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Posted at 01:11 PM ET, 11/28/2012

Third most active hurricane season on record (tie) ends Friday


2012 Atlantic tropical cyclones

The 2012 Atlantic hurricane season is coming to an end. Although the official end is on Friday, it looks very likely that the final advisory from the National Hurricane Center was actually for Sandy, just prior to its New Jersey landfall back on the night of October 29th.

In an average season (using 1981-2010 as a baseline), there are 12.1 named storms, 6.4 hurricanes, and 2.7 major hurricanes. This season ended up with 19 named storms, 10 of which became hurricanes, but just 1 of those became a major hurricane (defined as category 3 or higher on the Saffir-Simpson hurricane wind scale). The 19 named storms ties for the third greatest number of such storms in a season on record. Historically, only about 3 percent of seasons experience 19 or more named storms. As rare as this feat is, it was amazingly the third consecutive season to have 19 named storms!

Despite this year’s large number of named storms, major hurricane activity was minimal. Of all the seasons with at least 19 named storms, the previous lowest number of “major hurricane days” was 3.75. This year, the total was a meager 0.25 days (six hours).


Hurricane Michael was the strongest storm of the season, and the only major hurricane. This visible satellite image shows Michael at its peak intensity on September 6. (NASA)
This season was also unusual in that very little of the hurricane activity actually took place in the tropics. With the exception of Ernesto and Sandy, every other hurricane formed north of 22 degrees north latitude. And Michael, the only major hurricane, was born from a mid-latitude low pressure system, not from anything tropical.

Another metric for evaluating seasonal activity is known as Accumulated Cyclone Energy, or ACE. ACE is basically a wind energy index used to succinctly characterize a season by the intensity and duration of all of the storms. The 2012 season finished up at 126.2, or about 137 percent of an average season. The median value over the period 1951-2010 is 92.4, and any season that exceeds 103 is considered to be “above normal”; however, there must also be at least two major hurricanes to meet the “above normal” criteria. As of now, Michael is 2012’s only major hurricane, but it’s quite possible that Sandy will be upgraded to a major hurricane when it was near Cuba. Nadine, the fifth-longest-lasting storm on record, contributed to 20% of the total ACE, while Sandy contributed to 11% of the total.

Many storms this season came in first or second place for the earliest formation dates. Beryl was the second earliest second named storm in a season (May 26), Debby was the earliest fourth named storm (June 23), Florence was the second earliest sixth named storm (August 4), Joyce was the second earliest tenth named storm (August 23), Kirk was the second earliest eleventh named storm (August 28), Leslie was the second earliest twelfth named storm (August 30), Michael was the second earliest thirteenth named storm (September 4), and Tony was the second earliest nineteenth named storm (October 24). Beryl was the strongest pre-season storm to make landfall on the U.S. in recorded history. We also saw four named storms by the end of June for the first time in recorded history.

Another impressive aspect of this season is that the United States avoided a major hurricane landfall for the seventh consecutive year. Hurricane Wilma was the last major hurricane to strike the U.S. coast back on October 24, 2005. As of today, that equates to 2,592 days. With a fair assumption that the next greatest chance of a major hurricane striking the U.S. coast is around the long-term mean of September 11, that span would reach an incredible 2,879 days. The previous longest span was 2,232 days (between the 1900 Galveston hurricane and the 1906 Florida Keys hurricane).


Historic record of the number of days between major hurricane landfalls on the U.S. coast. (adapted from rogerpielkejr.blogspot.com)

Never in known history has the U.S. been so fortunate in avoiding the devastation brought on by category 3-5 hurricane landfalls. One doesn’t need to be a fortune teller to predict that such a streak will end eventually, and hopefully this long vacation that we’ve enjoyed hasn’t made us complacent. Recent landfalling storms like Ike, Irene, Isaac, and Sandy were category 1-2 hurricanes (technically, Sandy just became an extra-tropical cyclone with hurricane-force winds at the time of landfall), which can produce a lot of flooding, but don’t come with the intense destructive winds.

In terms of a human and economic impact, the most memorable and significant landfalls include Ernesto (85 mph, eastern Yucatan peninsula), Isaac (80 mph, southeastern Louisiana), Sandy (80mph, Jamaica), Sandy (110 mph, eastern Cuba), Sandy (105 mph, Bahamas), and Sandy (90 mph, southern New Jersey). However, other weaker storms also contributed to the seasonal death toll and damage: Beryl, Debby, Helene, Leslie, and Rafael. These eight storms resulted in a combined death toll of approximately 320 people and $70 billion in damage. The vast majority of those figures are from Sandy.

It is estimated that Sandy was directly responsible for 253 fatalities across several countries, and for at least $65 billion in damage (final figure still unknown), making it second costliest storm in U.S. history, behind Hurricane Katrina’s $128 billion pricetag (adjusted for inflation). I have radar loops available for nearly all of the landfalls this season if you wanted to back and see where each of the storms affected.

Much like Katrina and Ike, Sandy’s U.S. landfall went a long way in educating the public that “there’s more to the story than the category”. That phrase refers to the other impacts that a landfalling storm has besides just the maximum sustained wind which defines the category. Any category of storm can produce tremendous flooding, and even a storm as ‘weak’ as Sandy can produce very significant storm surges and coastal erosion.

Sandy also helped to point out just how vulnerable our major coastal cities are to flooding. People continue to build and live near the water’s edge, but with that decision comes the great risk of repeated flooding and storm surge damage. We should not be so surprised when an expected outcome actually happens. Instead, we should use it as an opportunity to move people and infrastructure away from the areas of greatest risk so it’s less likely to happen next time.

Post script: It’s important to note that the tallies and statistics used here reflect the operational, real-time data, but there are often some adjustments made to intensities and tracks in a careful post-season reanalysis. The post-season reanalysis conducted by the National Hurricane Center has the advantage of hindsight and careful scrutiny of all data, without strict time constraints that the operational advisories have.

* Brian McNoldy is a senior researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

By Brian McNoldy  |  01:11 PM ET, 11/28/2012

Categories:  Latest, Tropical Weather

 
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