AFDSJU Area Forecast Discussion National Weather Service San Juan PR 505 AM AST Fri Dec 19 2025 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 500 AM AST Fri Dec 19 2025 * Life-threatening rip currents will prevail across the northern exposed beaches of Puerto Rico and Culebra through this afternoon. Moderate risk across the U.S. Virgin Islands. * Another northerly swell and increasing trade winds will cause hazardous seas and life-threatening rip currents to redevelop from Saturday afternoon through Sunday. * Isolated showers this morning across windward portion of Puerto Rico and the U.S. Virgin Islands, then drier air will limit rainfall and promote stable conditions most of the day, with localized afternoon showers developing across western Puerto Rico. * Cooler temperatures and better rain chances are anticipated around mid-week next week due to an approaching frontal boundary and better dynamics aloft. && .Short Term(Today through Sunday)... Issued at 500 AM AST Fri Dec 19 2025 A surge of moisture brought scattered to widespread passing showers across the local waters, the US Virgin Islands, and the windward locations in Puerto Rico. This activity results in periods of moderate to locally heavy rain. Meanwhile, the leeward portions of PR had calm weather conditions, with mostly clear to partly cloudy skies overnight. Most of the activity moved out of the USVI region around 2 AM AST, leaving mostly clear skies early this morning. The winds were mainly from the northeast, influenced by land breeze variations. Minimum temperatures ranged from the low to mid-70s along the coast to the low-60s in the mountains and valleys. As the overnight surge of moisture exits the region, there is a high likelihood (70-80%) that a drier air mass will advect into the islands from the east. This drier air, interacting with a mid- to upper-level ridge aloft, will very likely (>70%) suppress deep convection and limit rainfall coverage across Puerto Rico and the U.S. Virgin Islands through at least Saturday. Overall, a stable weather pattern is likely to persist (60-80%) through Saturday. By Sunday, model guidance indicates a moderate to slightly high confidence (50-60%) that the mid-level ridge will weaken, allowing moisture to increase into the mid-levels and marginally enhance atmospheric instability across the region. Under this pattern, the probability of rainfall today and Saturday will generally range from low (0-20%) to moderate (30-50%). With east-northeasterly winds persisting, the highest likelihood of passing showers will remain over windward areas of Puerto Rico and the U.S. Virgin Islands during the early morning and evening hours, while interior and western Puerto Rico will have a low to moderate chance (20-40%) of afternoon showers driven by local and sea-breeze effects. From late Saturday night into early Sunday morning, the probability of rainfall is expected to increase from moderate (30-50%) to high (60-70%), as weakening ridging aloft and a surface-level perturbation enhance low- to mid-level moisture availability. As a result, the flooding risk is likely to increase from none to limited during this period. Under a limited risk scenario, frequent periods of moderate to locally heavy rainfall could lead to ponding of water on roads and in poorly drained areas, with a low probability of isolated urban and small-stream flooding. && .Long Term(Monday through Friday)... Issued at 500 AM AST Fri Dec 19 2025 Early next week, mid level ridging will gradually weaken as a polar trough exiting the eastern United States advances from the northwest. Surface high pressure building across the western Atlantic will promote persistent northeast flow across the region while a frontal boundary is pushed into the central Atlantic. Patches of low level moisture will continue to move across the area, resulting in isolated to scattered showers over windward sections of Puerto Rico and the U.S. Virgin Islands, mainly during the night and morning hours. By late morning into the afternoon, a moderate chance of scattered showers, around 50 percent, is expected across interior and western Puerto Rico, posing a limited flood risk on Monday and Tuesday. From Tuesday onward, atmospheric instability will increase as 500 mb temperatures cool to below normal values between -7 and -10 degrees Celsius. Rain chances will increase, with probabilities rising to 50 to 60 percent for scattered to numerous showers.A polar trough will extend southward into the Caribbean, while an additional upper-level trough will interact with a surface frontal boundary across the region. The frontal boundary will linger close to the area, allowing moisture to pool across the region, while enhanced upper-level divergence and atmospheric instability will support rising motion. As a result, unsettled weather conditions will develop,, particularly from Wednesday through Friday, with increasing cloudiness, showers, and isolated thunderstorms expected across parts of the Caribbean. As the frontal boundary approaches and lingers to the north of the region, precipitable water values will increase to between 1.5 and 1.8 inches, within the seasonal to above normal range. Model guidance, including the Galvez Davison Index, supports the potential for shallow convection with isolated thunderstorm development. Periods of locally heavy rainfall may lead to localized flooding in flood prone and poorly drained areas, including roadway ponding. At this time, flood risk ranges from limited to elevated for portions of Puerto Rico, particularly across the northeastern sectors. Cooler temperatures are expected during the holiday period, as indicated by a trend toward below normal 925 mb temperatures. && .AVIATION... (06Z TAFS) Issued at 500 AM AST Fri Dec 19 2025 VFR conditions will prevail through much of the forecast period, without ruling out a few passing showers near or across JSJ/IST/ISX. SHRA/-SHRA will then form over the interior and western PR (near JBQ) between 19/17-23z. Winds will be calm to light and variable through this morning, then return from the ENE after 19/13z at 10- 15kt with higher gusts and sea breeze variations. && .MARINE... Issued at 500 AM AST Fri Dec 19 2025 Moderate to locally fresh east to northeast winds will continue across the local waters today. A Small Craft Advisory (SCA) remains in effect through midday today for the offshore Atlantic waters, due to hazardous marine conditions for small craft operators. Seas are expected to briefly subside this afternoon through early Saturday. However, another long-period northerly swell, generated by a surface low over the central Atlantic, will spread across the local Atlantic waters and Caribbean passages, causing hazardous marine conditions to redevelop and SCA conditions to return Saturday afternoon into Sunday. && .BEACH FORECAST... Issued at 500 AM AST Fri Dec 19 2025 A High Risk of rip currents continues through this afternoon along the north-facing beaches of Puerto Rico and Culebra. Dangerous rip currents are likely within the surf zone, and beachgoers are urged to strictly follow guidance from lifeguards, beach patrol flags, and posted signs. Tonight, the risk is expected to decrease to moderate for most beaches through Saturday night, while low risk conditions will prevail along the southern beaches of the islands. Remember, a moderate risk means that life-threatening rip currents are possible, and even during low risk conditions, dangerous rip currents can still occur, especially near groins, jetties, reefs, and piers. By late Saturday into Sunday, beach conditions are forecast to deteriorate again as strengthening winds and another northerly swell spread across the local Atlantic waters, leading to large breaking waves. Stay tuned to the forecast and exercise caution at the beaches. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through this afternoon for PRZ001-002-005- 008-012. VI...None. AM...Small Craft Advisory until noon AST today for AMZ711. Small Craft Advisory from noon Saturday to noon AST Sunday for AMZ711. && $$