Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
678 FXCA62 TJSJ 280855 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 455 AM AST Sun Apr 28 2024 .SYNOPSIS...A surface high pressure over the western Atlantic will promote northeasterly winds through at least Wednesday. Breezy conditions are possible during the start of the workweek. Drier air between a surface low over the north central Atlantic and the surface high should reach the local area under the northeasterly fetch. However, moisture content should remain at normal levels. By mid-week onwards, instability and moisture levels increase once again as an upper level trough lingers over the western Atlantic and lighter east to southeast winds return. Life-threatening rip currents are expected during the first part of the week. && .SHORT TERM...Today through Tuesday... Calm weather conditions prevailed across Puerto Rico and the U.S. Virgin Islands, with quick passing showers over the local waters. Low temperatures were observed in the range from the mid to upper 60s across the higher mountains and valleys, and from the low to mid 70s along the coastal areas. Breezy conditions prevailed across the islands under a northeasterly wind flow. Today, we expect mostly tranquil weather conditions during the morning hours, with passing showers moving into the eastern coast of Puerto Rico and the U.S. Virgin Islands at times. During the afternoon hours, rainfall development is likely over portions of the interior and southwest Puerto Rico due to lingering moisture of a trough/frontal boundary in combination with daytime heating and local effects. Precipitable water content values are in the range between 1.45 to 1.60 inches. Showers and isolated thunderstorms across the mentioned sectors may result in flooding, river rises, mudslides and isolated flash flooding. Soils are very saturated due to the rains from the previous weeks, and any additional accumulations could result hazardous. We continue to encourage citizens of Puerto Rico and visitors to closely watch the weather conditions during the next several days due to the potential for showers and thunderstorms each afternoon. A gradual improvement on weather conditions is anticipated over the next few days, as a strong surface high pressure moves offshore the eastern coast of the U.S. towards the Central Atlantic. This feature will promote the entrance of a slightly drier airmass into the region. Nonetheless, precipitable water content values should remain within normal seasonal values. In response to the surface high, moderate to fresh northeasterly winds will prevail today through at least Tuesday. Then, shifting from the east on Wednesday. Despite of some drier air across the region, shower development is anticipated every afternoon across portions of the interior and southwestern portions of Puerto Rico. However, rainfall accumulations should be less compared to the previous days. 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. .LONG TERM...Wednesday through Sunday... A more unstable and wetter pattern is expected to evolve during the long term period as a mid-to upper-level trough develops and remains nearly stationary over the west/southwestern Atlantic. By Wednesday, the surface high pressure north of the area is expected to weaken and in response winds are expected to veer from the southeast, and become lighter through the rest of the period. Meanwhile, old frontal boundaries and a restrengthening of the surface low over the north central Atlantic will induce weak troughs or perturbations across the northeastern Caribbean through the end of the workweek. Steering winds will acquire a westerly component and convective development with heavy showers are possible over portions of the eastern interior, San Juan and vicinity and over the USVI, particularly on Thursday and Friday. Having said that and based on the latest guidance, all afternoons through the long term period should be active 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 102-106 degrees on Friday and Saturday before the onset of afternoon convection. && .AVIATION... (06z) TAFS Expect mainly VFR conditions expected to prevail across all terminals through the forecast period. An increase in TSRA/SHRA this aftn may produce brief MVFR cigs across TJPS aft 28/17Z. VCSH expected for the TJSJ//TIST/TISX terminals after 28/13Z. Mountain obsc is expected for the Cordillera Central from 28/13-22z. Breezy conds are expected with winds out of the NE at 12-16 kts, and stronger gusts after 28/13-14Z. && .MARINE... Light to moderate northeast winds will prevail today across the regional waters, locally higher winds are expected due to sea breeze variations across coastal areas. Winds are expected to incrs from moderate to fresh tonight and continue through at least late Tuesday as a surface high pressure moves off the US East Coast. These increasing winds and a northerly swell spreading across the local waters on Monday will further deteriorate seas through at least mid-week. Small Craft Advisories are in effect for the Atlantic waters and the Mona Passage. && .BEACH FORECAST... Short-period waves and onshore flow along the northern and eastern beaches of the islands will promote a moderate risk of rip currents today. A northerly swell arriving on Monday and stronger winds will increase the risk of rip currents and promote life- threatening rip currents from Monday through at least late Wednesday. For more information and details about the latest forecast please refer to the Surf Zone Forecast (SRFSJU). && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...Small Craft Advisory from 6 PM this evening to 6 AM AST Wednesday for AMZ711. Small Craft Advisory from noon Monday to midnight AST Tuesday night for AMZ712-741. && $$ AVIATION/SHORT TERM...GRS MARINE/LONG TERM....13