AFDSJU Area Forecast Discussion National Weather Service San Juan PR 309 AM AST Sat Mar 21 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 304 AM AST Sat Mar 21 2026 * Today, southerly winds will contribute to above-normal daytime temperatures and limited shower activity, with cloudiness increasing through the afternoon hours. * A more unsettled weather pattern is forecast from late tonight into Sunday, as shower and thunderstorm activity associated with an approaching frontal boundary and its induced surface trough moves into the CWA. These conditions may lead to localized flooding & lightning hazard. * Northerly winds are expected to develop Monday into early Tuesday following frontal passage. * A low to moderate risk of rip currents exists across the coastal waters of Puerto Rico and the U.S. Virgin Islands. && .Short Term(Today through Monday)... Issued at 304 AM AST Sat Mar 21 2026 A quite warm and stable night was observed across the islands. A light southerly wind flow persisted during the night and early morning hours. Some clouds with showers were observed by Doppler radar and satellite imagery over the Caribbean coastal waters. As of 2 AM AST, the Doppler Radar showed light to moderate showers affecting the municipalities of Ponce and vicinity, leaving minimal rainfall accumulations. In terms of temperatures, the values remained just slightly above the climatological normals, with minimum temperatures in the upper 70s along the coast and in the upper 60s across the mountains, according to unofficial stations. For the rest of the day, variable weather conditions will prevail across the region under a southerly wind flow ahead of an approaching surface frontal boundary and its associated pre- frontal trough. In response to this evolving pattern, warmer-than- normal conditions are expected, with daytime temperatures rising approximately 2 to 3 degrees above climatological averages. Initially, relatively stable conditions will dominate during the morning hours; however, cloud cover will gradually increase as the frontal boundary continues to sink southward toward the islands. At the same time, moisture levels will rise, with precipitable water values increasing to around 1.3 to 1.5 inches by late morning and persisting through the remainder of the day. In combination with the pre-frontal trough and cooler temperatures aloft at 500 mb near -7C, development of showers its forecast across the southeastern quadrant of Puerto Rico, as indicated by high-resolution model guidance. Looking ahead, a wetter pattern is expected to become established by early Sunday as deeper moisture associated with the frontal boundary spreads across the forecast area from west to east, with showers and isolated thunderstorms reaching western Puerto Rico around 2 AM before gradually expanding across the remainder of the islands throughout the day. Consequently, mostly cloudy skies with periods of light to moderate rainfall are anticipated. Furthermore, the presence of the induced surface trough will weaken the pressure gradient, resulting in winds shifting to a west-southwesterly direction and decreasing in speed, which will favor slower-moving shower activity and increase the potential for higher rainfall accumulations. As a result, there is a moderate risk of urban flooding and rapid rises in small streams across the islands. By Monday, following the passage of the frontal boundary, winds are expected to veer to the north-northeast, promoting the advection of drier air and a more stable atmospheric profile, which will gradually reduce moisture levels and limit rainfall activity; although isolated showers may still develop over local waters and occasionally affect the northeastern coast, no significant flooding concerns are anticipated across the islands. For the U.S. Virgin Islands, Saturday will bring partly cloudy skies with only a few isolated showers. By Sunday, mostly cloudy conditions will prevail with more frequent passing showers as the frontal boundary settles over the region. The wet pattern will intensify into Monday, with shower activity becoming more persistent and organized as disturbances move in and out of the area. && .Long Term(Tuesday through Saturday)... Issued at 304 AM AST Sat Mar 21 2026 A broad mid- to upper-level trough will persist across the western Atlantic and northeastern Caribbean through the period, maintaining unsettled conditions across Puerto Rico and the U.S. Virgin Islands. Moisture will remain near to above normal throughout the period. On Wednesday, lighter steering flow and sufficient moisture will favor slow-moving showers, particularly across windward areas during the morning and over the interior and western portions of Puerto Rico during the afternoon. Thunderstorms are possible, with locally heavy rainfall that may lead to urban and small stream flooding as well as frequent lightning. From Thursday onward, moisture will deepen across the region while 500 mb temperatures remain below -8 degrees Celsius, resulting in a more unstable atmosphere. This combination of cold air aloft and abundant moisture through a deep layer will promote more efficient rainfall processes and an increased coverage of showers and thunderstorms each day. Periods of heavy rain will maintain an elevated risk of flooding, especially in areas that receive repeated rounds of precipitation. Gusty winds will be possible in and near heavier showers, while saturated soils will increase the likelihood of flooding, ponding of water on roadways, and minor landslides in steep terrain. Overall, an extended period of unsettled weather is expected from midweek through Saturday, driven by persistent troughing aloft, cold mid-level temperatures, abundant moisture at all levels, and periodic disturbances moving through the region. && .AVIATION... (06Z TAFS) Issued at 304 AM AST Sat Mar 21 2026 VFR conditions will persist, with brief MVFR conditions. Winds will remain VRB at 5 kts, gradually increasing to 8 to 10 kts from the S by 21/14Z. An approaching surface frontal boundary will result in lowering CIGS from 21/18Z onward as it sinks S into the CWA. Scattered -RA and SHRA, with possible VCTS, are expected to reduce VIS at TJPS between 21/19Z and 21/21Z. By 22/03Z, SHRA and VCTS with lower ceilings and reduced visibility are anticipated at TJBQ, with conditions potentially deteriorating to IFR. && .MARINE... Issued at 304 AM AST Sat Mar 21 2026 Light to moderate southeast winds will continue across the regional waters through at least today, maintaining light to moderate chop seas. A pre-frontal trough and associated boundary approaching from the northwest will weaken the pressure gradient, allowing winds to diminish and shift through the rest of the weekend. Periods of unsettled weather will also increase shower activity and the potential for thunderstorm development across the local waters, especially from this afternoon into the overnight hours. By early next week, high pressure building over the western Atlantic will promote a return to northeasterly winds and increasing seas, leading to deteriorating marine conditions. && .BEACH FORECAST... Issued at 304 AM AST Sat Mar 21 2026 Beach conditions have gradually improved as winds and seas have diminished across the coastal waters. However, a MODERATE risk of rip currents will persist through the weekend and much of the forecast period, mainly affecting the northern and eastern beaches of Puerto Rico, including Culebra, as well as the U.S. Virgin Islands. A moderate risk means that life-threatening rip currents remain possible, particularly for inexperienced swimmers. Beachgoers should remain cautious, stay near lifeguards, and avoid entering the water if unsure of conditions. A high risk of rip currents may be observed across northwest PR on Sunday. Lower risk conditions are expected along the more protected southern beaches, though caution is still advised. In addition, increasing moisture and instability associated with an approaching frontal boundary will promote periods of showers, and isolated thunderstorms cannot be ruled out, mainly from this afternoon into Sunday. Localized impacts, such as reduced visibility and brief gusty winds, may occur near showers, creating sudden hazardous conditions for beachgoers. There is a limited thunderstorm risk, but any storms that develop could produce lightning, posing a danger to those in or near the water. If thunderstorms approach, seek shelter immediately. For additional information and location-specific rip current details, please visit: weather.gov/beach/sju && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$