How El Niño and La Niña impact hurricane frequency, intensity and landfalls

Reinsurance broker Aon Benfield published their review of the 2011 global catastrophes and re/insured losses that resulted from them yesterday. We’ve covered this in detail in recent weeks (here, here and here) so won’t go into the loss experience of 2011 again. The report does contain one very interesting piece of information on the correlation of the El Niño/Southern Oscillation (ENSO) (and La Niña) with the frequency, intensity and number of landfalling hurricanes in the Atlantic ocean basin which we wanted to highlight.

25-Year Atlantic Hurricane Frequency By ENSO Phase

Aon Benfield comment on the different phases of the ENSO and how they impact the frequency and severity of the Atlantic hurricane season.

During El Niño Phases

• Overall hurricane frequency is below average
• Category 3 (sustained winds of at least 111 mph (179 kph)) hurricane frequency is below average
• Landfalling hurricane frequency is below average

During La Niña Phases

• Overall hurricane frequency is above average
• Category 3 (sustained winds of at least 111 mph (179 kph)) hurricane frequency is above average
• Landfalling hurricane frequency is above average

During Neutral Phases

•  Overall hurricane frequency is slightly above average
• Category 3 (sustained winds of at least 111 mph (179 kph)) hurricane frequency is near average
• Landfalling hurricane frequency is near average

The current La Niña is forecast to weaken as the year goes on meaning that the Atlantic hurricane season forecasts for 2012 are for an above average season but not as active as in the last few years. How that translates into landfalling storms is very hard to say. However, if you observe the weather patterns being experienced in the U.S. and Europe this winter, they are very different from the last two years and more akin to years in the mid-2000’s when hurricane landfalls seemed more common. It will be interesting to see how the changes in jet streams, prevailing climate patterns and the weakening La Niña affect the 2012 Atlantic Hurricane Season.