Tracks of all tropical cyclones during the 2018 Atlantic hurricane season. (Brian McNoldy/University of Miami)

Hurricane season officially ended Friday, and, for a second straight year, generated costly and deadly storms that ravaged the U.S. coast.

While not as active as “the hurricane season from hell” the year before, the 2018 season spawned two terrible storms in Hurricanes Florence and Michael, which will be long remembered for their devastating toll in the Carolinas and the Florida Panhandle.

Florence and its destructive rains, measured in feet, engulfed eastern North Carolina, turning interstates into rivers and communities into lakes. Fifty-three fatalities were blamed on the disaster.

Michael, with its violent 155 mph winds and storm surge over 15 feet tall, decimated the zone from Panama City to Mexico Beach. The region is still recovering and has a long rebuilding road ahead. The storm has been linked to 60 deaths.

Counting Harvey, Irma and Maria in 2017, Michael in 2018, and Typhoon Yutu last month, which smashed into the Northern Marianas (a U.S. territory), five Category 4 or stronger tropical cyclones have struck U.S. soil in the last two years, which is possibly unprecedented.

2018 marked an active Atlantic hurricane season for the third time in a row. By definition, the season begins June 1 and ends Nov. 30. This season began and ended early. Alberto, the first storm, formed in May, while Oscar, the last, came in October.

In all, 15 named storms formed, and of those, eight became hurricanes, and of those, two became major hurricanes (defined as Category 3+ on the Saffir-Simpson Wind Scale). The average numbers during a season are 12.1 named storms, 6.4 hurricanes, and 2.7 major hurricanes.

Accumulated Cyclone Energy, or ACE, is a common metric used to express the overall activity of a season, because it combines the intensities and duration of all of the storms in a simple way. The season featured above-average ACE the entire time with the exception of a 2.5-week period from Aug. 24 to Sept. 9. It ended up at 122 percent of average. While active, recall 2017′s ACE was 215 percent of average — hyperactive.


Cumulative ACE from the 2018 season (yellow) and climatology (purple). (University of Miami)

For the fourth year in a row, the season hopped off to an early start as Subtropical Storm Alberto formed on May 25. That unknowingly set the tone for what would become a season with an abnormal amount of subtropical activity.

Subtropical storms are hybrids of the storms that typically form outside the tropics (extratropical storms) and those that form in the tropics (tropical storms and hurricanes). Both tropical and subtropical cyclones are included in hurricane season statistics.

One of the most bizarre and memorable characteristics of this season is that of the 15 named storms that formed, a record seven were subtropical at some point.

The season got a huge boost during a surge of activity that spanned Sept. 1 to 16, when five named storms formed. In the heart of that period, we saw three simultaneous hurricanes on Sept. 10: Florence, Isaac and Helene. Florence would, of course, go on to strike the Carolinas, Isaac dissipated in the eastern Caribbean, and Helene tracked northward toward the Azores. Then on Sept. 12, Joyce joined the list, and there were four simultaneous named storms for the first time in a decade.


Satellite image of Hurricanes Florence, Isaac and Helene on Sept. 10. (CIRA/RAMMB)

There were only two hurricane landfalls in the entire Atlantic basin this season, and both were in the United States: Category 1 Hurricane Florence in North Carolina and Category 4 Hurricane Michael in Florida. Their landfalls were almost a month apart and were different in several important ways.

After spending almost four days as a Category 3 and 4 hurricane, Florence weakened dramatically as it approached the Carolinas, barely clinging to hurricane status. While this diminished the danger caused by wind and storm surge, the storm slowed down to a virtual stall as it came ashore so it was able to dump tremendous amounts of rain over parts of North Carolina and South Carolina.

Up to about three feet of rain fell near Wilmington. Both North Carolina and South Carolina broke their rainfall records for tropical cyclone events. This resulted in widespread devastating flooding and reinforced the point there’s more to the story than the category.


Rainfall totals from Sept. 13-19. (Southeast Regional Climate Center)

Michael, on the other hand, took a long time to cook in the western Caribbean. But once all of the ingredients fell into place, it charged into the Gulf of Mexico and exploded from a tropical depression to a Category 3 hurricane in less than three days. It continued to rapidly intensify right up until landfall when it was a borderline Category 5. It was moving at a normal speed, so rainfall was not a big problem from it, but the wind and storm surge were catastrophic.

It was the strongest hurricane to affect the Florida Panhandle on record, the second Category 4 hurricane landfall in Florida in two years, and the third Category 4 hurricane landfall on the continental United States in two years, which is a record.

As one of the strongest four hurricanes to make landfall in the United States in recorded history, Michael was truly a storm for the history books.


Infrared satellite image from the time of Hurricane Michael's landfall: Oct. 10 at 18 UTC. (CIRA/RAMMB)

The only other memorable storm from this season was Leslie. Leslie was a thorn in forecasters' sides for three weeks, and it spent most of that time meandering around the north-central Atlantic until it made a final run for Portugal as a hurricane. Leslie contributed 17 percent of the season’s ACE by itself, second only to Florence, which contributed 30 percent of the total. The storm was responsible for 16 deaths in Portugal and France.


The three-week-long meandering track of Hurricane Leslie (and tropical storm and subtropical storm). (tropicalatlantic.com)

Next year’s list of names is a repeat of the 2013 list (begins with Andrea, Barry and Chantal), but will include a new name, Imelda, to replace Ingrid, which was permanently retired after the 2013 season.