Jeff Masters - Arthur's formation is not a harbinger of an active hurricane season

[malaise]

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2717
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The first hurricane of the season typically occurs on August 10, so Arthur is quite a bit ahead of schedule. Arthur was able to form so early because it was over the very warm waters of the Gulf Stream Current, and these waters happened to be over 1°F warmer than usual for this time of year. Formation of a June or July hurricane like Arthur off the U.S. coast is typically not a harbinger of an active hurricane season, since these storms do not form from African tropical waves. Arthur spun up from a cluster of thunderstorms and their associated low pressure system that moved off the Southeast U.S. coast, and hurricanes that get their start this way are typically too far north and too close to land to be able to intensify into major hurricanes. The bigger threat are hurricanes that get their start from tropical waves traversing Main Development Region (MDR) for hurricanes (from the coast of Africa to Central America between 10° - 20°N, including the Caribbean Sea.) Tropical waves that traverse the MDR are responsible for 85% of all major (Category 3 and stronger) hurricanes. When June and July hurricanes and tropical storms form in the MDR, it usually does portend an active hurricane season, since it shows that atmospheric and oceanic conditions are primed to assist development of tropical waves coming off the coast of Africa during the peak mid-August through mid-October part of hurricane season.

A better way to evaluate whether or not this will be an active hurricane season is to look at sea surface temperatures (SSTs) in the MDR, and the status of El Niño. MDR SSTs are currently very close to average, and are thus unlikely to contribute to an above-average hurricane season. The very warm equatorial waters currently off the coast of South America suggest that an El Niño event is in the process of developing. When an El Niño event occurs during hurricane season, it tends to create an atmospheric circulation that brings unusually strong upper-level winds to the tropical Atlantic. These strong winds create a shearing action (wind shear) on any tropical storms or hurricanes that may be attempting to form, disrupting their circulation. Thus, the pre-season predictions of a below-average or near-average hurricane season still look good.
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On the other hand just imagine what they are about to face with Typhoon Neoguri
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