On average, the fourth storm of the six-month season does not occur until August 29. This year, the fourth, Dolly, formed on July 20 and was on the cusp of becoming a hurricane on Tuesday as it churned through the oil and gas-rich Gulf of Mexico.
"It absolutely does mean something, and we should be looking at it with trepidation," said Jeff Masters, co-founder of meteorological website The Weatherunderground.
The Atlantic hurricane season begins on June 1 but rarely gets into gear before August.
Statistically, most seasons that see as much early storm activity as this one turn out to have more tropical storms and hurricanes than the average, said Dennis Feltgen, a spokesman for the U.S. National Hurricane Center.
"We're definitely ahead of the curve here," said Feltgen, noting that the National Oceanic and Atmospheric Administration had predicted there was a 65 percent chance the 2008 season would be more active than average.
The 2005 season produced an unprecedented 28 storms, including Hurricane Katrina, which devastated New Orleans, killed 1,500 people on the U.S. Gulf Coast, and helped push oil prices to then record levels. By July 22, 2005, six tropical storms had formed, of which three became hurricanes.
An average Atlantic hurricane season sees 10 storms, of which six strengthen into hurricanes with winds of at least 74 mph (119 km per hour). In May, NOAA predicted there would be 12 to 16 named storms this year, of which six to nine would become hurricanes.