510 FXCA62 TJSJ 082025 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 425 PM AST Fri Oct 8 2021 .SYNOPSIS... Hazy skies due to Saharan dust are expected to continue into tomorrow, then this particulate will gradually diminish. Unsettled weather conditions are expected to begin late Sunday, continuing into the workweek. Therefore, an increase in shower and thunderstorm activity is anticipated. && .SHORT TERM...Tonight through Sunday... Hazy skies due to Saharan dust will continue to linger across the islands through at least the late morning or early afternoon hours on Saturday, but then this particulate will gradually diminish. Additionally, a tropical wave moving over the eastern Caribbean is bringing cloudiness in the upper levels of the atmosphere. As the wave moves away and with the reduction in Saharan dust, visibilities will begin to improve. For the overnight hours, the high resolution models show a few showers moving over eastern/southeastern Puerto Rico with light to moderate rainfall accumulation. For Saturday and early Sunday, a mid level ridge will maintain stable and generally dry conditions for the region. Precipitable water values are expected to be around 1.2 to 1.5 inches, which is below the climatological value. Regardless, small patches of moisture dragged by the trade winds may move from time to time. This, in combination with local effects, may trigger scattered showers and isolated thunderstorms, mainly for the interior and northwestern quadrant of Puerto Rico. By late Sunday, moisture is expected to increase as a tropical wave approaches the region. Therefore, showers will gradually increase in frequency across eastern sections of Puerto Rico and the U.S. Virgin Islands, continuing into the long-term portion of the forecast. .LONG TERM...Monday through Saturday.../from prev discussion/ A wet weather pattern continues to appear likely during the long- term period. On Monday, a vigorous tropical wave will move over the area. This will result in widespread shower and thunderstorm activity, with activity concentrated across eastern Puerto Rico and the USVI during the morning hours followed by enhanced convective activity over mainland Puerto Rico during the afternoon hours. By Tuesday, a mid and upper-level trough will become cutoff and amplify over Cuba, inducing a broad low-level trough north of Hispanola. This feature will induce a deep southerly flow, tapping deep tropical moisture from the Intertropical Convergence Zone (ITCZ) into the local area. This overall pattern is expected to prevail through the rest of the long term period, helping to support a moist and unstable air mass. In fact, model guidance suggests precipitable water values fluctuating between 2.1 and 2.5 inches during the period, which are between the 75th to 99th percentile for this time of the year. Therefore, conditions at this time appear favorable for deep and organized convective activity to develop and affect the local area with the potential for portions of the area to observe significant rainfall activity with an enhanced threat for flooding and mudslides. Given that this potential rainy pattern is still in the long term period, there are still some uncertainties in the overall details of where the heaviest rainfall activity will occur and how significant it will be. && .AVIATION...VFR conditions will continue through the forecast period. Visibilities are reduced due to the presence of Saharan Dust. VIS have ranged between 3-6 SM in PR/USVI, with lower VIS in TNCM/TKPK. SHRA possible near TJBQ and TJMZ between 19Z-22Z. Winds will remain from the east at 10-20 kts, becoming light and variable overnight. && .MARINE... Seas up to 5 feet with winds up to 15 knots are expected to continue today. For tomorrow and through the weekend, a northerly swell will invade the local waters, resulting in choppy seas up to 6 feet. For the beaches, there is a moderate rip current risk for northern, eastern and southeastern Puerto Rico, some beaches in Vieques and Culebra, northwestern St. Thomas and the eastern third of St. Croix. && .PRELIMINARY POINT TEMPS/POPS... SJU 78 90 77 90 / 10 20 20 30 STT 79 89 78 90 / 20 20 20 30 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk from Saturday morning through Sunday afternoon for North Central-Northwest-San Juan and Vicinity. VI...None. AM...None. && $$ SHORT TERM...CAM LONG TERM....ERG PUBLIC DESK...CVB