An End to the Drought: Recap of the 2016 Hurricane Season

The Atlantic Basin

The Atlantic Basin spawns 11 named storms in an average year, six of which become hurricanes, including three that achieve major (Category 3 or higher) status. In numbers, the 2016 Atlantic hurricane season was close to this average with 15 named storms, of which seven reached hurricane strength and three became major hurricanes (Gaston, Matthew, and Nicole). But when considering losses, it was the most active and costliest since 2012.

The Atlantic hurricane season officially begins on June 1 and runs through November 30. Storms, however, can—and sometimes do—occur earlier and later in the year. On average a hurricane forms in December once every 10 years; the frequency is the same for May storms, but on rarer occasions they form even earlier. Notably, the first hurricane of 2016, Alex, formed in mid-January. Only three other tropical or subtropical storms are known to have formed this early since 1851, and only one other hurricane is known to have formed in January (in 1938).

Hurricane Drought

One of the main features of Atlantic hurricane seasons in recent years has been the absence of major (Category 3 or higher) storms making landfall on the U.S. Gulf Coast or East Coast and any hurricanes at all making landfall in Florida. These seasons were not necessarily inactive ones; rather, they were simply years in which only Category 1 or Category 2 storms made landfall in the United States, none of which struck Florida. The number of Atlantic storms that formed was close to normal each year.

According to the National Hurricane Center, about 40% of landfalling U.S. hurricanes from 1851 to 2010 made landfall somewhere along Florida’s 1,260 miles of coast. But since Wilma came ashore in south Florida in October 2005, not one of the subsequent 68 Atlantic hurricanes made landfall in the state. Upper-atmospheric steering currents pushed hurricanes such as Ike (2008), Irene (2011), Isaac (2012), and Arthur (2014) to one side of Florida or the other. Other tropical cyclones approaching the state weakened or dissipated before arriving as a result of dry air, wind shear, interaction with islands in the Caribbean, or a combination of these factors.

There was no one cause of Florida’s hurricane drought. It occurred simply because during the period of nearly 11 years the tracks of each successive hurricane managed to avoid the state. It should be noted, however, that between 2006 and June 2016, nine tropical storms made landfall in Florida. But no hurricane crossed its coast until Hermine made landfall near Tallahassee as a Category 1 storm on September 2, thus ending the longest Florida “hurricane drought” on record.

Because our understanding of the physical processes involved in hurricane activity is still incomplete—and because observational records are limited—catastrophe modelers take recourse in statistical modeling approaches. Florida’s hotly debated hurricane drought, although unprecedented in the brief historical record, is reproducible using AIR’s stochastic catalogs. (To learn more, see Suilou Huang’s blogs Notes on Florida's Hurricane 'Drought' and How Often Does Florida Experience a Hurricane Drought?)

Damaging Hurricanes

Hurricane Matthew affected the Caribbean and the southeastern coastline of the United States for nearly two weeks in September and early October. It reached its peak intensity as a Category 5 hurricane before passing between western Haiti and eastern Cuba, clipping both. It then moved along the eastern coast of the United States, weakening more quickly than anticipated to a minimal Category 1 as it bypassed Florida and Georgia before making landfall in South Carolina on October 8. Matthew did not devastate any one location, but it passed along the U.S. coast close enough and long enough to inflict a significant total of damage from wind, flooding rain, and storm surge. AIR’s estimated industry insured losses for the U.S. ranged from USD 2.2 billion to USD 6.8 billion. Even though it eventually made landfall, Matthew serves as a reminder that even bypassing storms can cause major damage.

The third and last major hurricane of the season, Nicole, had weakened from Category 4 to Category 3 when it tracked close enough to Bermuda to be termed a direct hit. According to the National Hurricane Center (NHC), only seven major hurricanes have passed within 40 nautical miles of Bermuda since records began in 1851. Nicole’s ring of strongest winds had shrunk from 50 to 40 miles in diameter when it moved over Bermuda, which is only 15 miles wide, causing numerous power outages but less damage than feared. This was the first October on record to have spawned two Category 4 or greater storms over the Atlantic Basin.

Table 1 shows the Accumulated Cyclone Energy (ACE) index as reported at the official end of the 2016 Atlantic hurricane season. The seasonal total, 132.43, is above the 1951–2000 seasonal average of 93 and is the highest since 2012. ACE-wise, 2016 was clearly above normal.