Despite forecasts of an above-average Atlantic hurricane season, none of the seven tropical storms experienced so far this year have reached hurricane strength, making 2013 the first year in more than a decade to not have produced a landfall by August.

According to Claire Souch, vice president of model solutions at RMS, hurricanes have been unable to form so far in 2013 due to higher-than-normal wind shear in the atmosphere, cooler sea temperatures in the eastern Atlantic, and sand and dust particles from the Saharan air that have been pushed into the atmosphere, disrupting hurricanes that would normally be formed by tropical waves coming from western North Africa.

The Atlantic hurricane season has been relatively quiet, with eight tropical storms and no hurricanes. Last year at this time there were 13 named storms and seven hurricanes.

Tropical Storm Humberto formed near the Cape Verde Islands on Sept. 9 and was expected to strengthen into the first hurricane of the Atlantic storm season, but it is not expected to threaten the U.S.

The well-known hurricane forecasting team of Philip Klotzbach and William Gray at Colorado State University called for 18 named storms in the Atlantic this season, with eight hurricanes and three major hurricanes. Klotzbach told Reuters the duo would "back down from the prediction considerably" if they put out a mid-season update.

But forecasters still warn of complacency.

Last year, Superstorm Sandy, which caused more than $22 billion in insured losses as the second-costliest hurricane in U.S. history, occurred in late October.

RMS says September is the busiest month for hurricanes, averaging 2.1 each year, and predicts that if current windshear settles, a significant hurricane event could still occur due to warmer sea surface temperatures.

"Models are currently forecasting significant development potential for enhanced tropical storm development over the coming weeks, with an expected decrease in the inhibiting factors, making conditions favorable for late-season development," says Souch.

Humberto would be the latest date a hurricane has formed in the Atlantic during the hurricane season since Hurricane Gustav reached 74 mph on Sept. 11, 2002.

The prior year Erin was the first storm to reach hurricane status on Sept. 9, which didn't stop the 2001 season from exceeding all forecasts with 15 named storms, nine hurricanes and four major hurricanes. Nevertheless, the U.S. wasn't affected by any hurricanes in 2001.

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