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Distance travelled ~ 771'143'200 km

(Here Dr. Jeff Masters, Director of Meteorology, wunderground.com explores 2011's Atlantic Hurricane season. His previous post for 23 Degrees provided us with a detailed roundup of Maria, Nate and Katia's developments.)

The Atlantic is nearing its end, with Tropical Storm , near Mexico's Yucatan Peninsula, likely to be one of last storms of the season. Atlantic hurricane activity peaks near September 10, and drops dramatically during the last half of October. It's been a very strange year for hurricanes in the Atlantic. There have been a near-record number of named storms--seventeen--making 2011 the 7th busiest year for tropical storms since record keeping began in 1851. However, only six of those storms--35%--have intensified to hurricane strength. In a typical year, 55 - 60% of all tropical storms make it to hurricane strength. A rare combination of near-record warm ocean temperatures but unusually dry, stable air over the Atlantic is no doubt partially responsible for this very unusual occurrence. Another unusual feature of this hurricane season is that relatively few storms hit the U.S. During the 15-year active hurricane period from 1995 - 2009, 33% of all named storms in the Atlantic hit the U.S., and 30% of all Atlantic hurricanes hit the U.S. at hurricane strength. Based on 1995 - 2009 levels of activity, the U.S. should been hit by six named storms, four of those being hurricanes, and two being intense hurricanes. So far, 2011 has seen less than half that level of landfall activity. Two tropical storms and one hurricane have hit the U.S. this year: , which hit Texas with 50 mph winds, , which hit Louisiana with 60 mph winds, and , which hit North Carolina with 80 mph winds. This is the second consecutive year that the U.S. has benefited from favorable steering currents that have steered most of the storms out to sea. During 2010, only one tropical storm hit the U.S., despite a season with the 3rd highest number of named storms, nineteen. If 2011 finishes without a major Category 3 or stronger hurricane hitting the U.S.--which is likely--it will mark the first six-year period without a major hurricane strike on the U.S. since record keeping began in 1851. The last major hurricane to hit the U.S. was Category 3 Hurricane Wilma of October 2005.

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Figure 1. Tracks and intensities of the seventeen named Atlantic storms of 2011

The strongest hurricane of 2011 was , which peaked as a Category 4 hurricane with 140 mph winds and a central pressure of 940 mb on October 2 just northeast of Bermuda. Ophelia hit Southeast Newfoundland as a tropical storm with 70 mph winds on October 3, but caused little damage. The longest-lived storm was , which lasted 15 days from September 24 to October 8. The most damaging was , which caused at least $7 billion in damage from North Carolina to New England. Irene was also the deadliest storm of 2011, with 55 deaths in the Caribbean and U.S. being blamed on the storm.

Figure 2. Hurricane Irene as seen by NASA's Aqua satellite at 18:15 UTC on August 24, 2011. At the time, Irene was a Category 3 hurricane with 120 mph winds over the Turks and Caicos Islands.

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Image credit Western Carolina University

Figure 3. Hurricane Irene's storm surge and winds carved two new channels through Pea Island on North Carolina's Outer Banks. This cut, near the town of Rodanthe, is the smaller of the two cuts, and severed Highway 12 connecting the Outer Banks to the mainland.

What do you think of this year's season?

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