440 FXCA62 TJSJ 101749 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 149 PM AST Thu Jul 10 2025 .KEY MESSAGES... * Hazy skies and poor air quality due to Saharan dust will persist through the weekend, especially impacting sensitive groups. * Warmer-than-normal nights and hot daytime temperatures will continue, with heat indices reaching levels that may warrant Heat Advisories or Extreme Heat Warningsparticularly in urban and coastal areas. * A moderate risk of rip currents continues along north- and east- facing beaches of Puerto Rico and parts of the U.S. Virgin Islands. && .SHORT TERM...Tonight through Saturday... After the surge of moisture that brought scattered to widespread showers across the islands, a slot of dry air limits rain activity and produces hazy skies. Maximum temperatures were in the low and mid-90s along the urban coastal areas, with warm to hot maximum heat indices. At the same time, the mountain zones observed maximum temperatures between the mid-80s and low 80s degrees Fahrenheit. Winds were from the east to east northeast at 15 to 25 mph, with higher gusts and variations due to sea breezes. Following the passage of todays perturbation, stronger east- southeasterly winds will promote breezy conditions and usher in a much drier air mass, with precipitable water values expected to fall between 1.15 and 1.35 inches. This drier environment will coincide with moderate to high concentrations of Saharan dust, signaling the onset of a hazy, warmer, and more stable weather pattern across Puerto Rico and the US Virgin Islands, expected to prevail through the weekend. At the mid-to-upper levels, a trough located to the northeast of the region will gradually replace the retreating mid-level ridge, settling northwest of the islands by Saturday. However, the extensive mid-level dry air mass will minimize the impacts of this trough aloft by promoting subsidence aloft in the area. Tonight marks a transitional period, with residual afternoon and evening convection across western Puerto Rico giving way to increasingly dry and hazy conditions that will suppress additional shower development. As a result, visibility and air quality will deteriorate, especially for sensitive populations. Fair and dry weather will dominate across the US Virgin Islands and eastern Puerto Rico. Regardless of these conditions, we cannot rule out the possibility of a pocket of moisture arriving, resulting in a few passing showers across the windward locations. Then, diurnal heating and local effects may produce reduced afternoon convection each day. Warmer-than-normal minimum temperatures are expected to return due to this concentration of SAL, which will reduce nighttime cooling. As days begin warmer than normal, maximum temperatures will reach above normal levels, which, combined with the available low-level moisture, will result in warm to hot heat indices. These heat indices may reach levels that prompt Heat Advisories or Extreme Heat Warnings, particularly in urban and lower-elevation areas of Puerto Rico. Residents and visitors, as well as the sensitive communities, are advised to take appropriate precautions during this period, particularly those who are sensitive to reduced air quality and heat. .LONG TERM...Sunday through Thursday...from prev discussion... On Sunday, Saharan Dust concentrations will begin to diminish. However, we still anticipate hazy skies across the U.S. Virgin Islands and Puerto Rico. The latest model guidance continues to indicate a Tropical Upper-Tropospheric Trough (TUTT) shifting westward towards Hispanola and lingering there through the beginning of the workweek weakening the high pressure system at the surface and forcing the breezy to locally windy conditions to diminish. On Monday and Tuesday, the approach of easterly trade wind perturbations will gradually enhance moisture levels across the region. As atmospheric moisture increases, so will the potential for shower and thunderstorm activity, particularly during the afternoon hours over western and southwestern Puerto Rico, with pockets of showers over eastern Puerto Rico in the morning hours. Additionally, model guidance indicate that moisture will extend from the surface through the mid and upper levels of the atmosphere, supporting increased atmospheric instability and enhancing the potential for convective development during this period. By midweek, a tropical wave is expected to approach the forecast area, bringing increased tropical moisture. However, the most intense part of the wave is expected to pass south of Puerto Rico and the U.S. Virgin Islands. Nevertheless, scattered showers and thunderstorms are anticipated each afternoon, especially across interior and western areas. We will continue to monitor conditions closely for any significant changes. && .AVIATION... SHRA will likely form near or over TJBQ btwn thru 10/23Z, possibly causing brief MVFR conds. VCSH are also possible around TJSJ and USVI terminals throughout the period, especially after 10/23Z. We expect hazy skies with visibilities reduced between 5-6SM due to the arrival of moderate to high concentrations of suspended Saharan dust particles. Breezy to locally windy winds of 16-22 kt thru 10-23Z, diminishing to 10-15 kt aft 10/23Z, but returning to similar speeds tomorrow aft 11/13z. && .MARINE... Mariners can expect moderate to fresh easterly winds and choppy seas across the islands through the weekend. An extensive Saharan Air Layer will move across the Northeastern Caribbean lingering through the weekend, and leaving a tropical wave well south of the islands. && .BEACH FORECAST... Moderate to high rip current risk continues along north- and east- facing beaches of Puerto Rico and parts of the USVI. Always swim near lifeguards and obey posted warnings. Conditions may be dangerous for inexperienced swimmers. Expect hot and hazy conditions through the weekend, with excessive heat posing a riskespecially in urban and coastal areas. Heat indices may exceed 108F, so stay hydrated, seek shade, and avoid peak sun hours. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007- 008-010-011. VI...None. AM...None. && $$ SHORT TERM...CAM LONG TERM....YZR AVIATION...YZR
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