Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
303 FXCA62 TJSJ 161818 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 218 PM AST Wed Sep 16 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 159 PM AST Wed Sep 16 2026 - An approaching tropical wave will continue to promote showers and thunderstorms across the U.S. Virgin Islands and Puerto Rico through the rest of the afternoon into Thursday, increasing the potential for flooding and lightning risks. - There is a low to moderate risk of rip currents through the weekend along the beaches of the U.S. Virgin Islands and Puerto Rico. - Limited extreme heat risks are expected for the rest of today and Thursday, with elevated to significant hazard risks returning Friday into the weekend. - Weather conditions are expected to improve by Thursday evening into Friday, as a drier airmass and low concentrations of Saharan dust filter into the area. && .Short Term(This evening through Friday)... Issued at 159 PM AST Wed Sep 16 2026 A few passing showers have reached the U.S. Virgin Islands and eastern portions of Puerto Rico. The combination of an approaching moist, unstable tropical wave, a nearby upper-level low, and local effectssuch as diurnal heating, orographic lift, and sea-breeze convergencewill fuel deep convection today. The axis of the tropical wave is currently crossing the U.S. Virgin Islands; however, the main moisture field is preceding it. Consequently, shower activity and isolated thunderstorms will increase across the islands this afternoon as the wave moves through the Forecast Area (CWA). The most active weather is expected overnight, with activity ramping up across the U.S. Virgin Islands, eastern Puerto Rico, and the metropolitan areas before extending into the interior and western regions. Precipitable Water (PWAT) values will exceed seasonal values (1.952.30 inches) by this afternoon as wave- associated moisture moves in. Unstable atmospheric conditions will prevail, supported by steep mid-level lapse rates (700500 mb) reaching over 6.5 C/km. The bulk moisture associated to the wave will remain until Thursday evening. Drier air is forecasted to approach the islands by Friday, which could limit convection, however showers and thunderstorms activity is still possible. Mostly advective showers are expected during morning hours on Thursday, along isolated thunderstorms. The upper-level low is expected to depart the region tomorrow, however, it should still support instability combined with the tropical wave. Although limited daytime heating could limit deep convection in the afternoon, showers and thunderstorms are still expected. Based on this scenario, the risk of excessive rainfall remains elevated for the rest of today and tomorrow across eastern, northern, interior and western portions. A limited excessive rainfall risk is expected on the U.S. Virgin Islands and rest of the area. These risk levels from limited to moderate will persists until Friday. These risks means that flooding is possible in urban areas, roads, small streams and washes, and a low chance of urban and small streams is present. Also, over most areas, ponding of waters in roads and poorly drained areas is possible. The heat risk remains limited until Thursday due to cloud cover associated with the tropical wave. However, the risk will increase by Friday as a drier air mass along with Saharan dust filters into the area. && .Long Term(Saturday through next Tuesday)... Issued at 159 PM AST Wed Sep 16 2026 During the early part of the long-term period, an upper-level low northeast of the Caribbean will induce above-normal low-level moisture across the region, while a weak surface high pressure north- northwest of the area draws an east-southeasterly wind flow over the local area. Precipitable water (PWAT) values between 2.0 and 2.2 inches are expected, remaining slightly above normal for this time of year. Despite this moisture, a mid-to-upper level ridge will dominate the area, maintaining unfavorable upper-level conditions and sustaining a seasonal pattern. Passing showers are expected during the morning hours across the regional waters and windward sections of the islands, followed by afternoon showers and isolated thunderstorms over the interior and western sections of Puerto Rico, as well as downwind from El Yunque, Puerto Rico`s smaller islands and the US Virgin Islands. By Sunday, winds are expected to shift to southeasterly, focusing afternoon convection primarily over the interior and northwestern Puerto Rico. Weak steering winds around 10 knots will elevate the flood risk where persistent showers develop. By Sunday night into early next week, the moist southeasterly flow will pull more tropical moisture into the area, holding PWAT values around 2.0 inches (seasonal to slightly above normal). The mid-to- upper level ridge and the upper-level low to the northeast will both remain in place, continuing the seasonal regime under east- southeasterly winds. Morning showers will favor eastern and southeastern portions of the islands, including the US Virgin Islands, with afternoon convection concentrating across the interior and northwestern quadrant of Puerto Rico. With 500 mb temperatures hovering near -6C, isolated afternoon thunderstorms will remain possible each day. Additionally, the moist southeasterly flow will drive an elevated heat risk from Sunday onward, primarily impacting heat-sensitive individuals without access to effective cooling or hydration. By mid-week, a tropical wave may approach the area, though forecast uncertainty remains due to model disagreement, with the GFS bringing the wave closer to the local area, while the ECMWF pulls it to the north. Please continue to monitor the forecast for future updates as guidance resolves. && .AVIATION... (18Z TAFS) Issued at 159 PM AST Wed Sep 16 2026 A combination of VFR and MVFR conds are expcd across all TAF sites, as a tropcl wave moves across the CWA, bringing -TSRA/+TSRA throughout the TAF prd. TEMPOs btwn 16/18-20 over JSJ and ISX due to reduced CIGs/VIS, leading to MVFR/IFR conds. AMDs will be issued if required. Elsewhere, mainly VCTS with PROB30s btwn the 12/06-16 prd for the eastern TAF sites of PR and USVI due TSRA. E-SE winds btwn 12 - 18 kt with gusts up to 25 - 28 kt through 16/22 - 23z, slightly weakening and becoming 5 - 10 kt. Winds should strengthen once again btwn 10 - 15 kt, gusts up to 25 kt, by 17/12-13z. && .MARINE... Issued at 159 PM AST Wed Sep 16 2026 An approaching tropical wave and a broad surface high will maintain winds around 10 to 20 knots, resulting in periods of locally light to moderate chop. The most unsettled conditions are expected tonight into Thursday, with increased showers and thunderstorms. Small craft operators should exercise caution. Conditions will gradually improve Friday as the wave moves west, with moderate easterly trade winds persisting through the weekend. && .BEACH FORECAST... Issued at 159 PM AST Wed Sep 16 2026 Expect a low to moderate risk of rip currents across Puerto Rico and the U.S. Virgin Islands, as a tropical wave moves across region tonight into Thursday. This will bring winds of 17 to 23 mph, along with squally showers and thunderstorms. Beachgoers should seek shelter immediately if thunder is heard. Remember, life-threatening rip currents can still occur during low-risk conditions, particularly near groins, jetties, reefs, and piers. A more widespread moderate risk is forecast Friday along the north-facing beaches of Puerto Rico, followed by a generally low risk through the weekend. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ KEY MESSAGES...GRS SHORT TERM...GRS/MNG/JCP LONG TERM...CAM/KML MARINE/BEACH FORECAST...MMC AVIATION...MNG