Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
078 FXCA62 TJSJ 172003 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 403 PM AST Fri Oct 17 2025 ...New SHORT TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... * For Puerto Rico, there is a limited to elevated flood threat, due to afternoon thunderstorms throughout the weekend. * For the U.S. Virgin Islands, a limited flooding risk and lightning activity this evening. * Hazardous marine and coastal conditions due to dangerous breaking waves and life-threatening rip currents from late Saturday night onward for the north-facing beaches of PR and the USVI. && .SHORT TERM...Tonight through Sunday... Issued at 400 PM AST Fri Oct 17 2025 A cluster of thunderstorms remained mainly across the coastal waters of St. Croix early in the morning, then remained between 20 to 40 miles south of st. Croix across the Caribbean Waters and Anegada Passage. Maximum heat index values were mainly between 100 and 106 degrees fahrenheit across coastal and urban ares of PR and the USVI. Winds were at 5 to 10 mph from the southwest due to the proximity of the frontal boundary. Thunderstorms moved across southwest PR by early afternoon, and the sea breeze then enhanced the formation of intense thunderstorms across the northern Atlantic waters of Puerto Rico. A nearly stationary frontal boundary interacting with deep tropical moisture will maintain unsettled weather across the northeastern Caribbean. We cannot ruled out showers and thunderstorms continuing tonight, mainly over the regional waters, but they may form overland too. Expect frequent lightning, gusty winds, and heavy rainfall near thunderstorms activity. On Saturday, the weakening front and upper trough will keep the pattern moist and unstable. Southerly winds will favor afternoon showers and isolated thunderstorms mainly over PR`s northern half with possible localized flooding. Activity may also extend to Vieques, Culebra, and portions of the U.S. Virgin Islands. Strong thunderstorms may cause frequent lightning, gusty winds, and heavy rainfall during the afternoon into the evening. By Sunday, as ridging builds from the east and winds turn southeasterly, a gradual drying trend is expected-first across the U.S. Virgin Islands and eastern Puerto Rico. However, lingering moisture and daytime heating will still trigger scattered afternoon convection across northwestern Puerto Rico, where minor flooding may occur. && .LONG TERM...Monday through Thursday... .From prev discussion issued at 515 AM AST Fri Oct 17 2025 A gradual improvement in weather conditions is expected beginning late Monday as a drier air mass filters across Puerto Rico and the U.S. Virgin Islands. Model guidance indicates precipitable water (PWAT) values decreasing to around or slightly below normal levels for this time of the year, while mid-level relative humidity also trends near normal. This drier and more stable air mass will promote a noticeable reduction in the frequency of showers and thunderstorm activity across the region. However, residual low-level moisture, combined with local effects and daytime heating, will still result in isolated to scattered afternoon showers, mainly across the interior and western Puerto Rico each day. Overall, the flooding threat should remain limited to none through midweek. This weather pattern should continue through midweek. By Thursday, model guidance suggests a gradual increase in PW, relative humidity, and wind speed as a tropical wave or possible tropical system moves near the local area. This will likely lead to a return of wetter conditions by the latter part of the workweek into the weekend. At this time, the National Hurricane Center forecasts a 10 percent chance of development in the next 48 hours and a 30 percent chance within the next 7 days. Regardless, residents and visitors are encouraged to continue monitoring the latest forecasts for any significant changes in conditions. && .AVIATION... (18Z TAFS) Issued at 400 PM AST Fri Oct 17 2025 VFR conditions will prevail today for all TAFs. However, a few TSRA will develop across the regional waters, and some of them may impact mainly the vicinity of local terminals. JPS has the best chance to observe a few TSRA moving inland through 17/22Z. TSRA could also develop near IST/ISX after 17/22Z. winds will prevail mainly from the S-SSW at 5-10 kts, becoming calm to light and VRB after 17/23Z. && .MARINE... Issued at 400 PM AST Fri Oct 17 2025 The nearby stationary boundary will continue to promote shower and thunderstorm activity across the regional waters and passages through Saturday. A long period northerly swell, associated to low pressure system over the northwestern Atlantic waters, is expected to reach the Atlantic waters and local passages around late Saturday night or early Sunday morning into the upcoming workweek. As a result, hazardous marine conditions are anticipated. Please, continue to monitor the forecast updates over the coming days. && .BEACH FORECAST... Issued at 400 PM AST Fri Oct 17 2025 A moderate risk of rip currents will persist across the north and east facing beaches through Saturday evening. Then, a long period northerly swell will gradually increase form late Saturday morning into early Sunday morning, reaching its making values around Sunday afternoon. This swell will create dangerous breaking waves and life-threatening rip currents along the west, north, and eastern beaches of the islands from Sunday into early next week. High surf conditions and minor coastal flooding are likely by Sunday, and will possibly extend into the early part of next week. Overall, dangerous swimming conditions, minor beach erosion, and life-threatening rip currents are expected from this weekend into early next week. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...CAM LONG TERM....MMC