Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
578 FXCA62 TJSJ 270903 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 503 AM AST Fri Jun 27 2025 .KEY MESSAGES... * A trade wind perturbation will increase the activity of showers today, with a better chance for afternoon thunderstorms. * A tropical wave will approach Puerto Rico and the U.S. Virgin Islands from the eastern Caribbean late Saturday, crossing the islands on Sunday. * An area with slightly drier air and suspended Saharan dust particles will arrive early next week. * Winds and choppy seas will continue to promote life- threatening rip currents across exposed beaches. && .SHORT TERM...Today through Sunday... Tranquil weather conditions persisted overnight across Puerto Rico and the U.S. Virgin Islands, consistent with previous nights. A few brief, light showers moved across northeastern Puerto Rico, producing minimal rainfall accumulations. Winds were generally from the east-northeast at 5 to 15 mph, with stronger gusts near the coast. Temperatures ranged from the upper 70s to low 80s in urban areas and from the 60s to low 70s in mountainous regions. A gradual increase in low-level moisture and precipitable water values, ranging between 1.40 and 1.80 inches, is expected across the region today through Saturday. Forecast guidance continues to indicate the approach of an upper-level trough, which will enhance atmospheric instability, particularly during the afternoon hours, as it interacts with local effects and diurnal heating. These conditions will favor the development of scattered to numerous showers and isolated thunderstorms, mainly over the interior and western sections of Puerto Rico, as well as downwind from the U.S. Virgin Islands. On Sunday, a surge of tropical moisture associated with an approaching tropical wave is anticipated. At this time, Sunday is expected to be the most active and unstable day of the short-term period, with precipitable water values above 2 inches. The highest risk for flooding rains will be from the afternoon into the evening hours, particularly across areas with poor drainage or near steep terrain. Residents and visitors are advised to monitor the forecast in the coming days. .LONG TERM...Monday through Friday... A mid-level ridge will build and hold over the northeast Caribbean by early next week, establishing a strong trade wind inversion that will promote subsidence and a drier atmosphere aloft, significantly limiting deep convective development through midweek. At the same time, a Saharan Air Layer (SAL) arrived behind Sunday`s tropical wave, resulting in hazy skies, degraded air quality, and reduced visibility from Monday through at least Tuesday. Once again, model guidance indicates a tropical wave moving well south across the southern section of the Caribbean, leaving the islands under the influence of pockets of moisture embedded within easterly trade winds. The ridge aloft will weaken around Wednesday as the dry air mass leaves the region, and a retrograding mid- to upper-level trough/low moves closer to the islands, inducing perturbations at the surface. As the trough retrogrades toward the Northeast Caribbean, it will induce perturbations in the surface that will be pushed by the trades at times. However, a tropical wave is expected to arrive, increasing the moisture content by late Thursday night or Friday and transitioning into a more unstable weather pattern. Temperatures are expected to trend above normal, especially under the influence of the SAL, which will reduce overnight cooling and result in warmer minimum and maximum temperatures across the islands. && .AVIATION... (06Z TAFs) VFR conditions across all TAF sites. However, brief MVFR conditions are possible near TJBQ and TJPS after 27/17Z due to VCTS possible. Expect E-NE winds ranging from 8 to 29 kt with occasional higher gusts after 27/13Z and through 27/23Z. && .MARINE... Mariners can expect choppy seas across the local Atlantic and Caribbean waters due to the surface high pressure across the Atlantic, supporting a moderate to fresh easterly wind flow. A trade wind perturbation will arrive today, increasing the potential for showers and thunderstorms, followed by a tropical wave late Saturday night into Sunday. && .BEACH FORECAST... Wind-driven seas will maintain a moderate risk of rip currents along most exposed beaches of the islands today and through much of the forecast period. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...MMC LONG TERM....CAM AVIATION...MMC