Hurricane Season runs from June 1-November 30
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Area Forecast Discussion (AFD)
851 FXCA62 TJSJ 261757 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 157 PM AST Sat Sep 26 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 138 PM AST Sat Sep 26 2026 - Afternoon showers and thunderstorms will produce an elevated risk of urban and small stream flooding today across interior, north-central, and western Puerto Rico. Weak tropical wave will enhance the potential for shower and thunderstorm activity tomorrow, Sunday. - A Heat Advisory remains in effect through at least 4 PM AST today across coastal and urban areas of Puerto Rico and the U.S. Virgin Islands. Elevated heat risks will persist through the weekend. - A moderate risk of rip currents continues along northwestern to eastern beaches of Puerto Rico and the northern U.S. Virgin Islands through tomorrow, Sunday. High risk of rip currents is possible on Monday due to a small northerly swell. && .Short Term(This evening through Monday)... Issued at 138 PM AST Sat Sep 26 2026 As expected, mostly sunny skies prevailed this morning across the local area, with a few isolated passing showers affecting portions of the U.S. Virgin Islands (USVI) and very isolated spots near eastern Puerto Rico. The mostly sunny skies have allowed temperatures to rise, which, combined with light east-southeasterly winds and available moisture, is driving heat indices above 100 degrees across many coastal municipalities, as well as urban areas and valleys across Puerto Rico and the USVI. The Heat Advisory remains in effect through at least 4 PM AST this afternoon. Therefore, people are urged to stay well-hydrated and take breaks to adequately cool down if outside. Compared to previous days, drier air is being observed today, with the 26/12z TJSJ sounding showing a precipitable water value of 1.56 inches, below normal for this time of the year. The sounding also showed a light southeasterly flow with winds of 5 to 6 knots between the surface and 3 km, a very weak to absent low-level temperature inversion, a 500-millibar temperature of -7.3 degrees Celsius (near the 25th percentile for this period), and a DCAPE of around 1100 J/kg. These conditions, combined with available moisture, strong daytime heating, and local effects, will promote showers and thunderstorms during the afternoon across the interior and north- central to northwestern quadrants of Puerto Rico. Despite the drier air, mid- to upper-level instability associated to the close proximity to an upper-level trough centered just east of the USVI, supports the potential for locally strong thunderstorms capable of producing frequent lightning and locally strong gusty winds across some those areas. Additionally, the light steering flow could produce prolonged periods of rainfall and, considering recent rains across these areas, will promote an elevated flood risk today with the potential for urban and small-stream flooding. Streamers will continue to be possible downwind from El Yunque and all the islands during the afternoon, with the El Yunque streamer favoring the potential for shower activity across the northern half of the San Juan metropolitan area. Otherwise, mainly tranquil weather conditions will continue. For tonight, passing showers may affect portions of eastern Puerto Rico and the USVI, but no significant impacts are expected. For Sunday, the steering flow will shift to a more east- southeasterly direction rather than southeasterly. Slightly higher moisture, but still within seasonal values, will enter the region due to a tropical wave passing mainly south of our area, while the upper-level trough remains just east of the local area. Hence, tomorrow is still expected to be the most active day in terms of convective activity, with the potential for more frequent passing showers in windward areas throughout the day and more numerous showers and thunderstorms in the afternoon favoring the western interior and western to northwestern quadrants of Puerto Rico, as well as afternoon streamers downwind from El Yunque and the USVI. Similar to today, some thunderstorm activity could be locally strong with frequent lightning and gusty winds. Heavy rainfall will pose an elevated flooding risk, including water accumulation on roads and poorly drained areas, urban and small-stream flooding, and quick rises along susceptible rivers. Saturated terrain will also remain vulnerable to landslides. By Monday, a more typical weather pattern will return, with passing morning showers over windward areas and afternoon convection favoring interior, western, and northwestern Puerto Rico. The rainfall hazard should become more localized due to drier air and a stronger east-southeasterly steering flow. An elevated heat threat will continue to be a concern during the warmest hours through at least Sunday, and it could possibly continue into Monday, especially where prolonged morning and early- afternoon sunshine occurs. For that reason, we urge people to monitor the forecast and practice heat safety. && .Long Term(Tuesday through next Friday)... Issued at 153 AM AST Sat Sep 26 2026 Drier conditions than those usually seen for the season are expected throughout the long term period. While model guidance indicates some variability, with the GFS showing more favorable conditions on Tuesday, the majority of the humidity will be centered in the low levels of the troposphere while drier conditions will dominate the low-to-upper levels (700-250hPa). An upper-level low pressure system will be located to the northeast of the US Virgin Islands and Puerto Rico at the beginning of the week and will shift to the southeast of the region by the end of the week eventually moving away from the CWA by the end of the forecast period. While these conditions will act to limit shower and thunderstorm activity, other factors may favor more active periods over the islands. Mid tropospheric temperatures remain favorable for the development of deep convective cells. Local effects will act as the main drivers of activity particularly over the US Virgin Islands and eastern Puerto Rico in the mornings and the interior and northwestern Puerto Rico in the afternoons. Increasing surface winds may also favor the development of streamers from the US Virgin Islands, Vieques, Culebra and El Yunque rainforest. Conditions are expected to become more enhanced by Friday afternoon when a more humid vertical profile returns increasing the potential for the development of convection. Citizens and visitors are invited to remain weather ready and stay updated of the evolving weather conditions. The long term period might also bring a respite from the elevated heat risks and the 925 mb temperatures show a decreasing trend, suggesting more amenable conditions might prevail as the week progresses. Nonetheless, individuals are recommended to stay alert as these forecasted conditions may change. && .AVIATION... (18Z TAFS) Issued at 138 PM AST Sat Sep 26 2026 Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, locally induced afternoon TSRA/SHRA may develop in and around TJBQ/TJSJ btw 26/19-22z. The 26/12z TJSJ sounding indicated ESE winds up to 10 kt blo FL050. && .MARINE... Issued at 138 PM AST Sat Sep 26 2026 Light to moderate east to southeast winds of 10 to 15 knots or less and seas generally between 2 and 4 feet will prevail today. Marine conditions will gradually deteriorate from Sunday into early next week as a northerly swell spreads across the Atlantic waters and passages while easterly winds strengthen. Seas will build to 5 to 6 feet across portions of the Atlantic waters and local passages, with occasional seas up to 8 feet possible by Monday night. Scattered showers and isolated thunderstorms may also result in locally higher winds and seas, frequent lightning, and brief reductions in visibility during the afternoons across the west/northwestern waters of Puerto Rico. && .BEACH FORECAST... Issued at 138 PM AST Sat Sep 26 2026 A moderate risk of rip currents will prevail through the weekend along the west through northeastern beaches of Puerto Rico, as well as Culebra and the U.S. Virgin Islands. A high risk of rip currents is possible by Monday as winds increase slightly across the Atlantic coastal waters, and a small northerly swell spreads across the Atlantic waters and passages. Additional beach hazards include heat and isolated thunderstorms, especially across western Puerto Rico, where lightning, brief heavy rainfall, and gusty winds may occur during the afternoon hours. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>013. VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002. AM...None. && $$ SHORT TERM...KML LONG TERM...RVM/MRR AVIATION/BEACH/MARINE...DSR
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