AFDSJU Area Forecast Discussion National Weather Service San Juan PR 110 PM AST Thu Oct 16 2025 .KEY MESSAGES... * For Puerto Rico, there is a limited to elevated flood threat, with the heaviest showers expected along the eastern sections through Saturday. Another band of thunderstorms from the Atlantic waters could move tonight from the northwest to northeast coast. * For the U.S. Virgin Islands, shower and thunderstorm activity is expected to increase from Friday through Saturday. * A gradual improvement in weather conditions is forecast by late Monday as a drier airmass moves across the islands. * Northerly swells will lead to deteriorating seas and life- threatening rip currents from Friday into early next week. Small craft advisories, rip current/high surf/coastal flood statements will be required, particularly from Sunday through Tuesday. && .SHORT TERM...Rest of today through Saturday... Mostly sunny to partly cloudy skies were observed during the morning hours across the islands after a rainy early morning across Puerto Rico. As of 1 PM AST, high temperatures were from the upper 80s to low 90s across most coastal areas with heat indices up to 105F in general. The wind was from the west to southwest between 6 to 14 mph. A frontal system over the Atlantic waters will linger over the local area through the short-term period. This will promote normal to above-normal precipitable water content between 1.80-2.20 inches. Meanwhile, a polar trough will also promote colder than normal 500 mb temperatures of near -8C, which will support thunderstorm development each day. The flood threat will remain elevated mainly for portions of the Cordillera and the eastern half of PR. However, another band of showers and thunderstorms could move once again from the northwest to northeast coast of PR tonight, leading to brief periods of heavy rainfall and strong gusty winds. Across the USVI, the wettest period is expected from late Friday into Saturday morning. .LONG TERM...Sunday through Wednesday... /From prev discussion issued at 532 AM AST Thu Oct 16 2025 Wet and unstable weather conditions are expected to persist through at least Monday as the remnants of a frontal boundary and its associated moisture continue to influence the local area. This pattern will result in increased moisture and instability, supporting periods of showers and thunderstorm activity across the region. The latest model guidance indicates deep-layer moisture extending from the surface to the mid-levels, maintaining a moist environment favorable for convection. As a result, frequent showers and thunderstorms are expected, with activity affecting mainly the windward and coastal sections during the nighttime and early morning hours, and developing across the interior and western portions of Puerto Rico during the afternoon hours. Given the abundant moisture and instability, lightning and localized flooding threats will range from limited to elevated, particularly across portions of Puerto Rico through Monday. By late Monday, a gradual improvement in weather conditions is expected as drier air filters into the region. For Tuesday and Wednesday, weather conditions should become more stable overall, with moisture levels fluctuating around seasonal to below values for this time of the year. Despite the drying trend, residual moisture and local effects combined with daytime heating will still promote isolated to scattered afternoon showers, mainly over the interior and western Puerto Rico. The flooding threat during this period should remain limited to none. However, by the later part of the workweek, model guidance shows a gradual increase in moisture and shower activity as a tropical wave or potential tropical system moves south of the region. Until then, fair weather and limited convection are expected, with isolated afternoon showers possible over the western interior due to local and diurnal effects. We urge citizens and visitors to continue to monitor the forecast for any significant changes. && .AVIATION... (18Z TAFS) TEMPO MVFR conds possible at TJSJ/TIST/TISX thru 16/23z due to SHRA/TSRA. A lingering frontal system over the Atlantic waters will continue to produce strong thunderstorms over the local waters, and under westerly steering winds this can lead to intermittent periods of SHRA/TSRA once again tonight at TJBQ/TJSJ. The 16/12z TJSJ sounding indicated WSW winds at 8-14 kt blo kt blo 3000ft. && .MARINE... A frontal system over the Atlantic offshore waters will continue to produce showers and thunderstorms across the regional waters through the weekend. Light southwesterly winds are expected during this period. Pulses of a long period northerly swell will reach the Atlantic waters and passages from Friday into early next week. Hazardous seas building up to 8 feet are expected from late Sunday into Monday, triggering Small Craft Advisory conditions across the Atlantic waters and Caribbean Passages through midweek. Moderate to locally fresh easterly winds will return from Sunday onward. && .BEACH FORECAST... Pulses of long period northerly swells will gradually increase the threat of life-threatening rip currents along the west, north, and eastern beaches of the islands during the next few days. High surf conditions and minor coastal flooding are likely on Sunday and Monday as the northerly swell builds seas between 6 and 8 feet around 12 to 14 seconds, which translates to breaking waves between 10 and 15 feet. Dangerous swimming conditions, minor beach erosion, and life-threatening rip currents are expected from this weekend into early next week. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$