Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
285 FXCA62 TJSJ 292148 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 548 PM AST Mon Apr 29 2024 .SYNOPSIS... The surface high pressure over the western Atlantic will continue to promote breezy northeasterly winds through at least midweek. Moisture content will oscillate between normal to above-normal values tonight resulting in additional showers tonight and Tuesday. By mid-week onwards, instability and moisture levels increase once again as a mid to upper level trough lingers over the western Atlantic and lighter east to southeast winds return. Coastal and marine conditions will remain hazardous through at least late Wednesday. && .SHORT TERM...Tonight through Wednesday... During the morning hours until noon, the isolated to scattered showers moved through the northern, eastern, and interior sectors of PR and the US Virgin Islands. Doppler radar estimates showed about an inch of rain in Rio Grande and surrounding municipalities. By early afternoon, rain continued to move into those areas. Additionally, the development of more intense showers was recorded over the southwest of PR. At the moment, the Doppler radar estimated between 2 and 4 inches of rain over the municipalities of the SW of PR, where a Flood advisory continues in effect. Maximum temperatures were from the mid-to-upper 80s across coastal areas to the 70s and lower 80s across higher elevations. Tonight into Tuesday morning, additional showers are anticipated to develop across portions of the USVI, northern and eastern sectors of Puerto Rico, and the Caribbean waters along with some breezy and gusty periods. By Tuesday afternoon, expect another active day with diurnally induced afternoon convection over portions of the interior and south/southwest PR. We encourage residents and visitors to remain alert and exercise caution on the roads as soils are saturated and rain activity may result in additional floodings. For the rest of the period, the main weather feature continues to be a broad surface high pressure moving slowly toward the Central Atlantic during the next few days. The surface high will promote breezy conditions with moderate to fresh northeasterly winds through at least tomorrow, then winds will shift from the east to southeast and become light to moderate on Wednesday as the surface high weakens. By the end of the period, an upper-level trough approaches the area from the west and an induced surface trough develops over the northeastern Caribbean. Precipitable Water (PW) models suggest values above the normal climatological levels for this time of the year. This will enhance shower and thunderstorm development across much of Puerto Rico. For that reason, the risk of flooding will likely remain elevated across most islands, especially during the afternoon hours. It is crucial to be cautious and aware of these potential risks. High temperatures will remain in the mid-to-upper 80s along the coastal and urban areas and in the mid-to-upper 70s along the mountains and valleys. Minimum temperatures will range from the upper 70s to low 80s across coastal areas to the mid-60s in the higher elevations. && .LONG TERM...Thursday through Monday... .PREV DISCUSSION... /issued 434 AM AST Mon Apr 29 2024/ The inherited forecast remains unchanged. Recent model guidance suggests a mid-to-upper-level trough developing and staying nearly stationary over the west to southwestern Atlantic, at least through the long-term period. From Thursday onwards, expect the winds to become lighter as the surface high pressure north of the area continues to weaken. By Thursday, remnants of an old frontal boundary will reach the island from the northeast and merge with a trough or perturbation over the northeastern Caribbean. This will lead to unstable and wetter weather conditions across Puerto Rico and the U.S. Virgin Islands, with possible flooding impacts and mudslides in areas of steep terrain across Puerto Rico. At this time, Precipitable Water (PW) models suggest values above two standard deviations and, therefore, above the normal climatological levels for this time of the year. We anticipate active afternoons during the long-term period, with possible flooding impacts and mudslides in areas of steep terrain across Puerto Rico. For the USVI, an increase in the frequency of showers and isolated thunderstorms is possible from Thursday onwards. Heat indices across the lower elevations of the islands could likely range between 102 and 106 degrees on Friday and Saturday before the onset of afternoon convection. Overall, an unstable and wetter patternis expectedto evolve over thelong-term. && .AVIATION... (18z) TAFS VCSH and period of SHRA are possible tonight into tomorrow morning across TJSJ and USVI TAF sites. Tomorrow around 14Z, possible TSRA in TJPS and prevailing VCSH across the rest of the sites. NE winds at 12 or less during the overnight period, increasing tomorrow morning with stronger gusts near 25-30 kt during the day. && .MARINE... A sub tropical high pressure across the western Atlantic will continue to promote moderate to fresh trade winds through at least Wednesday night. As a result, expect hazardous seas for small craft operators due to confused seas associated with the increasing winds and a northeasterly swell spreading across the local waters. Small Craft Advisories are in effect for the Atlantic waters and most local passages. && .BEACH FORECAST... A northerly swell and stronger winds are resulting in High Risk of Rip Currents across beaches from Mayaguez to Fajardo, Culebra, and USVI through at least late Wednesday. For more information and details about the latest forecast please refer to the Surf Zone Forecast (SRFSJU) and the Coastal Hazard Message product (CFWSJU). && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through late Wednesday night for PRZ001- 002-005-008. High Rip Current Risk through late Wednesday night for PRZ010- 012. VI...High Rip Current Risk from Tuesday morning through late Wednesday night for VIZ001. High Rip Current Risk from Tuesday morning through Tuesday afternoon for VIZ002. AM...Small Craft Advisory until midnight AST Wednesday night for AMZ711-712. Small Craft Advisory until 6 PM AST Wednesday for AMZ716. Small Craft Advisory until noon AST Wednesday for AMZ723-742. Small Craft Advisory until noon AST Wednesday for AMZ741. && $$ SHORT TERM/MARINE/BEACH FORECAST...YZR AVIATION..YZR/CVB LONG TERM....MMC PUBLIC...ERG