Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
266 FXCA62 TJSJ 222000 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 400 PM AST Sun Sep 22 2024 .SYNOPSIS... Fair weather conditions are expected to return a few hours after sunset and continue throughout the night. Showers with isolated thunderstorm activity are likely each afternoon, heightened between Monday and Tuesday due to the proximity of an upper-level trough and increased moisture levels. Excessive heat will continue to pose a risk to vulnerable individuals, particularly those outdoors without proper cooling or hydration. Additionally, the moderate risk of rip currents will return by midweek. && .SHORT TERM...Tonight through Tuesday... Generally fair, warm-to-hot conditions, with skies becoming progressively partly to variably cloudy by midday. Shower with isolated thunderstorm activity began early in the afternoon, spreading from the interior northward into coastal areas of northwestern and northeastern Puerto Rico. So far, radar estimates indicated the highest rainfall totals, around 1.5-2.0 inches, from Gurabo northward across Trujillo Alto and Carolina. Surface observations report consistently hot temperatures up to 92-95F, with heat indices rising into the mid-100s, while higher elevations recorded temperatures in the lower 80s. Winds were predominantly from the east to east-southeast at 5-15 mph, with gusts up to 20 mph along coastal areas. A weak low-level high pressure over the Tropical Atlantic will continue to provide a southerly component in the winds through the rest of the short term period. However, light and variable winds will prevail through at least Monday, influenced by sea/land breezes. A relatively drier air mass is over the area today, as an upper level-low continues to move east over the Leeward Islands and an upper-level ridge extends from the central Caribbean. This will be replaced by an upper-level trough that is moving from the western Atlantic. This will promote troughiness and better moisture content from late Monday through Tuesday. Therefore, showers and thunderstorms will increase in coverage once again, especially on Tuesday afternoon. Weak steering winds will also lead to higher rainfall accumulations over the same areas, increasing the potential for flooding and mudslides in areas of steep terrain. Particularly along the Cordillera Central. Across the USVI, a similar weather pattern is expected to continue during the next few days with diurnally induced afternoon showers developing downwind of the islands. However, for the rest of today and through the night isolated thunderstorms can develop over the waters near the islands due to the proximity of the upper-level low over the Anegada Passage. High temperatures in the upper 80s to low 90s will continue across the lower elevations of the islands during the morning and early afternoon hours across all the islands. Therefore, excessive heat conditions can be anticipated each day. Warm temperatures in the low 80s will continue during the nights across coastal areas. .LONG TERM...Wednesday through Saturday... From previous discussion issued at 504 AM AST Sun Sep 22 2024 For the long term, we anticipate calm and warm weather conditions with the development of showers and thunderstorm activity, particularly in the afternoon hours. On Wednesday, the steering wind flow will gradually recover to around 10-15 knots as the deep-layered trough continues to exit the region. The latest model guidance suggests that all the available moisture should remain below 700 mb through at least Thursday, meaning that patches of moisture will move across the forecast area from time to time, resulting in showers reaching the coastal areas of Puerto Rico and the Virgin Islands each day. The strongest shower and thunderstorm activity is expected each afternoon across the Cordillera Central, with the activity then drifting toward the coast. From Friday into the upcoming weekend, we foresee that a tropical wave will move well south of Puerto Rico and the U.S. Virgin Islands. However, we anticipate a slight increase in moisture across the area, which could enhance shower development. With the proximity of this tropical wave and the everyday afternoon shower activity, we forecast occasional ponding of water on roads and poorly drained areas through Saturday. Temperature-wise, above-normal temperatures are expected to persist over the region, with the threat of excessive heat each day. This heat will mainly impact those without effective cooling, adequate hydration, or prolonged exposure. && .AVIATION... (18Z TAFs) Mainly VFR conditions expected through the forecast period. However, SHRA/TSRA over mainland PR may cause brief MVFR conds at TJSJ/TJBQ thru 22/22z. Mostly VCSH expected at TIST/TISX. Light winds with a southerly component will continue to prevail thru Monday. && .MARINE... A surface low pressure to the northeast of the region over the Central Atlantic will maintain light and variable winds into the early part of next week. Showers and isolated thunderstorms will develop from time to time across the regional waters, and some will move into the coastal waters of Puerto Rico each afternoon. && .BEACH FORECAST... The rip current risk will remain low across the islands through at least Tuesday night, when the moderate risk returns for the northern coastal areas of Puerto Rico. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007- 008-010>013. VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002. AM...None. && $$ SHORT TERM...DSR/RAM LONG TERM....ICP AVIATION...DS/RAM PUBLIC...GRS/ICP