Danielle rapidly became a hurricane Monday and is expected to continue strengthening. It's still well out in the tropical Atlantic and likely will stay off the U.S. coast, but it probably will throw high surf onto South Carolina beaches by the weekend.

Behind Danielle, which on Monday night was about 1,205 miles east of the Lesser Antilles islands, another storm wave blew off Africa that's expected to become a tropical cyclone. There's another wave crossing the continent behind that one. It's the time of year for pummeling Cape Verde storms, the most dangerous to make landfall here.

"Danielle appears to be the first classic Cape Verde hurricane of this season," said Mark Malsick, South Carolina Climate Office severe weather liaison. Cape Verde storms are roiling West Africa monsoons that move into the Atlantic, turn into cyclones and curl toward the Southeastern coast.

"These are the seedlings," said Dennis Feltgen of the National Hurricane Center.

The Cape Verde season tends to run from August through September, but this year, Hurricane Alex, which began as a Cape Verde storm wave, smacked into Mexico in June. Forecasters continue to expect this to be what they call a "hyperactive" storm season.

"We don't see anything yet to make us change our minds," said meteorologist Tom Kine with AccuWeather.com, a private forecasting company.

The waves typically roll off the coast every three or four days -- an average of 60 to 70 per season, Feltgen said. On average, one in 10 become tropical cyclones.

Seven of the eight tropical cyclone storms that made landfall in South Carolina since 1954 formed during Cape Verde season. Three of them, including the catastrophic Hurricane Hugo in 1989, were "classic" Cape Verde storms blown off Africa. A fourth, devastating Hurricane Gracie in 1959, might well have been one.

Hurricane David in 1979 struck Florida, made its second U.S. landfall near Savannah then rolled through South Carolina. It also was a Cape Verde storm. Any number of the storms have raked the coast while passing just offshore, including Hurricane Floyd in 1999.

"With above-average heat content in the tropical Atlantic near Cape Verde, there is plenty of fuel for storms after Danielle to form," Malsick said. "Shear (winds) has been a continuing factor complicating previous potential storms this year and for Danielle. There are some indications that this persistent shear is starting to weaken."

S.C. landfalls

South Carolina tropical cyclone landfalls in recent history:

Oct. 15, 1954: Hurricane Hazel

July 11, 1959: Tropical Storm Cindy

Sept. 29, 1959: Hurricane Gracie

Aug. 21, 1976: Tropical Depression Dottie

Sept. 21, 1989: Hurricane Hugo

Oct. 11, 2002: Tropical Storm Kyle

Aug. 14, 2004: Hurricane Charley

Aug. 29, 2004: Hurricane Gaston*

*Gaston was categorized as a tropical storm at landfall, but later recharacterized as a hurricane.

Reach Bo Petersen at 937-5744 or bpetersen@postandcourier.com.