Oakland is bracing for possible violence in the wake of...

Oakland is warning residents and merchants to prepare for possible riots when the Missouri grand jury announces its decision over whether a white Ferguson police officer will face charges in the shooting death of a black man.

Oakland Mayor Jean Quan advised Tuesday that anyone living or working downtown should park in a secure, off-street location, move trash cans to a secure site, double-check locks and security cameras, and re-enforce doors with steel plates so they can’t be pried open.

“Although we don’t anticipate problems to occur, keeping peace on our streets and protecting the safety of Oakland residents and businesses is our top priority and we will be prepared,” Quan wrote in a letter to residents and business owners. “We are providing this information to raise awareness about these events, not to alarm, and so that you may plan ahead.”

Several groups plan to converge at Frank Ogawa Plaza near City Hall at 5 p.m. the day the decision is announced, Quan said.

A Missouri grand jury will be deciding whether Ferguson police officer, Darren Wilson, will be charged in the fatal Aug. 9 shooting of 18-year-old Michael Brown. The decision is expected this month, and although it is unknown when it will be made, Missouri Gov. Jay Nixon declared a state of emergency this week in anticipation of possible violence in the wake of the decision.

In Oakland, Frank Ogawa Plaza, located at 14th Street and Broadway downtown, was a gathering place for the Occupy and Oscar Grant protests several years ago, some of which turned violent after nightfall.

Since those protests, Oakland police have reformed the way officers handle crowd control, Quan said. Use-of-force incidents have dropped dramatcally, officers now wear chest-mounted cameras on their uniforms and the department is near compliance wth its court-ordered reforms, she said.

In addition, the city is providing four “healing centers” for people to discuss the verdict: Youth Uprising at 8711 MacArthur Boulevard, Youth Employment Partnership at 2300 International Bvd., and Health Communities/Healthy Oakland at 2580 San Pablo Ave and 1485 8th Street.

Residents and others can get traffic and public safety updates at oaklandnet.com and via Twitter at @Oakland and @Oaklandpoliceca.

Carolyn Jones is a San Francisco Chronicle staff writer. E-mail: carolynjones@sfchronicle.com. Twitter: @carolynajones