436 FXCA62 TJSJ 311911 CCA AFDSJU Area Forecast Discussion...CORRECTED National Weather Service San Juan PR 311 PM AST Sat May 31 2025 .KEY MESSAGES... * An extensive and dense plume of Saharan Air Layer (SAL) will affect the local islands through midweek next week. * Warmer than normal temperatures are likely to continue during the next few days across most coastal and lower elevations of the islands. * An increase in surface winds will induce some moderate to locally fresh winds, resulting in wind-driven seas. Therefore, small craft operators should exercise caution. && .SHORT TERM...Tonight through Monday... The mid to upper level cloud deck that affected the islands during the past couple of days has mostly moved away towards our east, however some mid to upper level cloudiness has remained. These cloud decks are mainly due a disturbance over South America and an upper trough, that is now well north of the local islands. However, another trough is moving in from our west and should linger through the weekend. A mid-level ridge is also present and will remain nearly stationary over the region during the period and will continue to support a trade wind inversion (detected by the 12Z sounding), effectively suppressing deep convective development across Puerto Rico and the U.S. Virgin Islands. This pattern is forecast to continue with drier air in the mid levels, as a Saharan Air Layer (SAL) also moves in, cutting off moist air in the upper levels and maintaining low level moisture below 800mb. Precipitable water (PWAT) will be at seasonal values during the period, gradually decreasing today and tomorrow. A wind surge will also cross the region from today into Sunday and will increase moisture advection towards windward sectors while another increase in winds is forecast late in the period and into the long term forecast period. In general up to breezy east to east-southeast winds will continue due to a surface high over the Atlantic. A dense Saharan Air Layer (SAL) is soon to arrive, its bulk is currently reaching the Windward and Leeward Islands, and it`s leading edge is filtering into the local islands. Current model guidance continues to indicate that the bulk of this SAL will move into the area this evening from the east/southeast, further deteriorating air quality and resulting in hazy skies, drier air aloft, lower visibilities and adverse conditions for immunocompromised, vulnerable and sensitive groups. This is a moderate to high SAL event, please follow your doctor`s and your Health Department`s recommendations. Despite the Saharan Dust and accompanying dry air, above mentioned instability and diurnal heating can continue to promote shower and isolated thunderstorm development, with afternoon activity concentrating over NW PR and downwind of El Yunque and the local islands. Overnight and morning trade wind showers will also continue over windward sectors of the islands. Breezy east- to- east-southeast winds will continue to promote a limited to elevated heat threat for urban and coastal areas, the presence of Saharan Dust and the absence of the mid to upper level cloud deck that was over the islands during the next few days will also contribute to this heat threat. Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors. Take extra precautions when outside. Wear lightweight and loose fitting clothing. Try to limit strenuous activities to early morning or evening. Take action when you see symptoms of heat exhaustion and heat stroke. Please refer to the latest Hazardous Weather Outlook (HWOSJU) and it`s graphical format (weather.gov/erh/ghwo?wfo=sju) for more information. .LONG TERM...Tuesday trough Saturday...From Prev Discussion... The long-term forecast remains on track. According to the NASA Goddard Earth Observing System Model V5, a dense plume of Saharan Air Layer (SAL) will continue to affect the northeastern Caribbean through midweek. The model indicates that the highest concentrations are expected early in the period, with aerosol optical thickness values nearing 0.5. This pattern will result in hazy skies, reduced visibilities, and deteriorated air quality through at least Wednesday. Although the most intense dust presence is forecast for the first part of the week, low to moderate concentrations are expected to linger into the upcoming weekend. Residents and visitors, particularly those with respiratory conditions, are advised to take appropriate health precautions during this period. At the surface, a high-pressure system will promote southeasterly winds through Tuesday, gradually shifting from the east as the high moves into the central Atlantic. A mid- to upper-level ridge is forecast to strengthen over the region during the early part of the week, favoring a drier and more stable environment aloft. Precipitable water values will remain below climatological normals, near or below 1.5 inches, limiting overall shower activity across the area. However, locally induced showers and isolated thunderstorms remain possible each afternoon across western Puerto Rico, due to diurnal heating and local effects. Temperatures will remain above normal, with highs ranging from the upper 80s to low 90s Fahrenheit in coastal and urban areas, and in the low 80s across higher elevations. Heat indices may exceed 108F during the peak of the event, particularly across north-central Puerto Rico. These hot and dry conditions, combined with poor air quality, could pose additional health risks, especially for the more vulnerable populations. && .AVIATION... (18Z TAFs) Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, brief SHRA/TSRA this afternoon may cause tempo MVFR cigs at TJBQ/TJSJ thru 31/22z. The 31/12z TJSJ sounding indicated ESE winds up to 19 kt blo FL100. HZ due to Saharan dust will gradually move across the local area tonight, and linger through at least early Wednesday. VSBY could drop to around 6SM during the next few days. && .MARINE... A surface high pressure building over the Atlantic Basin will continue to promote moderate to locally fresh trade winds over the next few days. Southeast winds will prevail through the weekend, becoming more easterly early next week. Small craft should exercise caution across portions of the offshore waters and local Caribbean passages. Hazy skies and reduced visibilities are expected through mid-week as another dense plume of Saharan dust moves toward the area. && .BEACH FORECAST... A moderate risk of rip currents will continue across the south to southeast beaches of the islands through the rest of the weekend. Elsewhere, the risk remains low. Nonetheless, swimmers are urged to use caution, especially near piers, reefs, and other structures where dangerous rip currents are more likely to form unexpectedly. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 4 PM AST this afternoon for PRZ001-005-008- 010. VI...None. AM...None. && $$ SHORT TERM...MRR LONG TERM...LIS AVIATION/MARINE/BEACH...DSR
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