000 FXCA62 TJSJ 300133 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 933 PM AST Mon Nov 29 2021 .UPDATE...Similar to what we observed yesterday, afternoon showers and isolated thunderstorms affected mainly the western half of PR. However, an line of showers moved into southwestern PR early in the evening hours, causing some ponding or water in a few areas. The shower activity over land has mostly dissipated and only light rain remains. Consistent with tonight's forecast, the shower activity has mostly moved over the waters and eastern PR. Through the overnight hours, isolated to scattered showers are expected to prevail across the local waters and eastern PR, but not ruling out brief showers across the USVI. The overnight low temps will be in the low to mid 70s across the lower elevations, and in the 60s across the higher elevations. && .AVIATION...VFR conds expected through the forecast period. VCSH is expected through at least 30/03 at TJSJ, but possible at times through the night at TJSJ, TIST, and TISX. Winds will be light and variable overnight, then from the E with sea breeze variations, up to around 10KT. No major hazards expected. && .MARINE...Choppy marine conditions expected as a northeasterly swell invades the local waters. Seas will be up to 6 feet tonight and Tuesday, so small craft operators should exercise caution. There is also a high risk of rip currents for many of the local beaches into at least Wednesday. && .PREV DISCUSSION... /issued 524 PM AST Mon Nov 29 2021/ SYNOPSIS... Afternoon convection over the interior and northwestern sections of Puerto Rico is expected to continue at least for the next few hours. According to Water Vapor satellite imagery, patches of low-level moisture are moving over more of the western part of Puerto Rico. For the rest of the forecast area, a slot of drier air is filtering into the area, limiting the coverage of shower activity. Choppy marine conditions are expected to prevail for the Atlantic offshore waters, as are hazardous coastal conditions. SHORT TERM...Rest of Today through Wednesday... Aloft, a mid-level ridge will hold and continue to build over the region for the short term period. As a result, the coverage of shower activity and intensity will be affected for most of the forecast period. That being said, for the rest of today, the lingering shallow moisture, as suggested by GOES-16 imagery, will continue to result in afternoon activity mainly over the interior and the northwestern sections of Puerto Rico. This shower activity is expected to diminish in the early evening hours. After that, the shower activity is forecast to affect mainly the local waters. However, this activity is expected to be limited, and with minimal rainfall accumulations. On Tuesday, the combination of the stable conditions aloft with the relative lack of moisture will result in mainly fair weather conditions across most of the forecast area, with the typical morning and evening passing showers. Then, in the afternoon hours, there is a somewhat higher chance for development across interior and western Puerto Rico, as another plume of low level moisture is expected to filter into the area. At this time, only ponding of water in roadways and poor drainage areas is likely with this activity due to the influence of the mid level ridge. For the rest of the area, partly cloudy skies are forecast. The best chances for more shower activity starts on late Wednesday, as an easterly perturbation from a deep polar trough is expected to filter into the region. This easterly perturbation will increase the water content over the forecast area. According to model guidance, the bulk of the moisture will be concentrated well south of the forecast area; however, the precipitable water values over the forecast area will fluctuate between 1.5 to 1.8 in. These conditions might provide better chance for development of afternoon shower activity over the interior and western Puerto Rico. LONG TERM....Thursday through Tuesday... PREV DISCUSSION... /issued 411 AM AST Mon Nov 29 2021/ A shortwave trough resulting from a deep polar trough forecast to move across the northwestern Atlantic on Thursday and Friday will briefly weaken the mid and upper-level ridge. However, this shortwave trough will be too far north to have any noticeable effects on the overall weather pattern. Therefore, seasonable weather conditions will continue with some overnight and early morning passing showers across the local waters, with some of the activity moving inland into portions of eastern Puerto Rico and the USVI, followed by afternoon convection across western portions of Puerto Rico. By next weekend, as the shortwave trough lifts well northeast of the area, the mid and upper-level ridge is expected to bounce back again, resulting in stable conditions aloft. Meanwhile, at low-levels, a broad surface high pressure is expected to build north of the area. This will tighten the local pressure gradient and thus will cause an increase in the low-level winds. As a result, a cool advective pattern with an increase in the frequency of trade wind showers is likely, with eastern Puerto Rico and the USVI observing the highest concentration. Some locally induced activity is also possible across western Puerto Rico during the afternoon hours. This cool advective pattern is likely to continue into early next week. Overall, no significant weather features that would result in significant rainfall activity are expected to affect the area during the long-term period. AVIATION...Mainly VFR conditions expected across all local terminals through 30/18Z. However, brief MVFR conditions are possible from SHRA/TSRA at TJBQ through 29/22Z. Then, trade wind SHRA will bring VCSH to TJSJ, USVI and Leeward terminals between 29/22Z and 30/12Z. Winds generally from the ESE at 5-15 knots with sea breeze variations through 29/22Z and once again after 30/12Z, becoming light and variable during the overnight hours. MARINE... A long-dominant-period northerly swell will continue to result in choppy marine conditions for the Atlantic offshore waters at least through early Tuesday. For the rest of the local waters and passages, seas will remain between 3 and 5 feet, with winds up to 15 knots. Improving conditions are expected, in terms of wave height, but hazardous coastal conditions will prevail for the north, east, and northwest coast of all local islands. There is a high risk of rip current for all the north exposed beaches of the forecast area until late mid week. However, according to the latest model guidance, the risk could prevail through the end of the workweek. && .PRELIMINARY POINT TEMPS/POPS... SJU 76 87 75 87 / 20 30 40 20 STT 75 87 76 86 / 10 40 40 20 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through late Wednesday night for Culebra- Mayaguez and Vicinity-North Central-Northeast-Northwest-San Juan and Vicinity-Southeast-Vieques. VI...High Rip Current Risk through late Wednesday night for St Croix- St.Thomas...St. John...and Adjacent Islands. AM...None. && $$ SHORT TERM...JA LONG TERM....LIS PUBLIC DESK...JA