Just days after Seattle Mayor Ed Murray announced he's not running for re-election, the race to replace him is heating up.

KING 5 has confirmed that Seattle Councilmember Lorena Gonzalez, a former advisor and legal counsel to Mayor Murray, is seriously considering a run.

“We will have more to announce soon,” said Christian Sinderman, her campaign consultant who also had worked on Mayor Murray’s re-election campaign.

Meanwhile, former U.S. Attorney Jenny Durkan will officially launch her campaign on Friday morning, bringing the total number of candidates in the race to 13.

Related: Who's in and who's out of the Seattle mayoral race, plus the endorsements now up for grabs

Durkan gave an early preview of her announcement in a blog post on Medium.

“I am guided by a deep believe in seeking justice and fighting for the underdog,” Durkan writes in part.

She describes herself as a progressive leader and former dues-paying Teamster, a nod to labor unions who had previously endorsed Mayor Murray.

“That union job helped me pay for law school,” she said in the blog post.

Durkan, whose background includes civil litigation and criminal defense, also served as a longtime legal advisor to former Washington Governor Chris Gregoire.

Durkan, representing the State Democratic Party, fought to defend Gregoire’s narrow 2004 win over Dino Rossi when the nation’s closet governor’s race was challenged in court.

Former Governor Gregoire says she proved her toughness back then, after insisting on delivering the closing argument the day after her father passed away.

“She arrived at the courtroom, timely the next morning and said my dad would want me to do this. I'm going to do it. That's who were talking about,” Gregoire recalled.

Gregoire, a longtime friend of Durkan, began making calls on her behalf this week to ask for support for her upcoming mayoral run.

“I think we need steady, progressive leadership; someone who can bring us together, set an agenda, get things done, make decisions. That's who she is,” said Gregoire.

“She’ll swing into action; she’ll get things done. She’ll work well with people in the community. She’ll work well with County Executive, she’ll work well with leadership in Olympia. That’s really what this community needs now.

Gregoire said Durkan plans to focus on issues including education, homelessness, transportation and affordable housing.

The former U.S. attorney, appointed in 2009 under President Obama, also made a name for herself in the areas of police accountability and reforms. She helped to negotiate the current federal consent decree that forced change within the Seattle Police Department.

“He choose her because she was incredibly capable and thoughtful and knew how to lead and, in a crisis, could make good decisions,” said former County Executive Ron Sims, a fellow Obama appointee. “You need all of those qualities to be a mayor of a city.”

Sims, who had endorsed Mayor Murray prior to his announcement Tuesday, says he will now back Durkan.

“I’m looking for a person who has a short training period - really short. You have to come in and grab the reigns really quickly,” said Sims.

“I think Jenny Durkan becomes the front runner tomorrow. She brings so much, both family name, her own talents, her own skills, incredible network,” he continued.

Durkan’s father, Martin Durkan, was a powerful state lawmaker and former gubernatorial candidate. Her campaign announcement on Friday will take place at a location on Beacon Hill where her father recovered from injuries after World War II, according to a campaign spokesperson.