Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
225 FXCA62 TJSJ 160849 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 449 AM AST Sun Mar 16 2025 .SYNOPSIS... Light and variable winds will dominate the region through the first part of the week. Afternoon convection will develop each day and will result in periods of moderate to locally heavy rain. Maximum temperatures will reach the mid and upper 80s, especially in urban and coastal areas. Another mid-to-upper-level trough will amplify from Tuesday onward, with moisture ramping up from Wednesday onward due to an approaching frontal boundary and prefrontal trough. && .SHORT TERM...Today through Tuesday... The night remained calm with primarily fair weather across the local islands. Minimum temperatures were slightly colder tonight, with stations in lower elevations reporting low to mid 70s, and localized areas in the upper 70s. Higher terrains observed low to mid 60s, and a station in Jayuya reported upper 50 temperatures. Current satellite-derived products show a drier air mass filtering into the region. Model guidance agrees that a drier trend will dominate for the short-term forecast, along with shallow convection in the afternoons. The surface low pressure northeast of the CWA will migrate to the north as it interacts with the high surface pressure in the western Atlantic. This will maintain variable NE winds today and on Monday, with a col region near the region that will additionally maintain light winds. Even though the PWAT values are expected to drop below the climatological normal (0.9-1.0 inch), the combination of local effects, diurnal heating, and sea breeze convergence will increase the chance of showers mainly over interior Puerto Rico. With the col region nearby, showers that develop in the area will likely stay longer and increase the chance of observing rainfall accumulations in roadways, urban, and poorly drained areas. On Tuesday, however, winds will continue to vary but with a westerly component as another frontal boundary and its pre-frontal trough approach the region. A deep layered trough will induce a low pressure near the region, increasing instability. However, the chance of convection activity will remain low due to below normal moisture content in the low and mid layers. Maximum temperatures today will once again remain in season, with urban and coastal areas in the mid to upper 80s and interior sections in the mid to upper 70s. There`s a trend of 925 mb temperatures increasing to above normal values, being Tuesday the warmest day of the period. .LONG TERM...Wednesday through Sunday... Moisture levels will begin to rise on Wednesday as the frontal boundary draws nearer to the islands from the west with a mid-to- upper-level trough increasing instability. From Thursday onward, moisture will pool from the east to east-southeast due to the prefrontal trough on Thursday and Friday. Thus, the second part of the workweek looks at this time unstable and with good available moisture to bring periods of flooding rains, especially in the afternoon and evening hours. By next weekend, the interaction between a high pressure migrating eastward from the Western to Central Atlantic with a surface low will promote moisture pooling over the Northeast Caribbean on Saturday and Sunday. && .AVIATION... (06z TAFs) VFR conds for all TAF sites. Shallow convection in the afternoon will bring -RA to JPS around 16/19z, which may temporarily reduce CIG/VIS. VRB winds with an NE component from 5-10 kt in the morning around 13-15z, then around 5 kt for most terminals after 16/23z. && .MARINE... A surface low and associated front northeast of the area will maintain light to moderate northeast winds for the next few days. A north-northeast swell will move across across the Atlantic waters and passages through early this week. Another cold front with its associated surface low will move eastward from the western to central Atlantic, approaching the region by the middle of the week and promoting the light and variable wind flow. && .BEACH FORECAST... A pulse of a long-period north-northeasterly swell spreading across the Atlantic waters and local passages will promote life- threatening rip currents along the north facing beaches from Rincon to Fajardo, Culebra and the northern US Virgin Islands. Therefore, the High Rip Current Risk continues in effect through late tonight. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through late tonight for PRZ001-002-005- 008-010-012. VI...High Rip Current Risk through late tonight for VIZ001. AM...None. && $$ SHORT TERM/AVIATION...MNG SYNOPSIS/LONG TERM/MARINE/BEACH FORECAST....CAM