Meteorologists also use a system called the Accumulated Cyclone Energy Index (ACEI) to calculate the energy produced by tropical-weather systems.
The measurement is based on a storm's wind speed, the duration of those winds, and the duration of the storm. The index can be applied to individual hurricanes, to all hurricanes during a particular month, and to an entire hurricane season.
Although there is more than a week left in July, this month already ranks as the third-most active on record, based on the ACEI, Masters said.
The three seasons with comparable July activity—1916, 1933, and 2005—ended up being three of the most active hurricane seasons on record. This season's July activity also surpassed that of 1916, which had ranked third until this year.
A storm is considered a major hurricane when it reaches Category 3. Such hurricanes have winds exceeding 110 miles (177 kilometers).
"That does not bode well for the coming season," Masters said.
"All three years—1916, 1933, and 2005—had five major hurricanes. I'd say the odds of more than one major hurricane hitting us are enhanced this year."
Phil Klotzbach, a meteorologist at Colorado State University in Fort Collins, said early-season activity usually isn't an indicator of how the rest of the season will develop—unless storms are already forming in the so-called deep tropics east of Puerto Rico.
And that's what is happening this year, he said.
"When you have storms like Hurricane Bertha—which formed in the deep tropics—that tells you that things are trying to go very early," Klotzbach said. "That tells you that prior to the first of August, things are ripe for formation."
Masters of Weather Underground also noted that Hurricane Bertha was a bizarre storm. It was named on July 3, became a Category 1 hurricane on July 7, and retained its status as a named system until July 20.
Bertha also surprised meteorologists by suddenly intensifying to a Category 3 only a few hours after it reached hurricane status.
In addition, Bertha also developed near the Atlantic Ocean's Cape Verde Islands, the birthplace of some of the most severe storms on record.
These so-called Cape Verde hurricanes don't usually develop until later in the season—making Bertha the earliest Cape Verde storm on record, Masters said.
Anybody's Guess
Not all meteorologists agree that July hurricane data can predict that the rest of the season will be busy.
"A high ACEI may not tell the story of what follows," said Lian Xie, a meteorologist at North Carolina State University in Raleigh. "You can't look at half the season and make a prediction."
Still, Xie acknowledges that this July has been an active month.
He also predicted an active 2008 hurricane season in April and sees no reason to alter his preseason forecast, which says that six to eight hurricanes will form before the season ends November 30.
"We're looking at an active season," Xie said. "How much more active is anybody's guess."
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