AFDSJU Area Forecast Discussion National Weather Service San Juan PR 405 AM AST Tue Dec 30 2025 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 401 AM AST Tue Dec 30 2025 * Hazardous coastal conditions will persist across the northern coastal areas of Puerto Rico, Culebra, and St. Thomas, where a high risk of rip currents remains in effect. * Easterly wind flow will return today; therefore, more seasonable temperatures are expected today and tonight. * Puerto Rico and the U.S. Virgin Islands: For tomorrow, the last day of 2025, a more unsettled weather pattern is forecast with the arrival of moisture from a frontal boundary and added instability from an upper-level trough. && .Short Term(Today through Thursday)... Issued at 401 AM AST Tue Dec 30 2025 Skies will remain mostly clear to partly cloudy today across much of the forecast area, as the overall pattern remains similar to the past several days. Ridging aloft with dry mid-levels will continue to promote relatively stable weather conditions. At the surface, high pressure over the central Atlantic will continue to shift eastward, resulting in winds veering from east-northeast to a more southeasterly component, remaining mostly light to moderate. These southeasterly winds will persist across the region through the short- term forecast period. Only isolated brief showers are expected, mainly over windward coastal areas during the morning hours and across the western interior of Puerto Rico during the afternoon due to local effects, as well as over the surrounding waters at times. Temperatures will remain slightly below normal, resulting in pleasant conditions across the islands once again. From Wednesday into Thursday, weather conditions will become more variable as a deepening polar trough moves over the region, enhancing dynamics aloft. Model guidance continues to indicate falling mid-level heights and 500 mb temperatures dropping to around -9 to -10 C. This will result in steeper low- to mid-level lapse rates and a more favorable environment for convective development. At lower levels, a surge of tropical moisture is expected to arrive, with precipitable water values increasing to near 1.8 to 2.0 inches and 700-500 mb relative humidity values rising well above 2 standard deviations above climatological normals. Despite the increasingly favorable dynamic setup, guidance remains consistent in keeping the highest moisture content and more organized convective activity focused west of the local islands, particularly over Hispaniola and the Mona Passage. As a result, shower and thunderstorm coverage over Puerto Rico and the U.S. Virgin Islands may not be as widespread, with much of the activity favoring the waters west and northwest of Puerto Rico. Still, periods of shower activity are expected across the area. Afternoon convection will be possible over the western and interior sections of Puerto Rico, particularly on Thursday, driven by the combination of favorable dynamics aloft, diurnal heating, and local effects. Additionally, nighttime and early morning trade wind showers, along with isolated thunderstorms developing over the regional waters, could affect coastal areas, particularly along the western half of the CWA. Brief heavy rainfall, gusty winds, and isolated lightning strikes will be possible with stronger thunderstorms, although widespread activity is not anticipated. Overall, the short-term period will feature a transition from todays relatively stable and pleasant conditions toward a more unsettled pattern by mid to late week, with increasing moisture and enhanced instability aloft, while the highest impacts are expected to remain mainly over the surrounding waters. && .Long Term(Friday through Tuesday)... Issued at 401 AM AST Tue Dec 30 2025 An unstable weather pattern will persist on the first day of the long term, as the main weather pattern is dominated by a mid- to upper-level trough. This upper-to mid-level feature will create a very unstable weather pattern, enhancing colder temperatures at 500 MB, ranging from -8 to 9 degrees. Meanwhile, at the surface, moisture from a sinking frontal boundary over the Caribbean and instability from the pre-frontal trough will align perfectly with the upper instability, increasing the frequency and coverage of showers during the day. Given the variability of winds due to weakening of the pressure gradient resulting from the surface pre- frontal trough, the coverage and movement of showers will be slow and widespread across the mountain sections. Upper conditions will rapidly improve as the subsidence side of the upper-level trough moves eastward, and a more stable condition will dominate. At 500 MB, a ridge will move in, warming temperatures from -9 to -5 degrees. Stable conditions will persist from Saturday into Monday; however, at the surface, shallow patches of moisture dragged by the east-southeasterly wind flow will allow some showers in the morning across the eastern side and across the interior and western Puerto Rico for the afternoon. There are some discrepancies in the amount of available moisture (relative humidity %) on those days, with the ECMWF calling for a wetter, more seasonal pattern. On Tuesday again, weather conditions will deteriorate as another upper-level trough moves into the Caribbean. Combined with the instability, values of Relative humidity between 700 and 300 MB show an increase in moisture, which will induce a more showery pattern. && .AVIATION... (06Z TAFS) Issued at 401 AM AST Tue Dec 30 2025 Mainly VFR conds exp across all TAF sites thru the fcst pd. Brief - SHRA/VCSH psbl at times, mainly at TJSJ/TIST/TISX, with SCT-BKN cigs btw FL030FL060 at times. Any VIS/CIG reductions expected to be brief. Winds lgt/vrb ovrngt, bcmg ESESE at 812 kt aft 14Z, then diminishing again aft 23Z. && .MARINE... Issued at 401 AM AST Tue Dec 30 2025 A surface high pressure system moving eastward from the western into the central Atlantic, interacting with the remnants of an old frontal boundary, will maintain a light easterly wind flow across the region through Tuesday. From late Wednesday into Friday, an approaching frontal boundary combined with a strengthening high- pressure system over the central Atlantic will result in a moderate east-to-east-southeast wind flow, increasing the potential for showers and isolated thunderstorms and enhancing localized hazardous marine conditions. During the period, pulses of long-period northerly swell will continue to propagate across the Atlantic waters and Caribbean passages through the middle of the week. Small craft operators are urged to exercise caution, particularly across the exposed Atlantic waters and Caribbean passages. && .BEACH FORECAST... Issued at 401 AM AST Tue Dec 30 2025 A long-period northerly swell will continue to propagate across the northern regional waters, resulting in a persistent high risk of dangerous rip currents along north-facing beaches of Puerto Rico, Culebra, St. Thomas, and St. John. Therefore, a Rip Current Statement will remain in effect through at least Tuesday afternoon. Recent data from buoy 41043, located about 170 nautical miles north of San Juan, indicate another pulse of northerly swell arriving across the islands, with wave heights up to 6 feet and periods near 13 seconds. This swell energy will maintain breaking waves along the northern coastal areas between 6 and 8 feet, with occasionally higher sets. Given the forecast conditions, a high rip current risk is expected to persist through Thursday, with gradual improvement as the weakening swell dissipates. Nevertheless, even as conditions improve, hazardous rip currents may still develop near groins, jetties, reefs, and piers during periods of lower risk. Beachgoers are advised to exercise caution at all times when entering the water. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Wednesday afternoon for PRZ001-002- 005-008-012. High Rip Current Risk through this afternoon for PRZ010. VI...High Rip Current Risk through late tonight for VIZ001. AM...None. && $$