705 FXCA62 TJSJ 272045 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 445 PM AST Sun Apr 27 2025 .SYNOPSIS... An unsettled weather pattern is expected to continue through at least Thursday due to a series of troughs and abundant moisture. The likelihood of urban and small stream flooding due to strong showers and thunderstorms, as well as mudslides and rapid river rises will remain high along with a chance of isolated flash flooding as well. While there is some uncertainty in the location and timing of this rain, there is a high confidence of a wet and unsettled period for Puerto Rico, the Virgin Islands and local waters. A high rip current risk is in effect for the northern exposed beaches of Puerto Rico, from Aguadilla to Fajardo and Culebra through at least late tonight. && .SHORT TERM...Tonight through Tuesday... Showers and thunderstorms impacted mainly the eastern third of PR and the US Virgin Islands throughout the morning, producing flash, river, and urban flooding. Since midnight, the highest radar- estimated rainfall accumulations ranged from around 1.0 to 2.0 inches, with isolated rainfall amounts of up to 4 inches. Then, thunderstorms moved across the interior and north central locations of PR, where estimated ranged between 2 and 3 inches. The maximum temperatures observed ranged in the mid or upper 80s across the western half portion of PR, where rain developed around noon. Today`s winds were mainly from the ESE-SE at 10 mph but gusty near thunderstorms and with sea breeze variations. For tonight, we anticipate that today`s afternoon convection slowly dissipates from the interior and western sections of Puerto Rico by this evening. However, the unstable pattern will continue due to the proximity of the deep layer trough and abundant moisture moving in from the east. Remember that soils are saturated, and rivers and stream flows are elevated. Thus, any persistent moderate or heavy rain can lead to flooding issues, including minor, flash, or river flooding, as well as landslides in steep terrain. We also expect another round of inclement weather, spreading from the surrounding waters into the local islands overnight and tomorrow early morning (Monday), affecting mainly across the US Virgin Islands and the eastern third of Puerto Rico. At the beginning of the workweek, we anticipate that the wet and unstable weather pattern will persist due to the influence of the mid-to-upper trough and abundant tropical moisture. Although model guidance indicates a slight decrease in moisture content, it will remain above normal to average, thus sustaining the wet conditions. The most significant precipitation activity is expected primarily during the afternoons and early evenings. Beginning Monday night, winds will shift from the east to the northeast, resulting in afternoon showers and thunderstorms concentrating more to the southeast of the main island. Residents and visitors are advised to stay informed about the weather and monitor official forecast updates, particularly because of the ongoing flood risk, which is the primary concern. The threat of unexpected landslides along steep terrains is also a concern. .LONG TERM...Wednesday through Sunday... ./FROM PREV DISCUSSION...Issued at 453 AM AST Sun Apr 27 2025/ A wet and unstable weather pattern will persist through the early part of the long-term forecast. A surface high-pressure system over the western Atlantic and a surface low over the central Atlantic will induce east-northeast winds across the CWA. These northeast winds will promote low-level convergence over the region, particularly on Wednesday and Thursday, when the surface low will be closest to the northeast. Precipitable water content is expected to remain between 1.7 and above 1.9 inches. These values exceed the 75th and 90th percentiles of the climatological normal, indicating a continuation of well-above-normal moisture levels for this time of year. In terms of instability, the surface low is being induced by an upper-level cut-off low. These features will lead to a further drop in 250 mb height fields, cooler 500 mb temperatures, and steeper lapse rates, sustaining unstable weather conditions capable of generating deep convective activity. The likelihood of convection will be highest during the afternoon hours, as high moisture content and instability combine with surface heating and local effects. Soils are expected to remain somewhat saturated by Wednesday due to rains from previous days, with rivers still experiencing elevated streamflows. Consequently, the flood risk will remain elevated through at least Thursday, particularly during the afternoon hours. Quick river rises, river flooding, and landslides are also possible, primarily across Puerto Rico. In the U.S. Virgin Islands, minor flooding with brief periods of excessive runoff is possible each day of the week. Some ridging aloft will bring somewhat more stable weather conditions by the end of the workweek into the weekend. Nevertheless, enough low-level moisture could combine with diurnal heating and local effects during the afternoon to promote convective activity in localized areas. && .AVIATION... (18Z TAFS) SHRA/TSRA will continue to impact the local flying area throughout the forecast period. Terminals could be affected by this activity, producing periods of MVFR or even IFR. Thus, TEMPOs will be mainly required for the following time frames: 18-23z across JBQ/JSJ and 03- 12z near IST/ISX/JSJ. Winds will prevail between 10 and 15 kt, mainly from the ESE/SE under sea breeze variations, becoming calm to light and variable after 27/23z, returning from the ESE at around 10 kt after 28/13z with sea breezes. && .MARINE... Light to moderate east to southeast winds will prevail through at least tonight, backing from the northeast winds early this week. A deep layer trough will continue to promote an unstable weather pattern across the local waters. Thus, showers and thunderstorms are expected to persist, producing localized hazardous marine conditions. This unstable and wet pattern will prevail through at least midweek. A long-period northeasterly swell is spreading across the Atlantic waters. Therefore, small craft should exercise caution. && .BEACH FORECAST... A northeasterly swell of 12-14s is being detected by the CariCOOS buoys near Rincon, San Juan and Vieques. There is a High Risk of Rip Currents through at least 6 AM AST tomorrow, Monday, for the north- facing beaches of Puerto Rico, from Aguadilla to Fajardo, and Culebra. A High Risk of Rip Currents means that life- threatening rip currents are likely in the surf zone. A moderate risk of rip currents is also forecast for tonight for the beaches of Aguada, Rincon, northern Vieques, northern St. Thomas, northern St. John and northeastern and eastern St. Croix. Low risk elsewhere, however, life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. For more information, please refer to the latest Coastal Hazard Message (CFWSJU) and Surf Zone Forecast (SRFSJU). Residents and visitors in affected regions should heed warnings, avoid swimming in these waters, and stay informed about updates from local authorities. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through late tonight for PRZ001-002-005- 008-012. VI...None. AM...None. && $$ SHORT TERM...CAM/ICP LONG TERM....MRR/GRS
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