MIAMI – Hurricane Frances, the third major hurricane of the month, exploded into a Category 4 monster Saturday over the Atlantic Ocean, and forecasters advised South Floridians to begin making calm, prudent preparations – just in case.

Though it remains far out to sea and many things can happen, Frances could grow even more viciously potent. At the moment, it is adhering to a course that could threaten the Bahamas and Florida by the end of this week.

“We have a major hurricane heading in our general direction, and it would make pretty good sense to dust off your hurricane plan,” said Max Mayfield, director of the National Hurricane Center in West Miami-Dade County.

“Why wait until midweek when things are busy?” he said. “Do it on Sunday. Check your water and batteries and so on. That’s what I’m going to do.”

Believing that Frances is likely to strike somewhere along the U.S. East Coast, Mayfield sought activation of a response team from the Federal Emergency Management Agency. In addition, he requested meteorological reinforcements to augment his forecasters later this week.

“We’re going to need it,” he said. “We’ve been busy.”

After a slow start to the season, the tropics suddenly have become a hurricane factory.

In addition to Frances, a strong tropical storm lurked off South Carolina’s coast Saturday, and a tropical depression appeared to be forming near Bermuda. On Florida’s southwest coast, residents were still dealing with the aftermath of Hurricane Charley. And the peak of the tropical weather season hasn’t even arrived yet.

“This is the last thing any of us need right now,” Mayfield said.

At the same time, he urged South Floridians not to make the same mistake made by some residents of the Gulf Coast, who said they were caught by surprise earlier this month when Charley’s core reached land at Port Charlotte instead of Tampa Bay, about 50 miles north.

“Don’t concentrate on the center line of the forecast,” he said. “Remember there is a margin of error, and everyone in a hurricane warning area has to take action.”

Still about 1,800 miles from the mainland, Frances is expected to keep moving northwest and west for several days, forced toward the Bahamas and Florida by a wide high-pressure system that sits north of it, blocking a turn in that direction.

Forecasters say a breach in that roadblock might allow it to curve away from us later this week, but that remains to be seen.

As Frances makes up its mind, it is moving slowly, which gives anyone in its way time to prepare. At its current speed, it is not expected to threaten Florida or anywhere else on the East Coast until Friday.

But that slow forward progress also gives the hurricane time to intensify, and the warm Atlantic gives it the fuel.

The conditions are similar to those that drove Hurricane Andrew into south Miami-Dade almost exactly 12 years ago.

“We don’t want to overdo that,” Mayfield said, “but to some extee season began June 1, but the first tropical depression didn’t form until July 31. Since then, the tropics have come alive. The tally: seven named storms, which became four hurricanes, three of them intense.

“It is remarkable to have three major hurricanes in August,” said hurricane forecaster Lixion Avila. “That certainly isn’t something that happens every year.”

The news doesn’t get better: Though the end of August generally is an active period, the statistical peak of the season doesn’t arrive until Sept. 10.