AFDSJU Area Forecast Discussion National Weather Service San Juan PR 518 AM AST Fri Dec 12 2025 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 409 AM AST Fri Dec 12 2025 * Choppy to rough seas and life-threatening rip currents are expected to continue through the weekend. * For Puerto Rico, passing showers are expected mainly during the night/early morning hours across coastal areas of eastern, southern, and northern PR, followed by afternoon shower activity over the western PR. * For the U.S. Virgin Islands, fair weather conditions expected through the morning hours. Passing showers increasing once again later tonight through Saturday. && .Short Term(Today through Sunday)... Issued at 409 AM AST Fri Dec 12 2025 Isolated to scattered showers associated with a disturbance persisted during the night, moving across the local waters and portions of southern and eastern Puerto Rico, as well as the U.S. Virgin Islands. Based on the WSR-88D rainfall estimates, these areas received up to 1 inch of precipitation. By midnight, isolated thunderstorms developed over the Mona Passage, producing lightning. Temperatures were slightly warmer than yesterday, as cloud cover inhibited effective radiative cooling, and stations reported less widespread cooler temperatures. Over coastal areas, temperatures remain in the mid-70s, while higher elevations stayed in the mid to high 60s, with isolated areas dropping to the low 60s. Stronger winds were seen last night, as more stations in coastal areas and higher elevations reported wind gusts up to 27 mph. Small changes were introduced to the short-term forecast, as variable conditions are likely to persist in the weekend. As the disturbance continues to retreat from the region, satellite-derived products show the drier air mass mentioned in the previous discussion already started filtering into the region, bringing mostly fair conditions across the CWA. Based on the latest model solutions, low to mid level moisture content should plummet to below climatological normal ( with PWAT values between 1.0 and 1.2 inches, even lower), which should limit the shower activity for today. The surface high pressure will strengthen and linger over the Central Atlantic throughout the period, with east-southeasterly winds increasing, leading to breezy to windy conditions across the islands. The mid-level ridge northeast of the region is now expected to weaken due to a polar trough deepening into the tropics, which will slightly cool 500 mb temperatures (between -6 and -7 degrees Celsius), promote cloud growth, and introduce marginal instability across the CWA. Confidence is increasing in the short term, as deterministic guidance of the GFS and ECMWF currently agrees on an increase of moisture content due to a disturbance in the trades moving across the region tonight, and another on Saturday evening into early Sunday. Ensemble members are now tending to a wetter pattern for this time of the year, with PWAT values likely between 1.4 and 1.6 inches, a medium to high chance of reaching 1.8 inches on Saturday night (above climatological normal). The most likely scenario remains, with an increase in shower activity, particularly across the U.S. Virgin Islands and the eastern half of Puerto Rico, becoming stronger on Saturday evening. Although showers and isolatd thunderstorms will likely be progressive rather than stationary, periods of heavy showers will likely lead to ponding of water along roads and poorly drained areas, with isolated urban and small streams flooding. Hence, the flooding risk will remain limited, particularly over northeastern Puerto Rico, including Vieques and Culebra, and St. Thomas and St. John in the U.S. Virgin Islands. Weather conditions should improve by Sunday morning, as another drier air mass will reduce moisture content in the low and mid levels, enhancing stability across the CWA and limiting shower activity. As mentioned in the previous discussion, a southeasterly wind pattern will continue pooling warmer air, leading to above climatological normal temperatures in the short term. Nevertheless, the heat threat will remain low for the rest of the period. && .Long Term(Monday through Friday)... Issued at 409 AM AST Fri Dec 12 2025 Global models have a wetter solution than previous days with the approaching frontal system over the western Atlantic and associated upper level trough promoting more unstable conditions through first part of the workweek. The 500 mb temperatures are expected to drop to around -6.5C and the precipitable water content is expected to remain near 1.75 inches, above normal levels for most of the period. The mid-to upper-level ridge is now expected to erode earlier and have little influence in the local weather conditions. Pooling of normal to above normal moisture content over the area will lead to weak surface troughs to move from the east on most days, increasing the chance of showers between 50-70% each day across the islands, with a slight chance of thunderstorm development over western PR in the afternoon hours. However, decided to not include them in the forecast as of now due to possible model variations. At the surface, a broad high pressure will linger near and south of the Azores through the long term period. Meanwhile, a cold front over the western Atlantic should remain north of the region early in the forecast. This will promote a southeasterly wind flow, leading to warmer than normal temperatures before the onset of afternoon showers. Another surface high pressure is expected to build behind the front and over the western Atlantic during the second part of the week, bringing east to northeast trades and a cooler air mass. && .AVIATION... (06Z TAFS) Issued at 409 AM AST Fri Dec 12 2025 Mainly VFR conds are expcd across most TAF sites, with VCSH due SHRA associated to disturbance through at least 12/12z. Winds from the E- SE will increase by 12/13-14z, around 15 kt with gusts up to 25 kt through 12/23z. VFR conds will return in the morning as a drier ams will move across the CWA, reducing SHRA activity, returning after 12/22-23z. VCSH for most terminals, that may reduce CIGs/VIS and lead to brf MVFR conds. && .MARINE... Issued at 409 AM AST Fri Dec 12 2025 A surface high pressure will continue to build near the Azores through the weekend. A weak cold front and another surface high pressure will move from the western Atlantic into the central Atlantic during the next few days. This will promote moderate to locally fresh east to southeast trades across the local waters. Increasing winds and a long period northerly swell will cause choppy to rough seas, mostly across the Atlantic waters and portions of the Anegada and Mona Passages. && .BEACH FORECAST... Issued at 409 AM AST Fri Dec 12 2025 A long period northerly swell and increasing wind-waves will cause life-threatening rip currents along the north and east facing beaches of the islands during the next few days. There is a Rip Current Statement in effect for the northwest to northeast beaches of PR, including Culebra, and the northern USVI. Beach goers are urged to avoid swimming in these conditions, particularly today and on Friday. The west/southern beaches of the islands will have a moderate risk of rip currents. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Saturday afternoon for PRZ001-002- 005-008. High Rip Current Risk through late tonight for PRZ012. VI...High Rip Current Risk through late tonight for VIZ001. AM...Small Craft Advisory until 5 PM AST Sunday for AMZ711. Small Craft Advisory until 6 PM AST this evening for AMZ712-716. Small Craft Advisory until noon AST Saturday for AMZ723. Small Craft Advisory until midnight AST tonight for AMZ741. && $$