On Tuesday, voters will head to the polls for the special-election primary to fill the state’s vacated U.S. Senate seat. But experts predict that turnout will be low in the election to pick between either party-line-Democrat Edward J. Markey and his underdog, more moderate challenger Stephen F. Lynch, or a diverse slate of Republican hopefuls.

If all goes as predicted by pollsters and pundits, Markey, a 37-year veteran of the House of Representatives, will defeat Rep. Lynch of South Boston. Markey has raised over three times more in campaign funds and has also secured the endorsements of a host of leading Democrats, including the former senior Senator from Massachusetts, John F. Kerry, whose appointment as Secretary of State vacated the contested seat.

After Massachusetts Secretary of State William F. Galvin estimated on Monday that about 120,000 fewer voters would cast ballots in this Democratic primary than did in the 2009 special election primary for senate, Daniel B. Payne, a Democratic media consultant who has worked for Markey, said that the conditions seemed to favor the longtime congressman from Malden.

“In a low turnout election, the core of the Massachusetts Democrats are going to be the ones who turnout,” Payne said Monday afternoon. “[Low turnout] helps Ed Markey because Ed Markey has been organizing since February, and he’s going to have 5,000 people working for him tomorrow.”

Andrew Zucker, a spokesperson for Markey, was also optimistic about Markey’s prospects.

“We’re confident in our grassroots field operation,” he wrote in an email. “It’s the strongest by far of any campaign in this state.” Zucker added that 9,000 volunteers were active in the Markey campaign.

Lynch, who was off the campaign trail due to illness for most of Monday, had been campaigning at a breakneck pace for the last week of the race. The campaigns had shuttered down after the bombings on Marathon Monday, but largely restarted after the alleged bombers were apprehended.

Though recent polls have shown him trailing Markey by about 10 points, Lynch, whose supporter base is seen as solid and dependable, predicted a narrow victory last week after a debate in Springfield.

Payne said that in order for Lynch to pull off the upset, he will need an extremely high turnout in and around his South Boston voter-base, and will also need to keep pace with Markey in affluent suburbs surrounding the city.

“If Newton has a decent turnout and a big margin for Markey, Markey is going to win big,” Payne said. “If it’s a low turnout and the margin is a little closer, that bodes well for Lynch.”

On the Republican side, Harvard Business School graduate and former Navy SEAL Gabriel E. Gomez has raised more money than former U.S. Attorney Michael J. Sullivan and State Rep. Daniel B. Winslow combined and leads in a recent poll.

Gomez campaign spokesperson Will Ritter that he was encouraged by an estimate from Secretary of State Galvin that turnout in the Republican primary would be higher than in 2009 by about 35,000 voters.

“[Higher turnout] means that there are people who are hearing about the election because they are interested in Gabriel Gomez, in our message, and in a candidate who is different,” Ritter told The Crimson on Monday night.

Joseph Selvaggi, a Republican who challenged Lynch in the 8th congressional district race last November, was not as optimistic about the projected turnout, which he said might not be high enough to be a game changer for Gomez.

“I don’t think the people will show up to vote in the way that the Gomez campaign thinks they will,” Selvaggi said, adding that a low turnout would probably favor Sullivan, who is seen as the most uniformly conservative of the Republicans.