True to Forecast, Atlantic Hurricane Season Kicks into High Gear

By Andrew Freedman

Graphic showing the number of storms in the 2010 hurricane season to date, compared with an average season to date and the NOAA outlook for the entire 2010 hurricane season.
Click on the image for a larger version. Credit: Russell Freedman.

The 2010 Atlantic hurricane season just passed its climatological peak, and as projected, it’s been an above-average year for Atlantic storms. So far, five hurricanes have formed in the Atlantic, three four of which — Danielle, Earl, and Igor, and Julia — have reached major hurricane status with sustained winds greater than 111 mph. In fact, Hurricane Igor, which at its strongest point had sustained winds of up to 150 mph, was the strongest hurricane in the Atlantic basin since Hurricane Felix in 2007.

Despite the above average hurricane activity this season, coastal residents in the U.S. have largely breathed a sigh of relief, since no hurricane has made landfall yet (although there was the close brush with Hurricane Earl at the beginning of September). This is largely thanks to prevailing weather patterns, which have featured strong troughs of low pressure moving off the East Coast. These dips in the jet stream have formed a kind of defensive line against incoming storms, pushing hurricanes away from the mainland.

Therefore, the especially dangerous Cape Verde-type hurricanes have first headed westward off Africa, and then turned northwest, followed by an accelerating turn to the north/northeast well before they reach the U.S. coastline. This has meant that most hurricanes this season have been what some meteorologists refer to as “fish” storms, since they mainly affect the fish in the sea.

In their outlook for the 2010 hurricane season, which was updated in August, the National Oceanic and Atmospheric Administration (NOAA) stated there was a 70 percent likelihood that there would be 14 to 20 named storms (tropical storms and hurricanes), eight to 12 hurricanes, and four to six major hurricanes. So far that forecast is verifying, at least at the lower end of the numbers. Forecasters say that the presence of El Nino or La Nina, along with Atlantic sea surface temperatures, can account for about half of the variability in the Atlantic hurricane season, with day-to-day weather fluctuations responsible for the rest. This season there is a combination uniquely suited for a very active hurricane season, with a La Nina event in the Pacific Ocean and record warm Atlantic sea surface temperatures.

However, capricious day-to-day weather patterns have interfered with storm development in several instances, demonstrating that larger-scale climate factors do not necessarily guarantee a particular outcome. One meteorological phenomenon that can affect storm behavior is known in weather geek-speak as “TUTT,” which stands for “Tropical Upper Tropospheric Trough.” In certain cases, such troughs can make the environment more hostile for storms to intensify or maintain their strength.

Several incipient storms this year, such as Tropical Storm Gaston, have been disrupted by areas of dry air, which can choke off the thunderstorms that form the core of a tropical cyclone, as well as wind shear that can disrupt a storm’s circulation. Both of those forces weakened Hurricane Earl as it made its way off the eastern seaboard, for example.

Hurricane season runs through November 30, and historically both September and early October can be very active months.

You can track active storms, and obtain multimedia background information on factors influencing the 2010 hurricane season at Climate Central's hurricane features page