


Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
332 FXCA62 TJSJ 181855 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 255 PM AST Sat Oct 18 2025 ...New SHORT TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... * Periods of heavy rainfall may cause urban and small-stream flooding, mainly across the interior and north-central areas of Puerto Rico. Expect dangerous lightning, gusty winds, and brief road and travel disruptions during afternoon storms. * Occasional Showers and thunderstorms will cross the US Virgin Islands, producing downpours, frequent lightning, and localized flooding. * Hazardous marine and coastal conditions are expected from late tonight into early next week along the northerly-facing beaches in PR and the US Virgin Islands. * Weather conditions will gradually improve by Monday, but the afternoon thunderstorms and showers will affect portions of the islands. && .SHORT TERM... (This evening through Sunday) Issued at 248 PM AST Sat Oct 18 2025 Thunderstorms persisted over St Thomas and St John early this morning, with rainfall amounts recorded by local weather stations ranging from 1 to 2.25 inches. A Flash Flood Warning and Flood Advisories were issued, respectively. Additionally, thunderstorms developed across the regional waters, creating hazardous conditions for mariners. Then, early this afternoon, thunderstorms developed across portions of PR, producing downpours, frequent lightning, and gusty winds. Heat index values across the islands were mainly between 100 and 106 degrees Fahrenheit, with isolated higher amounts. A nearly stationary frontal boundary interacting with deep tropical moisture will maintain unsettled weather across the northeastern Caribbean. PWAT values are above normal climatology, with RH values confirming saturation at mid-levels. Additionally, lapse rates are indicative of a strong instability, which will persist toward early Monday. Thus, afternoon convection will form today, creating frequent lightning, gusty winds, and heavy rainfall near thunderstorm activity. We cannot rule out showers and thunderstorms developing over the surrounding waters of the US Virgin Islands, moving inland later this afternoon or during the overnight hours. As a result, enhanced convergence between the weak frontal boundary north of the area and the return of the east-southeasterly flow could produce another round of showers or training storms over the windward portions of PR and the US Virgin Islands. As 925 mb winds strengthen from the southeast, increased moisture will foster showers and thunderstorms across the northern slopes and coastal plains by Sunday afternoon. Afternoon heating and sea- breeze convergence may lead to intense, slow-moving storms over the interior and north-central Puerto Rico, potentially causing urban and small-stream flooding. Although instability is high early in the day, mid-level warming will likely weaken convective strength later. On Monday, as the atmosphere aloft stabilizes under a moist atmosphere, we expect another round of afternoon convection mainly across western and interior PR. Although the overall coverage of rainfall is expected to be lower, there remains a possibility of isolated heavy downpours, lightning, and brief gusty winds. && .LONG TERM...Tuesday through Friday... Issued at 248 PM AST Sat Oct 18 2025 Tuesday is expected to be the driest and most stable day of the long-term period, as model guidance indicates precipitable water (PWAT) values decreasing to around or slightly below normal for this time of year. This drier and more stable air mass will help suppress widespread convective activity, leading to mostly fair weather conditions. However, localized afternoon showers cannot be ruled out, mainly across the interior and western sections of Puerto Rico due to daytime heating and local effects. Flooding potential remains minimal through this period. Wednesday will still be a generally fair day, with conditions remaining relatively stable during the morning hours. However, as the day progresses, a gradual increase in moisture content and mid-level humidity is expected, resulting in a higher potential for afternoon showers across portions of the interior and western Puerto Rico. This trend marks the beginning of a slow transition toward a wetter pattern. From Thursday onward, the forecast becomes increasingly dependent on the evolution of a system currently being monitored by the National Hurricane Center (NHC). At this time, the long-term forecast leans toward the GFS solution, which depicts a wetter pattern developing from Thursday into the weekend. The NHC currently assigns this disturbance a 0 percent chance of development within the next 48 hours and a 30 percent chance within the next 7 days. It is important to note that forecast confidence decreases significantly after Thursday, as there remains high uncertainty and notable discrepancies among model solutions regarding the development and possible impact for Puerto Rico and the U.S. Virgin Islands. Regardless of development, an increase in moisture and instability could lead to wetter and potentially unsettled conditions late in the week. Residents and visitors are advised to monitor the latest forecasts and updates from the National Weather Service and the National Hurricane Center for any significant changes. && .AVIATION... (18Z TAFS) Issued at 248 PM AST Sat Oct 18 2025 (18Z TAFs) Mostly VFR conds are exptd across all terminals. -TSRA/+TSRA across the CWA through 18/22z will promote VCTS mainly over JBQ, JPS, ISX, IST, and JSJ. TSRA nearby JSJ could reduce CIGs/VIS and promote MVFR conds until 18/22z. Winds will become light and VRB after 18/22z, increasing from the SE btwn 9 - 12 kt by 19/12 - 19/14z. && .MARINE... Issued at 248 PM AST Sat Oct 18 2025 A lingering frontal boundary and plenty of moisture will promote shower and thunderstorm activity across the regional waters and passages through at least late tonight. A long period northerly swell, propagating across the Atlantic Ocean, will slowly deteriorate the marine and coastal conditions later tonight through early next week. Thus, hazardous marine conditions are anticipated from around Sunday morning onward. Please, continue to monitor the forecast updates over the coming days. && .BEACH FORECAST... Issued at 248 PM AST Sat Oct 18 2025 A moderate to high risk of rip currents will persist across the north and east-facing beaches through this evening. Then, a long period northerly swell will gradually increase from late Saturday morning into early Sunday morning, reaching its maximum values around Sunday afternoon and overnight. 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 afternoon, and may 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...High Rip Current Risk through late Sunday night for PRZ001-002- 005-008-010-012. VI...None. AM...None. && $$ MORNING CREW...CAM/MNG EVENING CREW...ICP/YZR