AFDSJU Area Forecast Discussion National Weather Service San Juan PR 311 AM AST Tue Mar 17 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH, FIRE WEATHER... .KEY MESSAGES... Issued at 258 AM AST Tue Mar 17 2026 * Hazardous marine and coastal conditions will persist through much of the week. Small Craft Advisories remain in effect for several local waters, and a high risk of rip currents is expected for many northern and eastern beaches of Puerto Rico and the U.S. Virgin Islands. * A front and associated trough will increase showers during the weekend. * Across the USVI, passing showers will increase late this afternoon through the evening hours. Breezy conditions expected early in the day. && .Short Term(Today through Thursday)... Issued at 258 AM AST Tue Mar 17 2026 A generally drier air mass continues to prevail across the region today. Total Precipitable Water satellite imagery confirms that Puerto Rico and the U.S. Virgin Islands are currently sitting in an area of relatively lower moisture. The latest forecast soundings show precipitable water (PWAT) values hovering near 1.0 inch today before gradually recovering. Because of limited moisture and breezy low-level winds, with 925 mb wind speeds starting the day around 25 knots, any showers that do develop will be fast moving and produce only minor rainfall accumulations. Hi- res model guidance supports this dry trend, showing localized accumulations mostly remaining under 0.20 inches through the day. Between late tonight and through early Wednesday morning, wind speeds will gradually decrease into the 15 to 20 knot range. At the same time, a weak trade wind perturbation will move through, bringing a brief surge in moisture that pushes PWAT values back toward climo normals at around 1.40 inches. Residents can expect a slight increase in shower activity associated with this moisture, primarily focused across the USVI and eastern sections of PR. Rainfall totals are forecast to remain relatively light, with isolated spots potentially seeing up to half an inch. An upper level ridge will continue to promote stable conditions aloft, and flood concerns will remain low. By Thursday, the weather pattern will become somewhat more active as deeper moisture pools over the islands. The GFS soundings show PWAT values rising further to 1.50-1.70 inches, accompanied by a sharp increase in mid-and low-level relative humidity. Furthermore, the trade winds will continue to subside, with 925 mb speeds dropping into the 10 to 15 knot range. This combination of lighter steering flow and increased atmospheric moisture will support a more typical shower pattern; ensemble rainfall models indicate enhanced precipitation coverage across the area, with localized accumulations potentially reaching near an inch. && .Long Term(Friday through Tuesday)... Issued at 258 AM AST Tue Mar 17 2026 Variable conditions are expected in the long-term forecast. A broad surface high pressure over the Central Atlantic will promote winds with a southerly component, with patches of moisture across the CWA on Friday. This will bring passing showers over windward sections in the morning, with afternoon showers over north/northwestern Puerto Rico. Rainfall accumulations should remain limited, leading to ponding of water over roadways and poorly drained areas. Weather conditions will likely become wetter and more unstable in the upcoming weekend, as a deep-layered trough with an associated frontal boundary will likely approach the region by Saturday, inducing a pre-frontal trough that will likely increase shower and thunderstorm activity. Additionally, a col region will move across the region by Saturday, with 925 mb winds plummeting to well below normal (mostly variable and calm winds). According to the latest model guidance, Precipitable Water values are expected to range between 1.5 and 1.75 inches, which is above the climatological normal, with the best moisture content in the low and mid levels (above 70%), increasing chances of scattered to numerous showers. Additionally, weakening winds will result in stationary showers and thunderstorms, with the highest potential of flooding on Saturday and Sunday. Due to the approach of the trough, the mid-level temperatures should slightly cool (around -8 degrees Celsius), with a jet streak positioning over the region, allowing ventilation aloft (between 70 and 90 kt). Although the best of convection should remain north of the CWA, conditions will likely be favorable for deeper convection and increasing lightning potential. Therefore, the most likely scenario is an advective pattern on both Saturday and Sunday, with afternoon convection over the mountain ranges of Puerto Rico. Rainfall accumulations will likely result in urban and small streams flooding, with a low chance of flash flooding, over the aforementioned areas. By Monday, another surface high pressure exiting eastern CONUS will increase pressure gradient, promoting E- ENE winds. Weather conditions should gradually improve; however, remaining moisture content should be enough for the development of showers across the regional waters into windward sections throughout the day, along with afternoon convection. Residents and visitors are encouraged to continue to monitor the weather forecast due to discrepancies between global solutions. Although Friday will likely be the warmest day of the long-term, maximum temperatures should remain in the mid to high 80s, with localized low 90s, across low elevation areas of the islands, with no heat threat expected. && .AVIATION... (06Z TAFS) Issued at 258 AM AST Tue Mar 17 2026 Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, by 17/20z -SHRA embedded in the trade winds will reach the USVI terminals, and shortly after the eastern PR terminals. This may lead to brief MVFR cigs and mostly VCSH/-RA periods. Winds will prevail from the E to ESE at 15-20 kt with gusts in the low 30s. && .MARINE... Issued at 258 AM AST Tue Mar 17 2026 The pressure gradient across the region will gradually loosen today and continue to diminish through the rest of the week. However, moderate to fresh easterly winds will persist across the regional waters. As a result, mariners can expect choppy to rough seas across much of the local waters. Therefore, Small Craft Advisories will remain in effect for most of the regional waters today. An easterly perturbation will increase shower activity across the regional waters around today. A frontal boundary along the eastern seaboard, moving eastward, will approach the northeast Caribbean later in the week, further easing the pressure gradient from Thursday through the end of the workweek. && .BEACH FORECAST... Issued at 258 AM AST Tue Mar 17 2026 Beach conditions will remain dangerous for inexperienced beachgoers across most of the local islands. Although winds are expected to be lighter than yesterday, lingering easterly winds will continue to generate choppy to rough seas across the regional waters. This will maintain elevated wave action along exposed beaches. As a result, a high risk of rip currents will persist for many of the exposed beaches across the islands, leading to dangerous swimming conditions. Beachgoers should remain alert to changing coastal conditions and continue monitoring the latest forecasts and statements. For additional information, please visit: weather.gov/beach/sju. .FIRE WEATHER... Issued at 258 AM AST Tue Mar 17 2026 A Fire Danger Statement will be issued once again for the coastal plains of southern Puerto Rico. The KBDI in Cabo Rojo was at 687 and 552 in Guanica. Southeast winds should prevail between 14 and 22 mph with gusts close to 30 mph. Passing light showers are expected early this morning, but drier air is expected throughout the day, dropping relative humidities between 45-55% along the south coast of PR. Therefore, the fire danger is elevated today across southern PR. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Wednesday afternoon for PRZ001>003- 005-007-008-011>013. VI...High Rip Current Risk through Wednesday afternoon for VIZ001-002. AM...Small Craft Advisory until 6 PM AST Wednesday for AMZ711-712-716- 723-726-733-735-741. && $$