Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
861 FXCA62 TJSJ 030839 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 439 AM AST Fri May 3 2024 .SYNOPSIS... A Flash Flood Watch is in effect for all Puerto Rico and the U.S. Virgin Islands. Unstable conditions (due to an upper-level trough approaching the area from the west and an induced surface trough), increasing moisture, and lighter winds will promote periods of showers and thunderstorms across the local islands, particularly today through Saturday. The precipitable water content is forecast to remain at normal to above normal levels through the long term period, with a drying trend late next week. && .SHORT TERM...Today through Sunday... During the overnight hours, the eastern half of Puerto Rico experienced some rainfall and thunderstorm activity. The highest accumulations were observed in municipalities like Humacao, Naguabo, and Yabucoa, with around 1 to 4 inches of rain. Fajardo, Luquillo, and Ceiba also experienced rainfall rates of around 1 to 3 inches, where Flood Advisories were issued. The island of St. Croix also experienced some rainfall, but accumulations were not significant. Overall, the eastern sections of Puerto Rico had an active night, while the western sections experienced calm weather conditions. Minimum temperatures were in the 70s to low 80s across coastal areas and the upper 60s to low 70s across the mountainous areas. The short-term forecast remains on track. An upper-level trough and an induced surface trough will promote wet and unstable conditions throughout the weekend, particularly today and Saturday. Tropical moisture from the Caribbean will also move into the area, increasing the chances for widespread rainfall and flooding through this weekend. Showers and thunderstorms continue to be the dominating weather features through at least Sunday, particularly along the eastern half of Puerto Rico and the U.S. Virgin Islands. By the end of the workweek into the weekend, an upper-level maxima will move across the islands with winds around 70 knots. The Precipitable Water (PWAT) model guidance shows values in the 75th percentile or above normal climatological levels through the weekend. The 500 mb temperatures also suggest values around -8 degrees Celsius, meaning that there is an increase in the potential for some isolated thunderstorm activity across Puerto Rico and the U.S. Virgin Islands. As saturated soils prevail, any brief period of heavy showers or persistentlight rainfall could lead to urban andsmall- streamflooding, localized flashflooding, and mudslides, particularly across the interior, the eastern half of Puerto Rico, and the U.S. Virgin Islands. A Flood Watch was issued through Sunday afternoon. We encourage citizens and visitors to be aware of any additional updates in the forecast. .LONG TERM...Monday through Friday... Wet and unstable conditions should continue through midweek next week. If the rainfall forecast materializes during the short- term period, any additional shower activity over saturated soils will further enhance the potential for flash flooding and mudslides. Residents and visitors are encouraged to monitor the evolution of the weather conditions over the long-term period. A surface high pressure is expected to build over the western Atlantic during the first part of the week. This will promote moderate winds from the east to northeast through the end of the workweek. In addition, the remnants of the previous surface trough to our north or just across the northeastern Caribbean are expected to merge with a frontal boundary across the central Atlantic and linger over the local area through at least Thursday. At upper levels, another trough will pass mainly to our north from Tuesday through Thursday, maintaining unstable conditions across the islands. The highest precipitable water (PWAT) values are expected during this period, with global guidance suggesting 2.00-2.25 inches of PWAT. Daily rainfall amounts could range between 1 and 3 inches, with the highest accumulations in diurnal activity over portions of eastern, central, and western PR. More stable conditions are forecast for Friday as a mid-to-upper level ridge over the western Caribbean extends into the local area, bringing drier air aloft and causing the PWAT to drop to around 1.50 inches. && .AVIATION... (06z) TAFS VRB weather conditions are fcst to persist throughout the period. Expect VCTS to develop after 03/14Z at TJSJ/TIST/TISX and after 03/18Z at TJBQ/TJPS causing tempo MVFR to brief IFR conds. ESE winds at 04-16 kt with higher gusts near heaviest showers. && .MARINE... A surface high pressure extending from the western to central Atlantic will promote light to moderate trade winds across the regional waters. Seas should remain between 2 and 5 feet during the next few days, with the highest seas expected across the offshore waters. An induced surface trough to our north will yield lighter east to east- southeast winds and promote shower and thunderstorm development across the area through early next week. && .BEACH FORECAST... Fading swell and lighter winds will promote mainly a low to moderate risk of rip currents during the next several days. However, flooding rains and thunderstorms are expected through the weekend across the islands. && .HYDROLOGY... A Flash Flood Watch remains in effect for all of PR and the USVI from this morning through Sunday afternoon. Rainfall totals between 3 and 6 inches and locally higher are possible through the weekend. Please refer to the latest Flash Flood Watch (FFASJU) for more information. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Flood Watch through Sunday afternoon for PRZ001>013. VI...Flood Watch through Sunday afternoon for VIZ001-002. AM...None. && $$ SHORT TERM...MMC LONG TERM....DS AVIATION...MMC