Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
042 FXCA62 TJSJ 090930 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 530 AM AST Sun Jun 9 2024 .SYNOPSIS...High pressure extends out of the central Atlantic and across the Atlantic waters just north of the local area. With limited moisture this is bringing warmer than usual temperatures that will gradually cool through Friday. Some limited showers will be possible, with a tropical wave passing to our south and moisture from an old frontal boundary entering into the area on Thursday. && .SHORT TERM...Today through Tuesday... An overnight radar and satellite imagery analysis indicated areas of clear to partly cloudy skies as some high clouds moved across the region. Some showers generated variable cloudy skies and rainfall accumulations of up to a tenth of an inch across portions of eastern Puerto Rico, Vieques, and the local waters. Overnight minimum temperatures stayed in the lower 80s across coastal areas of the metro area, northeastern, and southwestern Puerto Rico. Across the mountains, temperatures dropped to the upper 60s. Today we are expecting another day with warm to hot temperatures. Note that an Excessive Heat Warning (NPWSJU) is in effect today for the lower elevations and coastal areas of mainland PR, while eastern PR, Culebra, Vieques, St Croix, St Thomas, and St John have a Heat Advisory. An Excessive Heat Watch is also in effect for Monday, between 9 AM AST and 6 PM AST, as hot conditions will likely return. The general weather pattern will continue to be dominated today by the presence of a ridge at the mid to upper levels and a surface high pressure extending from the eastern Atlantic to the Central Atlantic. This will continue to provide subsidence, inducing stable weather conditions and drier air aloft, mostly resulting in a drying pattern with minimal to no rain activity. The latest Precipitable Water (PW) models suggest values around normal to below normal climatological levels, around 1.5 to 1.9 inches during the short-term period. Tonight into Monday, model guidance continues to suggest the passage of a tropical wave well south of the islands, leaving the bulk of the moisture over the Caribbean Sea. As a result, every day of the period, isolated to scattered afternoon convection may occur due to local effects, especially across northwestern Puerto Rico during the afternoon hours. Furthermore, patches of clouds moving in along the windward areas may bring brief passing showers. Also, due to the warm sea surface temperatures, nighttime showers may form over the adjacent waters and occasionally move inland like the last few days. .LONG TERM...Wednesday through Sunday... A tropical wave will pass just south of the area Tuesday night and Wednesday and will be enhanced somewhat by the passage of a weak upper level trough to the north Tuesday night. Then high pressure aloft intensifies over the Western Caribbean and pushes the remnants of an old frontal boundary into the area from the northeast with its accompanying moisture. Temperatures will rebound on Saturday as surface winds return to a southeasterly flow. Thunderstorms will again become possible Wednesday and Friday over portions of the area and especially the western interior. The influx of Saharan dust will continue through the period bringing hazy skies and visibilities of 8 to 15 miles. && .AVIATION... (06Z TAFs) Mainly VFR conditions prevail across all terminals during the period although TJNR will have some MVFR in the morning. TJBQ may experience some VCSH around 18Z. Light to calm and variable winds will turn from the E-ESE at 10-15 knots between 09/13-22Z, accompanied by higher gusts and sea breeze variations. && .MARINE...Seas will generally run 2 to 4 feet in the open waters around the island and less than 2 feet in protected waters. The wave passage on Tuesday night will boost seas up to 6 feet in the southwest corner of the forecast area. && .CLIMATE...Very warm temperatures have continued with the high of 95 and the low of 81 on Sunday both being the second warmest on record. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Excessive Heat Warning from 9 AM this morning to 6 PM AST this evening for PRZ001-003-005-007-008-010-011. Excessive Heat Watch from Monday morning through Monday afternoon for PRZ001-003-005-007-008-010>013. Heat Advisory from 9 AM this morning to 6 PM AST this evening for PRZ002-012-013. VI...Excessive Heat Watch from Monday morning through Monday afternoon for VIZ001-002. Heat Advisory from 9 AM this morning to 6 PM AST this evening for VIZ001-002. AM...None. && $$ SHORT TERM...YZR LONG TERM....WS AVIATION...YZR