Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
016 FXCA62 TJSJ 040936 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 536 AM AST Sat May 4 2024 .SYNOPSIS... A Flash Flood Watch remains in effect for all Puerto Rico and the U.S. Virgin Islands. Unstable conditions are expected to continue this afternoon influenced by an upper-level trough, an induced surface trough, and above-normal tropical moisture. In addition, lighter winds will continue to promote periods of heavy showers and strong thunderstorms across the local islands. The precipitable water content is forecast to remain above normal levels through most of the forecast period, with a drying trend anticipated late next week. && .SHORT TERM...Today through Monday... Thunderstorms and rain showers affected the US Virgin Islands overnight, where a Flood Advisory (St Thomas/St John) and a Flash Flood Warning (St Croix) were in effect overnight, saturating the soils. Additionally, yesterday`s rain activity saturated Puerto Rico soils even more, and most of the rivers` streamflows continued much above normal. Minimum temperatures were between 70 and 75 F along the coast and between 60 and 65 near mountains and valleys. Winds were calm to light and variable, promoting the development of land breeze. The weather pattern remains unstable and moist today, influenced by an upper-level trough with a jet stream, an induced surface trough, and above-normal tropical moisture pooling over the Northeast Caribbean. While we expect a brief respite in rain activity during the morning hours, the afternoon could see the formation of intense thunderstorms, particularly over and north of the Cordillera Central. Additionally, due to the dangerous river and soil status, these environmental and atmospheric conditions underscore the need to keep the Flood Watch in effect. Thus, we encourage everyone to stay updated and vigilant about the weather conditions. Be prepared for any changes. A surface high pressure will move into the Western Atlantic promoting that above normal moisture pools over Puerto Rico and the U.S. Virgin Islands Sunday and Monday. Regardless that we can anticipate periods without rain, the pattern will continue favorable for the formation of rain and afternoon thunderstorms. Given the significant amount of rain that we has received during the past week, any particular moderate to locally heavy rain will aggravate the potential to observe flooding and landslides (along steep terrains) across the islands. && .LONG TERM...Tuesday through Saturday... By the beginning of the long-term period, the latest models are suggesting a surface high pressure dominating over the western to central Atlantic. In our area, this will promote light to moderate winds from the east to northeast through the end of the workweek. At upper levels, another trough will pass mainly to our northfrom Tuesday through Thursday, maintaining unstable conditionsacross the islands. A moist airmass should linger over the local as moisture from the tropics will be pulled and join the remnants of the previous surface trough. The Precipitable Water (PWAT) model guidance shows values above normal climatological levelsthrough at least next Thursday; values around 2.00-2.25 inches. Consequently, the wet pattern is expected to continue with daily showers and possible isolated thunderstorms development. Shower activity should develop during the morning hours over portions of eastern PR and USVI, followed by afternoon convection over central and western PR resulting in greater accumulations. We encourage residents and visitors to remain weather-aware because any additional shower activity over saturated soils will further enhance the potential for flash flooding and mudslides. On the bright side, more stable conditions are forecast by the end of the week into the weekend as a mid-level ridge over the western Caribbean extends into the local area, bringing a drier air mass into the region resulting in more seasonal PWAT values and decreasing the potential for showers development. && .AVIATION... (06Z TAFS) Expect an unstable weather pattern, promoting the formation of SHRA/TSRA, especially in the afternoon and evening. VCTS/TSRA may continue to promote tempo MVFR to brief IFR conditions btwn 04/16- 23z near JSJ/JBQ/IST. Expect SSE/SE winds at 5 to 15 kt with sea breeze variations (aft 04/13z) and stronger gusts near heaviest SHRA/TSRA activity. && .MARINE... An induced surface trough moving across our area will yield lighter winds, while promoting shower and thunderstorm development through early next week. A surface high pressure extending from the western to central Atlantic will promote light to moderate trade winds across the regional waters through the forecast period. && .BEACH FORECAST... A fading northerly swell and light 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 through Sunday afternoon. Estimated rainfall totals around 3 to 5 inches in portions of Puerto Rico and 2 to 4 inches in Saint Croix, US Virgin Islands. Additional rainfall accumulations are expected to range from 2 to 4 inches. 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/AVIATION...CAM LONG TERM/MARINE....YZR