Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
336 FXCA62 TJSJ 032037 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 437 PM 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 the prescence of an upper- level trough approaching the area from the west and an induced surface trough, increasing moisture levels. In adittion,lighter winds will continue to promote periods of heavy showers and strong thunderstorms across the local islands. && .SHORT TERM...Tonight through Sunday... An upper-level trough and an induced surface trough will promote wet and unstable conditions throughout the weekend, particularly tonight and Saturday. Tropical moisture from the Caribbean moving into the area is 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. Afternoon convection due to diurnal heating and local effects with the enhancing effects of the upper/surface trough will most likely bring the heaviest rainfall and strongest thunderstorms. An upper- level maxima will move across the islands during this time, with winds around 75 knots on Saturday which will enhance ventilation aloft to increase the possibility of storms. 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 -7 degrees Celsius, meaning that there is an increase in the potential for 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... //From previous discussion issued at 439 AM AST Fri May 3 2024// 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... (18Z TAFS) VRB weather conditions will persist through the period. Developing VCTS/TSRA will continue to promote tempo MVFR to brief IFR conditions. ESE winds up to 15 knots through 04/00z, then increasing again after 04/12Z. Stronger gusts near heaviest SHRA/TSRA activity. && .MARINE... A surface high pressure extending from the western to central Atlantic will promote light to moderate trade winds across the regional waters. An induced surface trough to our north will yield lighter east to east-southeast winds promoting shower and thunderstorm development across the area through early next week. && .BEACH FORECAST... A fading northerly swell and ligh winds will promote 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...ICP/MRR/RC LONG TERM....DSR/LIS AVIATION...MRR PUBLIC DESK/UPPER AIR/MARINE...GRS