2010 Atlantic hurricane season forecast

I noticed that the media account did not mention the factor of the record level sea surface temperatures.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1493

Posted by: JeffMasters, 3:29 PM GMT on May 27, 2010

The National Oceanic and Atmospheric Administration (NOAA) issued its 2010 Atlantic hurricane season forecast today. NOAA forecasts a very active and possibly hyperactive season. They give an 85% chance of an above-normal season, a 10% chance of a near-normal season, and just a 5% chance of a below-normal season. NOAA predicts a 70% chance that there will be 14 - 23 named storms, 8 - 14 hurricanes, and 3 - 7 major hurricanes, with an Accumulated Cyclone Energy (ACE) in the 155% - 270% of normal range. If we take the midpoint of these numbers, NOAA is calling for 18.5 named storms, 11 hurricanes, 5 major hurricanes, and an ACE index 210% of normal. A season with an ACE index over 175% is considered "hyperactive." An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The forecasters note that in regards to the oil spill in the Gulf of Mexico,

"Historically, all above normal seasons have produced at least one named storm in the Gulf of Mexico, and 95% of those seasons have at least two named storms in the Gulf. Most of this activity (80%) occurs during August-October. However, 50% of above normal seasons have had at least one named storm in the region during June-July."

The forecasters cited the following main factors that will influence the coming season:

1) Expected above-average SSTs [SST = Sea Surface Temperatures] in the hurricane Main Development Region (MDR), from the Caribbean to the coast of Africa. SSTs in the MDR are currently at record levels, and the forecasters note that several climate models are predicting record or near-record SSTs during the peak portion of hurricane season (August - October.) "Two other instances of very warm SSTs have been observed in the MDR during February-April (1958 and 1969). In both years, the SST anomaly subsequently decreased by roughly 50% during the summer months. For 2010, although the record SST departures may well decrease somewhat, we still expect a continuation of above average SSTs throughout the Atlantic hurricane season. "

2) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO). "During 1995-2009, some key aspects of the tropical multi-decadal signal within the MDR have included warmer than average SSTs, reduced vertical wind shear and weaker easterly trade winds, below-average sea-level pressure, and a configuration of the African easterly jet that is more conducive to hurricane development from tropical waves moving off the African coast. Many of these atmospheric features typically become evident during late April and May, as the atmosphere across the tropical Atlantic and Africa begins to transition into its summertime monsoon state."

3) There will either be La Niña or neutral conditions in the Equatorial Eastern Pacific. El Niño is gone, and it's demise will likely act to decrease wind shear over the tropical Atlantic, allowing more hurricanes to form. "La Niña contributes to reduced vertical wind shear over the western tropical Atlantic which, when combined with conditions associated with the ongoing high activity era and warm Atlantic SSTs, increases the probability of an exceptionally active Atlantic hurricane season (Bell and Chelliah 2006). NOAA's high-resolution CFS model indicates the development of La Niña-like circulation and precipitation anomalies during July."

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