During the past 6-years since Hurricane Katrina, global tropical cyclone frequency and energy have decreased dramatically, and are currently at near-historical record lows. According to a new peer-reviewed research paper accepted to be published, only 69 tropical storms were observed globally during 2010, the fewest in almost 40-years of reliable records.

Furthermore, when each storm’s intensity and duration were taken into account, the total global tropical cyclone accumulated energy (ACE) was found to have fallen by half to the lowest level since 1977.

In his new paper “Recent historically low global tropical cyclone activity”, Dr. Ryan Maue, a meteorologist from Florida State University, examined the last 40-years of global hurricane records and found strikingly large variability in both tropical cyclone frequency and energy from year-to-year. Since 2007, global tropical cyclone activity has decreased dramatically and has continued at near-historical low levels. Indeed, only 64 tropical cyclones were observed globally in the 12-months from June 2010 – May 2011, nearly 23-storms below average obliterating the previous record low set in 1977.

On average, the North Atlantic including the Gulf of Mexico and Caribbean Sea accounts for about 1/8 of total global tropical cyclone energy and frequency. However in 2010, the Atlantic saw 19 tropical storms, of which 12 became hurricanes as expected (and forecasted) due to the intense La Nina event and continued positive Atlantic Multidecadal Oscillation (AMO). The Atlantic Ocean’s accumulated cyclone energy (ACE) corresponded to about 1/3 of the global calendar year output while the Western North Pacific typhoon season experienced a record few number. Seasonal forecasters of Atlantic hurricanes expect a similar but somewhat tempered outcome for the 2011 season, which has yet to get underway.

While the North Atlantic continued a 16-year period of above-normal activity in 2010, the North Pacific including the warm tropical waters from China to Mexico experienced the quietest tropical cyclone season in at least 40-years of historical records. Similarly, the most recent Southern Hemisphere cyclone season, except for the disastrous impacts of Yasi, was also notably below average. All told through June 27, 2011, overall global accumulated cyclone energy and frequency has settled into a period of record inactivity.

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Abstract of paper:

Tropical cyclone accumulated cyclone energy (ACE) has exhibited strikingly large global interannual variability during the past 40‐years. In the pentad since 2006, Northern Hemisphere and global tropical cyclone ACE has decreased dramatically to the lowest levels since the late 1970s. Additionally, the global frequency of tropical cyclones has reached a historical low. Here evidence is presented demonstrating that considerable variability in tropical cyclone ACE is associated with the evolution of the character of observed large‐scale climate mechanisms including the El Niño Southern Oscillation and Pacific Decadal Oscillation. In contrast to record quiet North Pacific tropical cyclone activity in 2010, the North Atlantic basin remained very active by contributing almost one‐third of the overall calendar year global ACE.

Citation: Maue, R. N. (2011), Recent historically low global tropical cyclone activity, Geophys. Res. Lett., 38, LXXXXX, doi:10.1029/2011GL047711.

Figure 1: (Updated: June 1) Last 4-decades of Global and Northern Hemisphere Accumulated Cyclone Energy: 24 month running sums through June 1, 2011. Note that the year indicated represents the value of ACE through the previous 24-months for the Northern Hemisphere (bottom line/gray boxes) and the entire global (top line/blue boxes). The area in between represents the Southern Hemisphere total ACE.

Figure 2: (Updated: June 1) Last 4-decades of Global Tropical Storm and Hurricane frequency — 12-month running sums. The top time series is the number of TCs that reach at least tropical storm strength (maximum lifetime wind speed exceeds 34-knots). The bottom time series is the number of hurricane strength (64-knots+) TCs. The added red lines are linear trends, which serve the useful purpose of delineating the respective time-series mean, since they are flat and parallel. Updated through June 1, 2011.

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