"Our first priority is ensuring the safety of delegates, alternates, guests, members of the media attending the Republican National Convention, and citizens of the Tampa Bay area," party chairman Reince Priebus said in an emailed announcement that followed private conversations involving presidential candidate Mitt Romney's campaign, security officials and others.
Priebus added that forecasters have predicted that convention-goers "may encounter severe transportation difficulties due to sustained wind and rain" on Monday, the day the convention had been scheduled to open.
The announcement said that while the convention would officially be gaveled into session on Monday as scheduled, the day's events would be cancelled until Tuesday.
That meant Romney's formal nomination would be postponed by a day, from Monday to Tuesday, but the balance of the four days of political pageantry and speechmaking would go on as scheduled.
The former Massachusetts governor campaigned in battleground Ohio during the day, pledging to help women entrepreneurs and innovators who are eager to create small businesses and the jobs that go with them. It was an economy-themed countdown to the Republican National Convention taking shape in a city already bristling with security - and bracing for a possible hurricane.
"Women in this country are more likely to start businesses than men. Women need our help," said the Republican presidential challenger, eager to relegate recent controversy over abortion to the sidelines and make the nation's slow economic recovery the dominant issue of his convention week.
The former Massachusetts governor campaigned with running mate Paul Ryan in battleground Ohio as delegates arrived in Florida by the planeload. Across town, technicians completed the conversion of a hockey arena along Tampa Bay into a red, white and blue-themed convention hall.
The announcement made the GOP convention the party's second in a row to be disrupted by weather. Four years ago, the delegates gathered in St. Paul, Minn., but Hurricane Gustav, slamming the Gulf Coast, led to a one-day postponement.
In that case, party officials rewrote their script to make President George W. Bush's speech into a video appearance, and to cancel plans for Vice President Dick Cheney to appear before the delegates. Both men were unpopular at the time.
Four years later, there was no immediate sign that Romney's forces would do anything other than squeeze two nights' of platform programming into one. Nor did it appear the postponement would cost them much, since the television networks had already announced they would not be carrying any of Monday's events live.
There was no hint in the announcement of a postponement of plans to evacuate the roughly 2,000 delegates eager to nominate Romney and Ryan as their ticket for the fall campaign.
"Federal, state and local officials assure us that they are prepared to respond, if needed, and the scheduling changes we are announcing today will help ensure the continued safety of all participants - our foremost concern," the announcement said.
"We are also committed to keeping the delegates and guests of the convention well informed about the situation, and we will continue providing updates in the hours and days ahead."
Despite the disruption, Priebus said, "we are optimistic that we will begin an exciting, robust convention that will nominate the Romney-Ryan ticket."
Plans had called for the convention to open Monday with quick ratification of a conservative platform expected, followed by Romney's nomination in a traditional roll call of the states timed for network evening news coverage.
Barring further postponements it ends Thursday with his acceptance speech, a prime-time appearance aides hope will propel him into a successful fall campaign and eventually, the White House.
The polls made the race a close one, narrow advantage to Obama, as two weeks of back-to-back conventions approached. Hundreds of millions of dollars have been spent on television ads, with hundreds of million more to come, almost all of it airing in a small group of battleground states expected to settle the election.
The list included Florida as well as North Carolina, where the Democratic National Convention will be held in one week's time.
After Romney's uneven run through the primary contests of winter and spring, the GOP convention was made to order for him from start to finish. Rick Santorum, Newt Gingrich and other foes from the long-ago primaries weren't even a nuisance as the four-day event approached.
But the same couldn't be said for Tropical Storm Isaac, lashing Haiti and Cuba as it churned menacingly through the Caribbean.
Florida Gov. Rick Scott declared a state of emergency earlier in the day as the storm approached the Florida Keys, more than 400 miles from Tampa. Forecasters said it was on a track to head west of the convention city, but predicted strong winds and rain at a minimum on Monday as the delegates were to board buses for their first trip to the hall.
"We are a hospitality state. We know how to take care of people and we want to ensure their safety," Scott said.
Apart from weather concerns, a heavy security presence was already in evidence. Miles of fencing were designed to create a secure zone around a tract of land that included the convention hall, the hotel where Romney will stay and a nearby convention center where journalists and others worked.
With demonstrations expected in the days ahead, National Guard troops armed with rifles patrolled nearby streets. They augmented police out in force, some on bicycles. Authorities reported no arrests.
Obama did his best to intrude on the Republican unity tableau.
In an interview with The Associated Press, he accused Romney of holding "extreme positions" on economic and social issues, while pledging a willingness on his own part to agree to "a whole range of compromise" with Republicans if he is re-elected.
He did not elaborate, but his pledge seemed designed to appeal to independents and other voters who say they are tired of seemingly perpetual campaign bickering and Washington gridlock.
But Romney said Obama's entire campaign rested on his ability to persuade people to ignore his record and listen instead to his rhetoric.
"It is not his words people have to listen to. It's his action and his record," he said in his appearance in Powell, Ohio. "And if they look at that, they'll take him out of the office and put people into the office who'll actually get America going again."
Romney's speech included an appeal to women made on economic grounds rather than on the basis of social issues like abortion, the sort of approach the Republican hopes will eat into Obama's polling advantage among female voters.
"I want to make sure that we help entrepreneurs and innovators. I want to speak to the women of America who have dreams, who begin businesses in their homes, who begin businesses out in the marketplace, who are working at various enterprises and companies," he said.
"Our campaign is about making it easier for entrepreneurs, women and men, to start businesses, to grow businesses," Romney said. He said most jobs are created by small businesses rather than larger firms or corporations.
Romney envisioned an economic resurgence fueled by abundant energy, expanded trade and a skilled workforce. If that happens, "America is going to surprise the world. We're going to stand out as a shining city on a hill in part because of our extraordinary economy," he said to the cheers of an estimated 5,000 supporters.
Romney's determination to turn the campaign's attention to the economy follows two weeks of controversy over Medicare, courtesy of Obama's campaign, as well as abortion, the result of a comment by Rep. Todd Akin, the party's candidate in a Senate race in Missouri.
Romney joined an unsuccessful effort by party leaders to force Akin to quit his race after he said women who are raped rarely become pregnant, a view unsupported by medical evidence.
He also fought back hard in recent days in person and television advertising against Obama's allegations that he and running mate Ryan would remake Medicare in a way that would undermine the health of future seniors.
Romney's objective appears to be to erode Obama's advantage among women voters and those who say Democrats are better equipped to handle Medicare, the giant health care program for seniors.
In the AP interview, Obama said it was Romney's promises that represented the real threat to the economy and the pocketbooks of millions.
"Mitt Romney is proposing a $5 trillion tax cut that disproportionately goes to the wealthiest Americans. And he will pay for that by gutting investments in things like education, infrastructure, basic science and research, voucherizing Medicare...."
Inside the Tampa Bay Times Forum, thousands of inflated red, white and blue balloons nestled in netting high above the arena floor, ready to be dropped in the traditional convention finale on Thursday night.
Technicians tested the microphones installed for each delegation, who will sit at the foot of a vast, made-for-television podium. Teleprompters where Romney will be able to see his acceptance speech scroll by were loaded - with phrases from Abraham Lincoln's immortal Gettysburg Address, lest the words the Republican presidential contender will use to launch his fall campaign for the White House leak in advance.
AP White House Correspondent Ben Feller and Associated Press writers Steve Peoples and Philip Elliott in Ohio, and Brian Bakst and Suzette Laboy in Florida contributed to this report.