For the first time since flooding problems began in January, the San Joaquin River on Saturday was expected to reach "danger" stage at Vernalis.

With an "intense" atmospheric river storm aimed at California starting tonight, the San Joaquin County Office of Emergency Services warned residents in the area southwest of Manteca to be prepared to evacuate should a levee break.

Specifically, their recommendation applies to those west of Union Road, south of Nile Road, and north and east of the river.

On the west side of the river, officials recommended that residents between the river and Kasson Road be prepared to evacuate, including the roughly 400 homes at the private San Joaquin River Club where water was seeping through a small hole in the levee even last week.

The San Joaquin may reach "danger" stage even before possible spilling at upstream Don Pedro Reservoir, east of Modesto. If Don Pedro reaches capacity during the coming storm and does spill, however, it would take days for the extra water to reach Vernalis, and it is unclear exactly how much higher the river might go as a result.

In northern San Joaquin County, residents in low-lying Lodi neighborhoods should also be aware. Camanche Dam, upstream of Lodi, may spill over early next week, though a representative with the East Bay Municipal Utility District said on Friday that officials will try to keep flows in the Mokelumne River steady at about 5,000 cubic feet per second.

Sandbags will be available for Lodi residents from 7 a.m. to 7 p.m. today at 1331 S. Ham Lane (bring your own shovel).

The incoming storm is severe enough, the National Weather Service warned on Saturday, that even areas that have not seen flooding in many years may be affected.

— Contact reporter Alex Breitler at (209) 546-8295 or abreitler@recordnet.com. Follow him at recordnet.com/breitlerblog and on Twitter @alexbreitler.