107 FXCA62 TJSJ 172015 AAC AFDSJU Area Forecast Discussion...UPDATED National Weather Service San Juan PR 415 PM AST Fri Jul 17 2020 .SYNOPSIS... An upper level trough will continue promoting instability aloft. The moisture associated with an easterly perturbation will linger over the local islands through Sunday. This will increase the potential for showers and thunderstorms each afternoon. A more seasonal weather pattern is expected through much of the workweek. Another tropical wave will make its way in by the end of next week, thus promoting widespread showers across the region. Tranquil marine conditions will prevail for the next several days. && .SHORT TERM...Tonight through Sunday... Latest satellite-derived precipitable water products is showing an area of drier air advancing into the area, with values ranging around 1.2 to 1.3 inches. This should result in a reduction in the frequency of passing showers over the area, but some of them will still reach portions of eastern Puerto Rico and the U.S. Virgin Islands through the early morning hours. An upper level trough located to the northwest of the islands will increase instability across the area through the weekend. At the mid to lower levels, there is an easterly perturbation that will be advancing to the area on Saturday with a well defined circulation at 700 mb. Currently, this system is embedded within a dry air mass along with Saharan dust. However, the guidance are suggesting that the feature will drag some moisture from the north over the area. This will result in the development of showers over the Atlantic waters that could advance over the northern coast of Puerto Rico through the day. Additionally, this advection of moisture, aided by the upper level trough, should result in the development of showers and thunderstorms during the afternoon hours. The heaviest convection should be focus over the interior and western Puerto Rico, but additional activity could stream from the U.S. Virgin Islands and eastern Puerto Rico. As the perturbation moves toward Hispaniola late Saturday, an east- southeast wind flow will be established. A pocket of drier air is expected to filter in later in the day, but this is expected to be short-lived as additional areas of moisture are expected to be dragged in from time to time, resulting in additional shower activity for Sunday. .LONG TERM...Monday through Friday...From Prev. Discussion... As the upper-level trough weakens, the dynamic forcing will dissipate over the islands. However, plenty of tropical moisture will linger across the region, promoting the typical passing showers across the U.S. Virgin Islands and eastern Puerto Rico, with daytime convection to then gradually increase over the interior and western sections. This pattern will hold throughout the long-term period. Another tropical wave is forecast to reach the islands by the end of the next work-week, between Thursday or Friday. GFS continues suggesting an east-southeast wind flow, which will result in warm to hot temperatures with heat indices above 100 degrees Fahrenheit at least the first half of next week. && .AVIATION... SHRA/TSRA have developed across western PR and are affecting terminal sites TJBQ and TJMZ. Brief MVFR conds are possible due to the SHRA/TSRA this afternoon. This activity will persist until 18/02Z. E PR and the USVI SCT/ISO SHRA are possible through 180/01Z. SCT TO BKN clouds from SCT-BKN between FL020-040. Winds are from the E at 15 to 20 kts with higher gusts. Winds are will fall to 10 to 15 kts by 18/05z. && .MARINE... Tranquil marine conditions are expected for the next few days as seas remain between 2 and 5 feet across the local waters. A surface high pressure just north of the region will maintain winds up to 15 knots from the east. However, local effects will increase winds between 15 and 20 knots at times. There is a moderate risk of rip currents across the northern beaches of Puerto Rico as well as the beaches of eastern Vieques, Culebra and St Croix. && .PRELIMINARY POINT TEMPS/POPS... SJU 78 88 78 89 / 20 30 30 30 STT 79 88 78 90 / 20 30 50 50 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...DS LONG TERM....FRG PUBLIC DESK...FRG