Updated: 4:11 p.m.

Correction Appended

All signs are suggesting that Rep. Connie Mack IV will formally enter Florida’s Senate contest Friday morning, joining what will likely be a crowded and powerful Republican field fighting for the chance to challenge Sen. Bill Nelson (D) in 2012.

Mack will make a “major announcement regarding the U.S. Senate race” Friday morning in Fort Myers, according to campaign spokesman David James. The 10 a.m. event will be held on the steps of the historic Lee County Courthouse.

While he would not reveal what the announcement will be, it is widely believed that the four-term Congressman will announce his Senate candidacy, attempting to follow in the footsteps of his father and namesake. James did not rebut that when asked by Roll Call on Thursday afternoon.

The move by Mack, son of former Sen. Connie Mack III (R-Fla.), is not a surprise. For months, the 43-year-old Congressman has been positioning himself for a run at Nelson, the last Florida Democrat to hold statewide office and a top GOP target in 2012.

Mack hired major GOP fundraiser Anne Ekurn last month, a move that followed the addition of four staffers in early January. Ekern has previously raised money for the National Republican Senatorial Committee, as well as for several Senators and candidates. The St. Petersburg Times reported Ekern has raised money for Florida Republicans Bill McCollum, a former Congressman and Senate and gubernatorial candidate, and former Sen. Mel Martinez.

It is likely to be an expensive and hard-fought Republican primary.

There are already two Republicans in the race — Col. Mike McCalister and state Senate President Mike Haridopolos — and two more legitimate candidates — former Sen. George LeMieux and former state House Majority Leader Adam Hasner — are expected to follow in the relatively near future.

Correction: March 24, 2011

The article incorrectly stated that Mack would make an announcement in Tampa, Fla. It will be in Fort Myers.