In all, 17 named storms raked across the Atlantic Ocean basin. Ten of them became hurricanes, six of them major — rating Category 3 or higher on the Saffir-Simpson scale. The busiest and most painful stretch of the season spanned from late August to early October, when 10 hurricanes exploded over the abnormally warm tropical waters in 10 weeks.
September marked the brunt of this punishing stretch, setting a monthly record for accumulated cyclone energy or ACE, a measure of storm power and longevity. On Sept. 8, more ACE was generated than any other day in recorded history, dating to 1851. On that day, Irma was a Category 5 hurricane, Jose was a Category 4 hurricane, and Katia was a Category 2 hurricane. Maria would form just a couple of weeks later.
This season as a whole racked up the seventh-most ACE on record, joining the ranks of truly notable and memorable seasons such as 1933, 2005, 1893, 1926, 1995, 2004, 1950, 1961 and 1998.
The storms that formed this season were a magnet for land masses. Of the 17 named storms that formed, only six did not hit land. Few areas along the U.S. Gulf and Southeast coasts as well as the Caribbean were spared from at least indirect effects from the onslaught of storms.
The season’s most notorious hurricanes — Harvey, Irma and Maria — were also among the most intense, their peak winds reaching 130 mph, 185 mph and 175 mph, respectively. Mercilessly, all of them made landfall at or very close to their peak intensities. This was the first year on record that the continental United States experienced two Category 4 hurricane landfalls: Harvey and Irma.
Harvey ended the record-smashing 4,324-day-long “major hurricane drought” in the United States when it crashed ashore near Corpus Christi, Tex. And then it stalled, maintaining tropical storm status for 117 hours after landfall, a record for a Texas landfalling hurricane.
Irma will be most remembered for its horrible toll in the Caribbean, utterly destroying the island of Barbuda, shredding sections of the Virgin Islands and then knocking out power to much of Florida.
The storm maintained an intensity of 185 mph for a global record of 37 hours, and it was also the strongest hurricane on record in the Atlantic, outside of the Gulf of Mexico and Caribbean Sea. It was the most intense hurricane to ever hit the Leeward Islands, the strongest to hit Cuba since 1924, and the strongest to hit Florida since 2004. At a peak of 185 mph, it is tied for the second-strongest hurricane ever observed in the Atlantic, behind only 1980’s Allen (190 mph).
Maria formed six days after Irma’s Florida landfall and quickly developed into a monster. It intensified by about 70 mph in just 18 hours as it approached the Leeward Islands. Only three other storms in the Atlantic had more dramatic 18-hour intensification rates: Wilma (2005), Felix (2007) and Ike (2008). It crossed the Leeward Islands as a Category 5 hurricane just 13 days after Irma passed through the same area as a Category 5 hurricane and was Dominica’s first Category 5 landfall on record. It then smashed into Puerto Rico as its strongest landfalling hurricane since 1928.
All told, Bloomberg News reported that 2017’s storms comprised the most expensive U.S. hurricane season on record, producing an estimated $202.6 billion in damages.
Nearly ideal conditions in both the atmosphere and ocean give rise to the string of ferocious storms. During the peak of the season, vertical wind shear — which can disrupt storm development — was significantly lower than average right where Irma, Jose and Maria reached their peak intensities.
In addition, the tropical Atlantic Ocean was much warmer than average. When defining the tropical Atlantic as 10-20 degrees north latitude and 60-20 degrees west longitude, September sea surface temperatures were the third-warmest on record, trailing only 2005 and 2010. The usual lineup of tropical waves marching off Africa were quick to take full advantage of these hurricane-enhancing conditions as soon as they entered the region.
While Nov. 30 marks the official end of hurricane season, it is not impossible for an out-of-season storm to form in December. If any other storms form during 2017, the next name on the list is Sean. Otherwise, we start 2018 with Alberto.
Each year, the World Meteorological Organization retires from the list of storms any hurricanes that caused significant harm to life and property. From 2017’s list, the “Big 3″, Harvey, Irma and Maria, will almost certainly be removed. Possibly others too.
The last time three names were retired from a single season was 2008, and the last time more than three names were retired was 2005 (five got retired that year). Just like Igor (2010), Ike (2008) and Michelle (2001), Irma will be retired on its very first use.