2007 Hurricane Forecast
|Named Storms||Hurricanes||Major Hurricanes|
|Long Term Average||10||6||2|
Presented here are the seasonal hurricane forecasts for the Atlantic basin produced by Dr. William Gray at Colorado State University and NOAA, along with our own discussion of the 2007 season. Click on the links below for more detail.
El Niño Impacts on the Hurricane Season
The year-to-year variability in tropical activity in the Atlantic is partially controlled by the El Niño-Southern Oscillation. It is well-known that a developing El Niño decreases the number of tropical systems that form in the Atlantic basin by creating an environment prone to unfavorable vertical shear. This decrease in tropical activity corresponds to less frequent hurricane landfalls along all portions of the U.S. coast. La Niña (colder than normal water in the eastern tropical Pacific) increases the formation of tropical storms and hurricanes, and a recent study co-authored by Dr. James O'Brien shows that this increase is manifested by more hurricane landfalls along the East Coast of the U.S. (Georgia to Maine). Neutral conditions and La Niña both coincide with an increased risk of landfalls along Florida and the Gulf Coast.
The left graph shows that Florida (both coasts) averages twice the number of landfalling hurricanes (the ones that count) during neutral conditions or a developing La Niña (cold) than during an El Niño (warm). The East Coast (Georgia to Maine) only sees this increase during a developing La Niña. This trend is detailed in probability of exceedence curves in the right-hand graph.
Trends in hurricane activity
As far as trends, Dr. Gray, Dr. Jim Elsner at Florida State University, and other experts have documented a 30-50 year cycle in tropical activity in the Atlantic Basin. A similar cycle exists in the Gulf of Mexico. They believe this cycle is tied to multi-decadal changes in sea surface temperatures and salinity in the North Atlantic Ocean, a manifestation of oscillations in the Atlantic Ocean thermohaline circulation (ATC). The fifty-year period from 1910-1960 can be classified as an active phase of this multi-decadal cycle, while 1960-1995 saw a fairly signficant decrease in hurricane activity. Since 1995, the level of hurricane activity has again been on the rise and it is theorized that it is tied to a recent shift in the ACT. Experts believe this new level of increased hurricane activity will last another 20 or more years.
There is no reason to believe that the recent increase in hurricane activity is tied to any alleged "global warming".