2007 hurricane forecasts skewed by winds and dry, dusty air from Sahara

Science Daily: A new analysis of environmental conditions over the Atlantic Ocean shows that hot, dry air associated with dust outbreaks from the Sahara desert was a likely contributor to the quieter-than-expected 2007 hurricane season.

Factors known to influence the number and intensity of hurricanes in a season, including El Niño, sea surface temperatures, wind, and sea level pressure, led to NOAA forecasts [identify what agency made these forecasts; otherwise it might be assumed they are from NASA] for an above-average 2007 hurricane season. However, the season, which runs from June through November, turned up six hurricanes – a near normal number, but less than the 10 expected and far fewer than the record-breaking 15 hurricanes in 2005.

The difference between the 2007 and 2005 seasons could be due in part to the westward reach of Saharan dry air and dust over the North Atlantic, according to researchers, including Bill Lau of NASA's Goddard Spaceflight Center in Greenbelt, Md., and co-author of a study on this finding published Aug. 14 in the American Geophysical Union's Geophysical Research Letters. The study also confirms the possible role of Saharan dust in shattering predictions for the 2006 hurricane season, and has implications for more accurate predictions for future hurricane seasons.

Lau and colleagues previously reported that the presence of dust could have contributed to a weaker 2006 hurricane season than forecasters expected. Dust over the North Atlantic blocked some sunlight from reaching the ocean, accounting for 30 to 40 percent of the drop in sea surface temperatures measured between June 2005 and June 2006. The cooler sea surface increases atmospheric stability and also reduces the transfer of heat from ocean to atmosphere – a major source of fuel that drives hurricanes….

A dust plume from Northern Africa moves over the Atlantic on July 20, 2007. The westward extent of such dust could have contributed to the relatively quiet 2007 hurricane season. Shot by the busy satellites of NASA