725 FXCA62 TJSJ 301743 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 143 PM AST Mon Jun 30 2025 .KEY MESSAGES... * Moderate concentrations of Saharan Dust through early Tuesday. Another plume of Saharan Dust can reach the region to end the week. * Breezy winds will sustain choppy seas and maintain a moderate risk of rip currents along exposed beaches through midweek. * Another tropical wave is forecast to affect the islands on Friday, again increasing shower and thunderstorm activity. && .SHORT TERM...Tonight through Wednesday... Calm and stable weather dominated the region today. Skies were hazy due to moderate concentrations of Saharan dust. Daytime highs reached the upper 80s to low 90s along the coasts, while mountain areas remained in the upper 70s to low 80s. Winds were from the east at 9 to 25 mph, with the strongest observed along coastal areas. Dry and stable conditions will persist tonight into Tuesday, under the influence of a mid-level ridge and a strong surface high- pressure system over the central Atlantic. These features will continue to support breezy easterly winds, and limited shower activity across the region. A weak surface disturbance is forecast to approach the region late Tuesday night into Wednesday, bringing occasional patches of moisture embedded in the trade winds. This could lead to slightly increased cloud cover and isolated showers from time to time. The mid-level ridge will begin to weaken as a mid-to-upper-level low deepens to the northeast. Although this change may allow for some vertical development, mid-level humidity will remain below average, which may limit more widespread convection. Nonetheless, marginal instability and available moisture could trigger a few isolated showers mainly over western Puerto Rico during the afternoon. .LONG TERM...Thursday through Monday... Although Thursday will start with below normal concentrations of precipitable water (PWAT), peripheral moisture from an approaching tropical wave will increase PWAT to around 1.8 inches by Thursday afternoon and evening. A surface high over the Atlantic will promote up to breezy east to east-southeast steering flow through Saturday, backing thereafter. The diurnal shower pattern will be limited for most of Thursday, with passing morning showers and afternoon showers and stronger showers over western PR. Available moisture will remain below 850 mb on Thursday. However, deeper moisture will reach the area on Friday as PWAT values increase to 2 inches or more. Therefore, Friday is expected to be the wettest day, as a tropical wave crosses the islands and a retrograding mid- to upper-level low also approaches. This will promote a boost in the diurnal pattern and overall increased shower and t-storm activity over the region, a limited to elevated flooding risk will remain. Galvez-Davidson Index (GDI) values are forecasted to reach +45 on Friday, meaning that thunderstorm and heavy rainfall potential will remain. PWAT values will quickly drop to below normal by Saturday before bouncing back to around 1.8 in by Sunday through Monday as moisture remains of the wave are circled back towards the islands by the surface high. The mid- to upper- level low will continue to be near the islands during the weekend and into early next week, promoting some instability. 925 mb temperatures will be above normal with a limited to possibly elevated heat risk each afternoon. The presence of saharan dust, increasing as the period continues, can also serve to limit nighttime cooling. This saharan dust can also serve as a limiting factor for Friday`s tropical wave. && .AVIATION... (18Z TAFS) VFR conditions expected across all TAF sites during the next 24 hours. Moderate concentrations of Saharan dust will result in HZ, with visibility occasionally reduced to 6 SM. E winds will prevail, decreasing to 7 to 12kts after 30/23Z. && .MARINE... Mariners can expect choppy seas across the local Atlantic and Caribbean waters due persistent moderate to fresh easterly winds. Small Craft Should Exercise Caution over most local waters. A mass of drier air with suspended Saharan Dust Particles will continue to filter into the area, maintaining hazy skies through early Tuesday. A tropical wave is forecast to move over the local waters on Friday, increasing shower and thunderstorm chances. && .BEACH FORECAST... A moderate risk of rip currents (life-threatening rip currents are possible in the surf zone) will be in effect for most northern, southern and eastern beaches of Puerto Rico, as well as for beaches of Culebra, Vieques, southern St. John, southern St. Thomas and all but western St. Croix. Although other areas have a low risk of rip currents, keep in mind that life- threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. The low risk of risk of rip currents will spread tomorrow to St. Thomas and St. John. Up to a moderate risk of rip currents will remain for most of the period && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM/MARINE/BEACH FORECAST...MMC LONG TERM...MRR AVIATION...DSR/MMC
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