Mayor Martin J. Walsh, in a casual zipped-up black jacket, stood outside a Jamaica Plain train station early Friday morning for an hour of retail politicking — greeting residents, shaking hands, and posing for pictures.
“Remember to vote,’’ one of his volunteers reminded commuters as they hurried to catch a train at the Green Street stop on the Orange Line.
A few miles away, Walsh’s main challenger, City Councilor Tito Jackson, was stumping on a corner of Massachusetts Avenue, basking in the adoration of motorists who honked, waved, and gave him the thumbs up.
Boston’s preliminary election is Tuesday, but many people are only starting to pay attention to the challenge Walsh faces from Jackson and two other candidates. Experts who have closely followed Boston’s municipal elections predict a lot of voters will stay home. The top two finishers move on to the general election on Nov. 7.
Based on past Boston preliminary elections, Secretary of State William F. Galvin said he expects 60,000 of the city’s estimated 391,000 registered voters to cast their ballots, a 15 percent turnout rate.
Turnout in Boston has declined through the years, Galvin said, with many voters going to the polls only for major state and federal races.
“This is an election about. . . diehard supporters of the candidates,’’ Galvin said.
Paul Watanabe, a political science professor at the University of Massachusetts Boston, is predicting a higher turnout, around 30 percent.
Polls show Walsh cruising to victory. And since there are no other major state or national races in play this year, voters may wait for the general election, said Larry DiCara, a former city councilor and unofficial Boston political historian.
This is the way it often goes in Boston in off-year elections.
In the 2009 preliminary contest, when former mayor Thomas M. Menino fended off four challengers, turnout was a dismal 23 percent of the 353,683 registered voters, according to city election figures.
During the open contest in 2013, when Walsh first ran for mayor, 31 percent of 368,207 registered voters turned out in the preliminaries, city election officials said.
This year, Walsh and Jackson are sprinting through the weekend from one campaign event to the next to get their supporters to turn out on Tuesday.
“Regardless of who people vote for, I think it is important that people come out and express their democracy,’’ the mayor said. “I’d love for them to come out and vote for me obviously, but I’d like to see the [turnout] numbers up. I don’t like to see the single-digit turnouts around our city.”
Walsh has a commanding 31 percentage point lead over Jackson, according to a Suffolk University/Boston Globe poll. Trailing far behind them are East Boston residents Robert Cappucci, a former police officer and former elected School Committee member, and Joseph Wiley, a customer service representative at MassHeatlh.
While Walsh is all but guaranteed victory, he needs to win by a significant margin, as much as 40 percentage points, to show he has broad support, Watanabe said. Jackson needs to narrow the gap to prove he is a political force to be reckoned with.
“Publicly, Mayor Walsh is going to say that any victory is a victory,’’ said Watanabe. “I think he is going to look for an overwhelming victory.”
Watanabe said Jackson wants his key campaign issues — including inequality and affordable housing — to remain atop the city’s agenda even if he loses.
“If Tito gets anything above 25 percent he would be exceeding expectations,” Galvin said.
Jackson supporters say he is in the race to win. The candidate has spent the summer building up his name recognition across the city, with a much smaller campaign staff – and budget – than Walsh has.
Ronald Bell, a senior adviser to the campaign, said Jackson is making a hard push to get votes from communities of color and from people who feel disenfranchised.
“It’s going to be a grind — around the clock,’’ said Bell, who predicted “record turnout” in communities of color.
The mayor said his campaign has picked up steam, with more phone calls and knocking on doors.
“We are taking nothing for granted over these last few days before the preliminary election,’’ said the mayor’s campaign spokeswoman, Gabrielle Farrell.Meghan E. Irons can be reached at email@example.com. Follow her on Twitter @meghanirons.