July 10, 2012

El Nino and the 2012 Hurricane Season

Indications continue to point toward a building El Niño, a pattern that can greatly impact the second half of the hurricane season. During an El Niño, air is generally rising over the tropical Pacific and generally sinking over the tropical Atlantic. Rising air and low wind shear favors tropical storm and hurricane development, while sinking air and wind shear inhibits it.
However, according to Tropical Weather Expert Dan Kottlowski, "We continue in a lull of activity in the Atlantic now, but not necessarily from a developing El Niño." "During much of July, we usually see a rather routine separation of the main jet stream with the Atlantic, which often results in a quiet period in terms of tropical cyclones," Kottlowski said.
The main driver of tropical systems during the second half of the hurricane season is the flow of disturbances coming off of Africa, which pass near the Cape Verde Islands in the Atlantic. The disturbances pick up moisture and often intensify as they move westward over the warm tropical Atlantic waters.
If the pattern continues with the development of El Niño late in the summer and fall, a number of disturbances could tiptoe along across the Atlantic, only to ramp up near the East and Gulf coast of the United States, where waters are generally much warmer than average.
There is the possibility that the Atlantic season may be truncated somewhat earlier than average this year due to a moderate El Niño forecast by AccuWeather.com. However, there could be a pack of formidable storms over several weeks spanning August into September, before the full effects of El Niño come into play. Only if neutral conditions were to persist, or El Niño only reaches a weak status late in the game, then there would be less truncation and perhaps a more typical length of the Atlantic and Pacific hurricane season.
AccuWeather.com expects the number of tropical systems to be near-normal by the end of the season factoring in the early-season and likelihood of the mid-August to mid-September spike. With wind shear, dry air and dust issues now and later over the central Atlantic, there is still the danger of near-U.S. coast hurricane formation and impact mid- to late-season.
By Alex Sosnowski, Expert Senior Meteorologist – Accuweather.com

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