AFDSJU Area Forecast Discussion National Weather Service San Juan PR 257 PM AST Wed Jul 9 2025 .KEY MESSAGES... * Passing showers will continue across the USVI and eastern sections of PR tonight into Thursday morning hours. Diurnally induced afternoon showers and isolated thunderstorms are expected over portions of the Cordillera Central and western PR each day. * Breezy to locally windy conditions will promote choppy seas and a moderate risk of rip currents over the next few days. * Moderate to high concentrations of Saharan dust are expected to return late tonight through at least Sunday, resulting in hazy skies, reduced visibility, and poor air quality. && .SHORT TERM...Tonight through Friday... A wind surge will promote rough seas due to moderate to locally fresh winds across the local waters, accompanied by scattered to numerous showers through at least Thursday morning. Another easterly perturbation will reach the Lesser Antilles late tonight, moving near the US Virgin Islands and Puerto Rico by late Thursday night and early Friday morning. Another pulse of suspended Saharan dust particles will arrive as early as late tonight and persist through the weekend. Overnight, scattered to numerous showers moved across the local waters, with some reaching windward areas of the U.S. Virgin Islands and Puerto Rico. This activity was associated with a wind surge that increased local winds and generated rough seas for mariners. Skies were variably cloudy, with temperatures ranging from the low to mid- 60s in the mountains and valleys to the upper 70s and low 80s in urban coastal areas. A wind surge will bring scattered showers and stronger winds across the region starting today. From Thursday to early Friday morning, a tropical wave accompanied by a band of moisture with precipitable water values ranging from 1.85 to 2.10 inches will move through the area. However, higher concentrations of Saharan dust embedded within the wave may limit overall shower development. As a result, a similar weather pattern is expected each day, with passing showers across the U.S. Virgin Islands and eastern Puerto Rico during the night and early morning, followed by afternoon convection over central and western Puerto Rico and streamer development downwind of the USVI and El Yunque. Localized impacts may include ponding of water on roads, poorly drained areas, as well as urban and small stream flooding, particularly during heavier thunderstorms. Moisture will rapidly erode after Friday morning. Additionally, based on the latest model guidance, an area of suspended Saharan dust particles is forecast to move across Puerto Rico and the U.S. Virgin Islands as early as tonight, continuing through the weekend. This will result in hazy skies, reduced visibility, and deteriorated air quality across the region. Sensitive groups should take precautionary measures, as airborne particulates may impact respiratory health. Recent observations suggested the arrival of a pocket of dry air across the southern slopes resulting in RH drops around the low and mid 50s with sustained winds between 15 mph and higher gusts. .LONG TERM...Saturday through Wednesday... .PREV DISCUSSION... /issued 452 AM AST Wed Jul 9 2025/ The latest model guidance continues to indicate the arrival of Saharan Dust particles along with a notably dry airmass through at least late Sunday. Additionally, mid to upper level dry air and a reinforcing trade wind inversion will further inhibit vertical cloud development, suppressing widespread convection. With this setup, residents and visitors in Puerto Rico and the U.S. Virgin Islands can expect hazy skies, reduced visibility, and potential air quality concerns, particularly for individuals with respiratory conditions. Breezy conditions will prevail through Saturday, with persistent easterly winds supporting above-normal temperatures, especially across coastal and urban areas. By Sunday, a Tropical Upper-Tropospheric Trough (TUTT) is forecast to shift westward toward Hispaniola and linger there through midweek. Beginning Monday, 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. Tuesday currently appears to have the highest rainfall potential as a tropical wave approaches the forecast area, bringing deeper 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... (18Z TAFs) Mainly VFR conds are expected to prevail across all terminals. However, expect diurnally induced afternoon SHRA over the interior and W-PR and downwind from el Yunque, with most of the activity in the VCTY of our terminals. Some SHRA/-SHRA will form near the USVI and E-PR terminals, btwn 10/02-12z. Higher concentrations of Saharan dust return from Thursday onward and visibilities could drop to 5-6 SM. Winds will continue E-ENE at 15-25 kt with higher gusts and sea breeze variations, winds will return around 10 kt aft 09/23z. && .MARINE... A surface high pressure across the Atlantic with promote moderate to fresh easterly winds resulting in Small Craft Advisories across the offshore and onshore Atlantic waters and the Anegada passage through at least Thursday morning and choppy seas across most local waters over the next few days. An easterly perturbation will reach the area tonight, increasing the frequency of showers across the waters. Additionally, another pulse of suspended Saharan dust particles will arrive late tonight and persist through next Sunday resulting in hazy skies and reduced visibility. && .BEACH FORECAST... Breezy to locally windy conditions over the next several days will promote a persistent moderate risk of rip currents across most local beaches of Puerto Rico and the US Virgin Islands. Beachgoers are encouraged to exercise caution as life-threatening rip currents are possible in the surf zone. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...Small Craft Advisory until noon AST Thursday for AMZ711. Small Craft Advisory until midnight AST tonight for AMZ712. Small Craft Advisory until 6 AM AST Thursday for AMZ723. && $$