early next week, tightening the pressure gradient across the northeastern Caribbean and promoting a steady increase in easterly to east-southeasterly low-level flow beginning Monday and persisting through much of the workweek. Model guidance indicates 925 mb winds increasing well above climatological values, peaking near or above two standard deviations above normal on Monday. As a result, breezy to locally windy conditions are expected, particularly across coastal areas of Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands, where a limited to locally elevated wind threat may develop and unsecured outdoor items could be blown around or damaged. Although the pressure gradient is expected to relax slightly after Monday, winds will likely remain above normal through the remainder of the forecast period.

Mid-level conditions will remain generally stable through the forecast period. Model guidance continues to show 700500 mb lapse rates below normal to near the lower end of climatological values, while 500 mb temperatures remain near climatological normals. Although a polar trough and its associated frontal boundary are forecast to move off the eastern seaboard early next week, and an upper-level trough may develop northeast of the forecast area toward the end of the period, the local area will remain largely removed from the strongest dynamical forcing. As a result, most of the region will continue to experience marginally stable conditions, limiting deep convective development and favoring mainly shallow trade wind showers. Relative humidity values in the mid-levels will also remain modest, further supporting a generally stable pattern.

Moisture levels will remain near climatological normals through most of the period, with precipitable water generally fluctuating between around 1.2 and 1.5 inches. Patches of shallow moisture embedded within the trade wind flow will periodically move across the region, resulting in brief passing showers across windward sectors, particularly during the nighttime and morning hours across eastern Puerto Rico and the U.S. Virgin Islands. During the afternoons, diurnal heating combined with local effects may support the development of isolated to scattered showers across interior and western portions of Puerto Rico. However, the faster steering wind flow will limit the residence time of showers and keep rainfall accumulations generally low. Despite this, ponding of water on roads and in poorly drained areas, along with brief reductions in visibility, can still occur in areas experiencing the heaviest showers.

AVIATION

(18Z TAFS) Issued at 218 PM AST Fri Mar 13 2026

Mainly VFR conds across all TAF sites most of the period, except for some intermittent MVFR over the next hours due to VCSH/SHRA moving near TJBQ, VCSH in TJSJ and VCSH/-RA in northern USVI. E-NE winds btwn 10-15 kt with gusts up to 20 kt and sea breeze variations until 13/23Z, then lighter winds overnight.

MARINE

Issued at 218 PM AST Fri Mar 13 2026

A surface high pressure extending over the eastern and central Atlantic will maintain moderate easterly winds across the local waters. Under this pattern, seas will remain up to 5 feet, and between 3 to 4 feet along the nearshore waters. Starting tomorrow, an increase in the pressure gradient will result in a moderate to locally fresh easterly wind flow, which will strengthen by Sunday. This surface change, combined with a diminishing northeasterly swell, will enhance wind-driven seas, resulting in choppy conditions across all exposed local waters from late Sunday into the upcoming workweek. On Monday through midweek, winds will be the main driver of hazardous marine conditions, with seas up to 7 feet and winds up to 20 knots. Small boat operators should stay tuned for further updates in the small craft advisories and statements.

BEACH FORECAST

Issued at 218 PM AST Fri Mar 13 2026

There is a moderate risk of rip currents for the rest of the day across most of the northern exposed beaches of the islands, with a low risk of rip currents along the south coast of Puerto Rico. Similar conditions will persist on Saturday and Sunday across all coastal areas. Residents and visitors are urged to exercise caution in exposed coastal areas not designated for beachgoers, as well as in areas near jetties and rocks. From late Sunday into the upcoming workweek, a surface high pressure system will increase surface winds, making them more moderate to strong, enhancing wind-driven seas and hazardous coastal conditions. Therefore, the risk of rip currents will increase to high by Monday along the entire north coast of Puerto Rico, including the northeastern and northwestern areas, Culebra, and St. Croix. Beachgoers should continue monitoring the forecast for any updates. For additional information, please visit: weather.gov/beach/sju.

FIRE WEATHER

Issued at 218 PM AST Fri Mar 13 2026

The KBDI in Cabo Rojo it is still above the critical fire weather threshold. Before noon, RH values decreased to low the low 50s in Cabo Rojo and some period of gusts up to 20 mph were registered. For the rest of the afternoon, RH values should increase as afternoon convection is expected across western PR, keeping the risk low. At this time an RFD will not be issued, but we encourage partners to continue monitoring conditions in the coming days, particularly tomorrow as a drier airmass is expected to arrive.

SJU WATCHES/WARNINGS/ADVISORIES

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