Updated 7:10 p.m. - TAMPA, Fla. -- Republicans announced Saturday that they had effectively canceled the first day of their convention for safety concerns associated with an impending hurricane.

Republican National Committee Chairman Reince Priebus said in a statement that "the Republican National Convention will convene on Monday August 27th and immediately recess until Tuesday afternoon, August 28th."

That move essentially postpones the activities of the first of four scheduled days of the convention. But Priebus said in a conference call with reporters that the details of the revised schedule were not yet settled, and could be announced as soon as Sunday.

"The Republican National Convention is going to take place. We know that we will officially nominate Mitt Romney and Paul Ryan," he said.

Romney will now be formally nominated as the Republican Party's presidential candidate on Tuesday instead of Monday, said Russ Schriefer, a senior strategist for the Romney campaign.

"Right now, we expect that the roll call will just take place on Tuesday," he said.

Convention organizers had pushed ahead with the gathering as planned for much of the week, even as it seemed, for some time, that Isaac was on a direct trajectory toward Tampa.

Simultaneously, the Obama campaign said that a bracketing trip by Vice President Joe Biden to Tampa -- which they had postponed -- would officially be canceled.

The impending hurricane aside, Republicans already did some last-minute reshuffling for their convention order, moving Ann Romney's speech to Tuesday from Monday because major television networks hadn't planned to broadcast the first night of the convention.

Following that change, the main speakers on Monday had been set to be South Carolina Gov. Nikki Haley, former Arkansas Gov. Mike Huckabee and former Florida Gov. Jeb Bush.

Schriefer also dismissed worries that the constrained schedule would hamper the GOP's ability to drive its message in this key swing state.

"Even though the time of the convention will be abbreviated...we will absolutely be able to get our message out," he said.

Bill Harris, the convention's president and CEO, said the convention organizers "will continue providing updates in the hours and days ahead."