AFDSJU Area Forecast Discussion National Weather Service San Juan PR 505 AM AST Wed Dec 10 2025 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 440 AM 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(Today through Friday)... Issued at 440 AM AST Wed Dec 10 2025 Satellite imagery and Caribbean radar data overnight indicated the leading edge of a trade wind perturbation moving into the local area. This feature produced brief clusters of showers across the U.S. Virgin Islands and the southeastern coastal areas of Puerto Rico, although rainfall totals generally remained under one-tenth of an inch. The bulk of deeper moisture and shower activity persisted farther east across the Leeward Islands, coinciding with slightly higher Advected Layer Precipitable Water (ALPW) values within the 700-500 mb layer. For today, the mid-level ridge centered northeast of the region will continue to dominate the overall pattern, while weak troughiness lingers to the northwest. Instability aloft remains marginal and characteristic of the season, but a notable increase in low-level moisture will accompany the advancing perturbation. Model guidance continues to support precipitable water values fluctuating near or around 2.0 inches as the disturbance moves across the islands. As a result, expect an uptick in shower frequency, particularly for windward coastal areas during the morning hours, followed by additional afternoon showers developing over the interior and northwestern Puerto Rico due to diurnal heating and local sea breeze convergence. Low-level winds will strengthen and veer slightly southeasterly through the day, with 925 mb wind speeds forecast to reach above- normal levels. Breezy conditions along coastal sectors are therefore likely, with locally higher gusts in showers. A limited flooding threat remains possible, mainly ponding of water on roads and poor- drainage areas where showers persist. For Thursday and Friday, model guidance indicates a broadly similar pattern, with alternating pockets of drier and moister air moving through the trade wind flow. These fluctuations in precipitable water will largely dictate shower coverage from one period to the next. Overall, mid-level relative humidity is expected to remain on the lower side, limiting vertical development and keeping most showers shallow and brief. During the overnight and morning hours each day, patches of increased moisture will support passing showers across windward coastal areas. As drier slots move in, activity will diminish, especially through the mid-day period. Isolated afternoon showers may still form across the interior and western Puerto Rico due to diurnal heating and sea breeze convergence, but rainfall accumulations should remain light given the persistent mid-level dryness. Breezy east-southeasterly winds will continue, particularly along coastal sectors, with no significant flooding threat anticipated. && .Long Term(Saturday through Wednesday)... Issued at 440 AM 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... (06Z TAFS) Issued at 440 AM AST Wed Dec 10 2025 Mainly VFR across all terminals. A trade-wind perturbation will bring periods of -SHRA/VCSH moving in from the E, mainly affecting USVI terminals (TIST/TISX) and occasionally TJSJ through the morning. Brief MVFR CIGS/VIS possible in passing SHRA. Low-level winds ESE-SE 1016 kt, with ocnl higher gusts aft 14Z. Sea-breeze influences after 14Z may trigger SHRA/VCSH over TJBQ and interior PR terminals. && .MARINE... Issued at 440 AM 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 440 AM 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. && $$