Originally back in May, the National Oceanic and Atmospheric Administration (NOAA) called for an average 2012 hurricane season in the Atlantic predicting nine to 15 named storms this year. Then, near the season’s peak some 3 months later in August, it upped its prediction to 12 to 17 named storms, with five to eight of those becoming hurricanes, calling for in fact a busier than average season.
Now it’s October and it’s been one of the busiest seasons on record. With 19 named storms so far this year, 10 of which became hurricanes, including Hurricane Sandy, this season ties as the third most active on record. That puts the 2012 Atlantic hurricane season in rare company. Only seven seasons since 1851 (since the start of hurricane recording) have seen 19 or more named storms. Three of these have come within the last decade including the 2010 and 2011 seasons which both had 19 storms each and of course the unforgettable 2005 season which had a whopping 28 storms, the most on record.
It’s relatively unusual to have more storms than forecast, said Gerry Bell, the lead hurricane season forecaster at NOAA’s Climate Prediction Center.
So why has this hurricane season been busier than expected?
El Nino or the lack thereof is largely to blame for the busier than normal season. Weather forecasters predicted that this climate pattern, characterized by warm surface temperatures in the Pacific Ocean, would have developed by now and stymied hurricane formation by its influence on the atmosphere. But it hasn’t.
Bell said the hurricane forecast represents how many storms there are likely to be, within a 70 percent probability. In recent years their forecasts have been 95 percent accurate, he said.
Wind shear is the main way El Niño thwarts cyclone formation
This year, cyclone activity has continued longer than expected in the Atlantic, unperturbed by El Niño, which spawns high-level winds that stream eastward (also known as wind shear) capable of disrupting the swirling motion that gives a developing storm its power, according to Bell.
“There was a strong indication that El Niño would form in time to suppress the peak of the hurricane season and El Niño just hasn’t formed yet,” he said.
Other climate factors have also played a part in this year’s busy season, as well as some of the other recent busy seasons
The main reason for the recent abundance of cyclones is particularly since 1995 is because the Atlantic Ocean basin has been in the warm phase of a cyclical climate pattern called the Atlantic Multidecadal Oscillation, with hotter-than-average surface temperatures throughout the tropics and subtropics, according to Bell.
This pattern lasts for about 25-40 years, and comes with more hurricanes than its “cool” phase, he said. Warm water helps hurricanes form and fuels their strength.
In addition, in the past few years there has also been a strong West African monsoon, which has contributed in the increase number of cyclones in the eastern Atlantic, Bell said.
One thing that likely isn’t to blame for the increase in hurricanes in recent years is global warming, Bell said. Many climate models suggest that increased temperatures could actually lead to fewer, but stronger, hurricanes worldwide, he said.
Despite the fact that we have seen one of the busiest hurricane seasons on record, Phil Klotzbach, a hurricane expert at Colorado State University made note of the fact that the hurricanes this year have been shorter lived than normal. According to Dr. Klotzbach, while this year has produced 10 hurricanes, they’ve lasted only a total of 23 days. An average hurricane season has six hurricanes, but also about 25 hurricane days. In addition, the cyclones this year haven’t been as strong as usual, with only one major hurricane.
Furthermore, Dr. Klotzbach argues that the better technology over the past few decades have led to more detection of tropical cyclones that last less than 36 hours via satellite. This year there have been three tropical storms that have lasted less than 36 hours including tropical storms Helene, Joyce and Patty. Back in the pre-satellite era, these storms might have been missed, meaning more seasons may have been as busy as this one has been.
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