He just held a news conference.

He could have appointed someone to serve until 2014. Instead, the election will be October 16, 2014. The primaries will be August 13.

He would not comment on who he would appoint to serve until then.

I don’t understand all the nuances of NJ politics, so hopefully readers can add local color in the comments.

Update: Not sure if this is right, but supposedly Christie put himself first, via National Journal:

Republicans are fuming over New Jersey Gov. Chris Christie’s decision to hold an early special election to fill the seat of the late Sen. Frank Lautenberg, with several Washington-based operatives suggesting he’s putting his own interests ahead of the GOP’s. The decision to hold a separate special election in October 2013—just two weeks before his own election—would give any interested Republican candidates little time to announce, organize a campaign, and raise the necessary money to take on a top-tier Democrat, likely Newark Mayor Cory Booker….

Christie acknowledged he was legally able to schedule a special election in November 2014, but he wanted New Jersey voters to elect their senator as soon as possible. Christie was less clear about whether he was legally allowed to schedule an election to coincide with his own….

The governor’s decision, along with growing GOP expectations that his appointee will be a placeholder, means that the GOP’s chance at a pickup now looks like a long shot. But Christie protected his own interests by scheduling a separate 2013 election, ensuring that Booker wouldn’t usher a surge of Democratic voters that could hurt Christie’s November prospects.

That did little to mollify Republicans with a stake in retaking the Senate next year. While none wanted to be quoted publicly, all dripped with disdain for Christie’s decision, calling it self-serving.