871 FXCA62 TJSJ 211524 AAA AFDSJU Area Forecast Discussion...UPDATED National Weather Service San Juan PR 1124 AM AST Sat Aug 21 2021 .UPDATE...Hazy conditions have arrived and several stations in the area are reporting between 5 and 7 miles visibility in Saharan dust. Winds and temperatures are similar to yesterday, but so far only isolated light showers are present. Still expect showers to develop in west northwest Puerto Rico and move offshore with a slight chance of a thunderstorm developing there. Little change to the forecast package or overall reasoning. && .AVIATION...VFR conds expected across the local terminals through the forecast period with HZ due to Saharan dust. Winds will be up to around 15 KT gusting to 25 KT from the E with sea breeze variations developing after 21/14Z.VCSH/VCTS possible at TJBQ after 21/17Z. Winds will decrease after 21/23Z, but return slightly stronger aft 22/12Z. && .MARINE...Models continue to show a wind surge after the southerly passage of a tropical wave. No longer expect thunderstorms tonight or tomorrow in the local southern outer Caribbean waters due to dust episode and strong capping near 6800 feet. Models continue to bring in 7 foot seas into the outer waters and the western inner local Atlantic waters due to local winds, so small craft advisories have been added. Since the event will likely diminish by Monday afternoon, have not extended the current advisory, but will reconsider later should indications that winds will not diminish soon enough. && .PREV DISCUSSION... /issued 417 AM AST Sat Aug 21 2021/ SYNOPSIS... Mainly fair weather conditions are expected to prevail today as a slightly drier airmass with Saharan dust continues to filter into the region. However, scattered showers with a few isolated thunderstorm are forecast over the northwestern quadrant of Puerto Rico this afternoon. For tomorrow, a slight increase in shower activity are expected, as a tropical wave moves into the area and combines with a upper level trough, resulting in afternoon convection over the western sections of Puerto Rico. Choppy to hazardous marine conditions will prevail for the next several days. SHORT TERM...Today through Monday... Mainly warm to hot temperatures are expected for the next few days, with haze due to Saharan dust. The Saharan dust will be in higher concentrations today compared to what is expected on Sunday and Monday. Mainly fair weather will be expected today and Monday, but a chance of showers and isolated thunderstorms is forecast for this afternoon across western PR, as near normal moisture combines with a strengthening TUTT to our north, local sea breeze convergence and diurnal heating. However, Monday afternoon should remain dry through the day as a very strong trade wind inversion could develop and the mid levels are expected to be rather dry, on top of below normal precipitable water. A higher chance of rain is forecast for Sunday, making Sunday the wettest day of the short term period, though the model guidance is backing off on the amounts of rain expected. The increase in chances of rain for Sunday is due to a tropical wave passing south of the local area, causing moisture to increase and bringing scattered showers across eastern PR and the USVI, while western PR could have thunderstorms in the afternoon hours. Surface high pressure across the west central Atlantic will promote easterly winds that could be between 10 and 20 mph across the local islands, and winds up to 20 knots or slightly higher possible across the local waters. Daytime high temperatures are expected to be similar to yesterday, around the upper 80s to lower 90s across the lower elevations and the upper 70s to mid 80s in higher elevations. The heat index values could be in the 100 to 105 degree range across coastal areas, especially across the north coastal areas. LONG TERM... Tuesday through Saturday... A dry pattern is expected for the long term forecast period across the local region. Model guidance continues to suggest a mid- upper level ridge located just north of the forecast area, promoting stable conditions. Meanwhile, at the surface, a drier air mass with Saharan dust particles is expected to filter into the region on Tuesday into Thursday. Given the expected conditions, a dry weather pattern and hazy skies can be expected for most of the upcoming week with minimal precipitation forecast over western Puerto Rico, due to the local effects. On Friday, a slight increase in moisture is expected over the local area as a weak tropical wave passes over the area. The moisture increase with a southeasterly wind flow will result in shower activity over the northwestern quadrant of Puerto Rico on Friday afternoon. By Saturday, fair weather conditions are anticipated once again as precipitable water values drop below normal and a mid to upper level ridge promotes stable conditions. AVIATION...VFR conds expected across the local terminals through the forecast period with HZ due to Saharan dust. Winds will be up to around 15KT gusting to 25KT from the E with sea breeze variations at TJPS developing after 21/14Z. VIS could be very close to 6SM due to HZ, but will keep P6SM until observations confirm the obstruction in VIS, which we will monitor closely. VCSH/VCTS possible at TJBQ after 21/17Z. Winds will decrease after 21/23Z. MARINE... A surface high pressure will continue to result in a moderate to fresh easterly winds over the forecast area during the next several days. Therefore, choppy seas up to 6 feet are expected across the regional waters through Saturday. A tropical wave is expected to move over the region on Sunday into Monday, which will cause an increase in seas, becoming hazardous. While isolated to scattered showers over the local waters are also expected with this tropical wave. There is small craft advisory for the Atlantic offshore waters, which will go into effect on Sunday morning. && .PRELIMINARY POINT TEMPS/POPS... SJU 90 81 87 80 / 20 30 20 20 STT 90 80 90 80 / 20 20 10 10 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...VI...None. AM...Small Craft Advisory from 8 AM Sunday to 6 AM AST Monday for Coastal Waters of Northern Puerto Rico out 10 NM. Small Craft Advisory from 8 AM Sunday to 8 PM AST Monday for Atlantic Waters of Puerto Rico and USVI from 10 NM to 19.5N- Mona Passage Southward to 17N. Small Craft Advisory from 8 PM Sunday to 8 PM AST Monday for Caribbean Waters of Puerto Rico from 10 NM to 17N. && $$ SHORT TERM...OM LONG TERM....WS PUBLIC DESK...TW