An Active and Destructive 2018 Atlantic Hurricane Season Ends

https://www.wunderground.com/cat6/Active-and-Destructive-2018-Atlantic-hurricane-Season-Ends

Dr. Jeff Masters · November 30, 2018, 11:30 AM EST
Bob Henson contributed to this post.

Despite pre-season predictions of an average to below-average year, the 2018 Atlantic hurricane season was above average by most measures, with two U.S. hurricanes—Florence and Michael—causing unusually high death tolls and catastrophic damage in excess of $10 billion each. The 2018 tally of activity in the Atlantic was 15 named storms, 8 hurricanes, 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) index of 129. The 1981 – 2010 seasonal averages were 12.1 named storms, 6.4 hurricanes, 2.8 intense hurricanes, and an ACE of 105.6. The 15 named storms, 8 hurricanes, and ACE index of 129 this year puts 2018 in the upper third for all of these quantities since the satellite era began in 1970.

The amount of activity in 2018 stands in stark contrast to seasonal forecasts that had called for a near- or below-average season. As explained in a weather.com analysis, this was due in part to two factors: the absence of anticipated El Niño conditions, and a significant warming of the tropical Atlantic in September, near the peak of the season. A record number of subtropical storms also pushed up the total number of named storms.

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Three Category 4 hurricanes have made continental US landfall in the past two years: Harvey, Irma, and Michael. This is the first time that three Category 4 or 5 storms have made landfall on the continental U.S. in any two-year span on record. A total of 28 Category 4+ hurricanes have made a continental U.S. landfall since 1851.

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Official National Hurricane Center (NHC) track forecasts during the 2018 Atlantic hurricane season were excellent, but forecasters did not predict the full magnitude of the three major rapid intensification episodes that occurred.

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Climate change made Florence’s most intense rains over North Carolina more than 50% greater in magnitude than they would have been otherwise, according to a first-of-its-kind experimental “pre-attribution” study done as the storm was approaching landfall. Florence was also likely 8 – 9% greater in areal size due to climate change, and the storm was more likely to stay at a high Saffir-Simpson category as it approached landfall, the researchers found, using a climate model that generated forecasts with and without climate change factored in.

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Hurricane Michael made landfall at 2 pm EDT October 10, 2018 near Mexico Beach, Florida, with top sustained winds of 155 mph and a central pressure of 919 mb. Hurricane Michael’s landfall pressure was the third lowest for a continental US hurricane landfall on record, trailing only the Labor Day Hurricane of 1935 (892 mb at landfall) and Hurricane Camille of 1969 (900 mb at landfall). Hurricane Michael’s landfalling winds were the fourth highest for a continental U.S. landfall on record, trailing only the Labor Day Hurricane of 1935 (185 mph), Hurricane Camille (175 mph), and Hurricane Andrew (165 mph).

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As explained in our October post, Dangerous Rapidly Intensifying Landfalling Hurricanes Like Michael and Harvey May Grow More Common, hurricanes that happen to perform their rapid intensification just before landfall are very dangerous, since they are more likely to hit an unprepared population. Warming oceans due to human-caused climate change will cause future hurricanes to intensify at unprecedented rates, increasing the incidence of this very dangerous breed of hurricanes.

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Leslie was the latest in a series of unusual tropical cyclones that we have seen in recent years in the far Eastern Atlantic, in locations or with intensities that are extremely rare or unheard of in the historical record. In most cases, we can say that the odds of these oddball storms forming were increased by human-caused global warming, since tropical storm formation in the far Eastern Atlantic is primarily limited by cool ocean temperatures. A short list of other unusual Eastern Atlantic tropical cyclones since 2005:

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tags: extreme weather, severe weather