833 FXCA62 TJSJ 082350 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 750 PM AST Sun Sep 8 2019 .UPDATE...The potential for afternoon showers and thunderstorms developing over and north of the Cordillera Central and Sierra de Luquillo during the afternoon hours continues. Soils are already saturated, therefore, likely to observe once again urban and small stream flooding as well as rapid river rises and mudslides in areas of steep terrain Monday afternoon. Somewhat drier weather conditions are expected Tuesday onwards. && .AVIATION...VFR conds will continue to prevail at all TAF sites overnight. Aft 09/16z SHRA/TSRA are expected in and around TJSJ/TJBQ and TJMZ resulting in MVFR conds at times through about 09/22z. Light and variable winds overnight. && .MARINE...Although a northerly swell will continue to arrive into the Atlantic waters, seas below 5 feet are still expected. Winds 5 to 10 knots to continue. A moderate risk of rip currents continues along most of the north facing beaches of Puerto Rico, Culebra and Saint Thomas. && .PREV DISCUSSION... /issued 152 PM AST Sun Sep 8 2019/ SYNOPSIS... An upper level trough will continue to bring unstable conditions along the area. This in combination with light steering winds, previous rainfall and local effects will create active weather in the afternoon hours across mainland Puerto Rico. SHORT TERM...Tonight through Tuesday... A few lingering showers could persist through the night hours across the local islands. An upper level trough will persist across the region through the start of the workweek. Although moisture content is expected to be lower than during the weekend, with precipitable water values in the 1.6 to 1.7 inches range, the environment will remain favorable for shower and thunderstorm formation during the afternoon hours due to the instability created by the upper level trough and local effects. The latest GFS sounding shows that the steering flow in the lower 6 km will remain at 5 knots or less, coming out of the south. Since the terrain remains saturated due to the heavy rainfall observed in the past few days, conditions are favorable for urban and small stream flooding, rapid rises of streams and rivers as well as mudslides in areas of steep terrain. Flash flooding will also remain possible in these areas. The higher risk for heavy rain and thunderstorms will be across the interior, northern, eastern and western Puerto Rico. However, additional activity cannot be ruled out elsewhere, including Vieques, Culebra and the U.S. Virgin Islands. The upper level low will cross the local islands on Monday night into Tuesday, to be positioned just north of our area. At the lower levels, conditions will remain fairly similar to Monday. Therefore, another round of afternoon convection with the potential for flooding, rapid rises of rivers and mudslides will continue to prevail. With winds out of the east-southeast, the areas with the better chance to receive heavy showers are once again the interior, western and northwestern Puerto Rico as well as portions of the San Juan metro area. Isolated activity will be possible elsewhere. LONG TERM...Wednesday through Sunday The TUTT will be positioned north of the islands on Wednesday. It is expected to move to the Leeward Islands by late Friday night, wander somewhat and then retreat to the north on Sunday. A weak trough in the lower levels will invade the ridging from the northeast out of the Atlantic to bring some more showers late Thursday. Moisture will increase gradually through Sunday. On Sunday of next week the GFS and the ECMWF show a tropical cyclone moving toward the Leeward Islands. The models have been homing in on a solution that takes the system near the islands by early next week, but this is still highly uncertain and is not fully reflected in the forecast at this time. In any case a passing wave will bring better moisture late in the period. AVIATION...SHRA/TSRA developing across the local flying area. This activity will continue through at least 07/23z. BKN-OVC ceiling are expected over and in the vicinity of TJSJ/TJMZ/TJBQ. JSJ/JBQ had MVFR TEMPO thru at least 21z. Winds from the E-ESE at 10 knots or less with sea breeze variations and higher gusts in TSRA, becoming calm to light and VRB. MARINE... Seas of 5 feet or less are expected to continue across the local area with winds of 5 to 10 knots until the first half of the workweek. However, seas will become hazardous quickly in areas of thunderstorms. There is a moderate risk of rip currents for the northern and northwestern corner of Puerto Rico, as well as for some beaches along Culebra and St. Thomas. && .PRELIMINARY POINT TEMPS/POPS... SJU 78 91 79 91 / 30 30 30 40 STT 79 88 80 90 / 40 30 30 40 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ Aviation...OM Update....OM