New Jersey's primary is tomorrow and voter turnout is expected to be light, except for two close congressional races in the northern part of the state.

One key race to watch is in the 10th district, to replace Congressman Donald Payne, Sr. who passed away earlier this year.  His son Donald Payne Jr. hopes to take that seat.  He's being challenged by Newark City Councilman Ron Rice, state Senator Nia Gill, Irvington Mayor Wayne Smith, two others, Cathy Wright of Newark and Dennis Flynn of Glen Ridge are also vying for the Democratic nomination.

Voters in the 10th district will also choose someone to represent them for the remainder of Payne's term, which ends in January.

"There are a number of high-profile politicians in this race, all of them African American and they are looking to replace the only African American in New Jersey's delegation," said Patrick Murray, political scientist at the Monmouth University Polling Institute.   "This race is a lot closer than a lot of people expect."

The hallmark event for New Jersey's primary is in the 9th district, where two well-known Democratic incumbents Bill Pascrell and Steve Rothman are pitted against each other.

Murray says there is one wild card in this race.

"And that's Bill Clinton.  The former U.S. President has made a campaign stop on behalf of Bill Pascrell, he's endorsed Bill Pascrell and in a race that's as tight as this, an endorsement from a former President could mean the difference.  President Barack Obama has lent his support to Rothman."

He said this will also be a close race.  "This has been a big battle with a lot of debates, a lot of money and a lot of name recognition so it will be interesting to see what happens."

At the top of the ticket, New Jerseyans will cast ballots for their party's nominee for president in what is essentially a moot vote. Obama is unchallenged on the Democratic side. Mitt Romney, who has secured the support needed to be the Republican nominee, faces three challengers who have withdrawn from the race but whose names still appear on the ballot: Newt Gingrich, Ron Paul and Rick Santorum.

Voters will choose a U.S. senator in November, and primary voters will set up that contest. The fall matchup is all but certain to pit Sen. Bob Menendez, the incumbent Democrat, against GOP challenger Joe Kyrillos, who has served in the New Jersey Legislature for 24 years.

Menendez, 58, seeking his second six-year term, is running unopposed in the primary. Kyrillos, 52, who Gov. Chris Christie has endorsed, faces three unknown challengers, none of whom had more than $9,000 on hand for the race.

Voter turnout will be light, around 20% of New Jersey voters will show up at the polls said Murray.

(The Associated Press contributed to this report)