Cold Arctic air over the Atlantic Ocean.
Its persistence is why the number of hurricane-force events rose in the 2013-14 cold season versus three previous ones, according to the Ocean Prediction Center. The events were also much stronger this season.
Events can include extratropical and post-tropical storms and can result from a strong pressure gradient without a low pressure system, according to a center tweet.
Moreover, most of the systems developed hurricane-force winds (at least 74 mph) in the eastern Atlantic, with many affecting Ireland and the United Kingdom, according to the center.
I visited Ireland in April and was very fortunate to avoid one of those storms and enjoy great weather.
As I noted in a blog yesterday, 47 hurricane-force events happened in the North Atlantic from June 1, 2013, through May 2014, according to the center. Forty took place in 2012-13 and 2011-12 and 33 formed in 2010-11.
Of the 47 events, 37 rapidly strengthened (bombogenesis) and 15 had central pressures of 950 millibars or less, according to the center. Fifteen is roughly double the totals in the three previous seasons.
In comparison, only 27 hurricane-force events were recorded in the Pacific this cold season, and 18 of them rapidly intensified, according to the center. Three had central pressures of 950 millibars or less.
Those numbers are lower than in the previous three seasons, largely because of the persistent cold Arctic air over the Atlantic, according to the center.