Hurricane factoids

2010 has seen quite an active hurricane season in the Atlantic Ocean. Let’s take a look at a few storm facts:

• In 2010, there were 14 named storms, of which 7 were hurricanes and 5 were major hurricanes (that is, category-3, 4 and 5 ones). Hurricane activity this year was about 1.5 times the median hurricane activity level.


• A hurricane is an intense tropical storm. Tropical storms form over warm tropical oceans when local sea surface temperatures are above 26.5°C (80°F) through a depth of at least 50 meters (160 ft). Under these conditions, evaporation from the ocean surface creates very high humidity in the atmosphere, which in turn generates thunderstorms.


• Hurricane forecasters were pretty much bang on target this year in terms of the number of hurricanes they predicted.


• A surefire way to kill a hurricane? Add something called “vertical wind shear” — essentially a change in wind speed and direction with height. It stops the storm from forming in its tracks by ripping it apart.


• Another way to kill a hurricane? Whip up a wind across the deserts of northern Africa. Dust gets swept up into the air and helps damp down developing storms. (In fact, it’s the effect of the dust combined with vertical wind shear and super-dry air that’s the killer.)


• Monsoons in West Africa strongly influence hurricane activity on seasonal and decade-to-decade timescales.


• In the Atlantic, more than half of tropical storms and weak hurricanes and 85 percent of major hurricanes come from Africa.


• Many hurricanes are born in the “main development region” (MDR), which includes the Caribbean Sea and tropical Atlantic Ocean between latitudes of about 10°N and 20°N. When sea surface temperatures in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.)

But is climate change responsible for brewing more, and stronger, hurricanes? There’s a school of thought that says that climate change should fuel more hurricanes and more intense ones, because as the planet warms, ocean waters warm and sea surface temperature rises.

In a paper published earlier this year in Science, Thomas R. Knutson, of the Geophysical Fluid Dynamics Laboratory at the National Oceanic and Atmospheric Administration (NOAA) and co-authors suggest that we should expect an increase in the frequency of the strongest hurricanes in the Atlantic, roughly by a factor of two by the end of the century, despite a decrease in the overall number of hurricanes. “But we should not expect this trend to be clearly detectable until we near the end of the century, given a scenario in which CO2 [carbon dioxide] doubles by 2100.” The relationship will become more apparent as we improve our understanding and data and as the climate continues to warm.

(Knutson offers a review of the published research findings on this topic to date here.)

In the meantime, the storm-chasing will continue.