textproduct: San Juan

KEY MESSAGES

Issued at 133 PM AST Wed Dec 10 2025

* Marine and beach conditions will deteriorate beginning Thursday. Expect choppy to rough seas and life-threatening rip currents.

* Breezy to windy conditions are anticipated today across coastal and elevated areas. Light-weight outdoor items may be blown around in exposed locations.

* For Puerto Rico, shower activity will increase throughout the day, with limited flooding risk over eastern portions during the morning and the northwestern section in the afternoon.

* For the U.S. Virgin Islands, showers will become more frequent today, promoting ponding of water over roadways and poorly drained areas.

Short Term(This evening through Friday)

Issued at 133 PM AST Wed Dec 10 2025

The latest radar and satellite imagery reveal ongoing light to moderate showers and associated cloud cover translating east in response to a trade wind perturbation. Overall rainfall amounts are expected to remain light as the highest moisture content remains further east, but pockets of brief, locally heavy rainfall cannot be ruled out, especially as the aforementioned perturbation interacts with diurnal instability and the local sea breeze. This may result in ponding of water on roadways or low- lying, flood-prone areas. Otherwise, expect occasional wind gusts around 20-25 MPH through the afternoon hours and early evening hours, mainly across the east-facing coast and eastern islands. These gusts should begin to subside later this evening and overnight over Puerto Rico, generally below 10 MPH.

Through the end of the week, similar conditions are expected as fluctuations in precipitable water values, diurnal instability, and the influence of the local sea breeze allow for isolated to scattered showers through Friday. No significant flooding threat is expected as rainfall amounts should remain light give the shallow nature of the moisture content in the lower levels. Easterly to southeasterly winds should remain fairly light, generally around or below 10 MPH over Puerto Rico, with elevated winds over the waters and eastern islands.

LONG TERM(Saturday through Wednesday)

Issued at 133 PM AST Wed Dec 10 2025

Variable conditions may persist early next week, introducing changes to the long-term forecast. The surface high pressure lingering over the Central Atlantic will continue to promote southeasterly winds, bringing breezy to windy conditions on Saturday. Due to the presence of the mid-level ridge lingering northeast of the region, shower activity should remain limited. But conditions will slightly worsen as a disturbance in the trades is now expected to arrive late Saturday night into Sunday, increasing the frequency of showers across the windward sections of the islands. From the latest probabilistic guidance of the GFS and the ECMWF, ensemble members are now tending to a wetter pattern for this time of the year, as there is a medium chance of seasonal and above climatological normal Precipitable Water (PWAT) values (1.4 - 1.6 inches), with a low chance of reaching 2.0 inches. By late Sunday night, the moisture content should decrease and remain between 1.2 and 1.4 inches. Although the frequency of showers should decrease, the latest guidance suggests that the surface high pressure will interact with a polar trough, weakening the pressure gradient. Winds should become light and variable by Monday and Tuesday, meaning any developing shower will likely become stationary and produce higher rainfall accumulations. The latest model solutions show the polar trough deepening more into the tropics, cooling 500 mb temperatures (around -7 degrees Celsius), and enhancing marginal instability conditions. Additionally, an upper level trough may weaken the mid-level ridge and increase instability aloft. Although the lightning risk is not expected to be widespread, the chance of short-lived isolated thunderstorms is increasing. Overall, afternoon convection is expected each day of the period, with flooding potential increasing on Monday and Tuesday, particularly over portions of western/northwestern Puerto Rico and the San Juan Metropolitan Area. Although the flooding risk is not anticipated across the U.S. Virgin Islands, streamers developing near noon may linger near the coastal areas.

With southeasterly winds expected through most of the period, warmer than normal temperatures will continue across the islands, with very localized areas reaching 100 degrees Fahrenheit heat indexes during daytime. Nevertheless, no heat risk is expected across the islands for the rest of the forecast period.

AVIATION

(18Z TAFS) Issued at 133 PM AST Wed Dec 10 2025

Periods of SHRA/VCSH will continue through the early evening hours in response to a trade wind perturbation that is translating across the region. Brief periods of MVFR ceilings and visibility cannot be ruled out within any robust showers. Expect easterly to southeasterly winds around 10-15 knots, with occasional higher gusts through the afternoon hours. Winds will fall below 10 knots overnight at TJBQ, TJPS, and TJSJ, but will remain elevated at TIST and TISX.

MARINE

Issued at 133 PM AST Wed Dec 10 2025

A building surface high pressure over the Central Atlantic will continue to promote easterly gentle to moderate winds today, becoming moderate to locally fresh tonight. Increasing winds combined with a long- period northerly swell arriving early Thursday will lead to choppy to rough seas mainly over the Atlantic offshore waters. A Small Craft Advisory in effect from Thursday morning through late Thursday night. Although conditions will slightly improve by Friday, hazardous conditions for small craft may return by the weekend.

BEACH FORECAST

Issued at 133 PM AST Wed Dec 10 2025

Today, the rip current risk will remain moderate along the north and east-facing beach of Puerto Rico, including Vieques and Culebra, and the U.S. Virgin Islands. Although the risk is moderate, beachgoers are encouraged to exercise caution as life- threatening rip current are possible along the surf zone.

The forecast remains on track, as increasing winds combined with a northerly long- period swell arriving early tomorrow will increase breaking wave along exposed beaches and bring hazardous beach conditions. Hence, a high risk of rip currents is anticipated along the northern beaches of Puerto Rico and the U.S. Virgin Islands. As the swell spreads and diminishes by Friday, dangerous beach conditions may persist in the weekend. Residents and visitors are are urged to check the beach forecast before going out, and heed the advice of the flag warning system.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...Small Craft Advisory from 6 AM Thursday to 6 AM AST Friday for AMZ711.