Early, Late, and Far-Flung: The Eclectic 2016 Atlantic Hurricane Season

After three relatively quiet seasons, the hurricane-generating waters of the North Atlantic, Gulf of Mexico, and Caribbean returned in 2016 to the busy production schedule they’ve maintained in most years since the mid-1990s. Assisted by the switch from a record-strong El Niño to a borderline La Niña, which reduced vertical wind shear, the 2016 season ended up above the long-term average for all of the most commonly tracked indices, with the largest number of hurricanes observed since 2012, the most major hurricanes since 2011, and the Atlantic’s first Category 5 hurricane since 2007. Persistent dryness in mid-levels of the atmosphere likely kept this season from being even more active, noted Dr. Phil Klotzbach (Colorado State University, CSU) in his end-of-season recap.

Here are the numbers for 2016 through November 30, the official last day of the Atlantic season. In parentheses are the average values for the period 1981 - 2010. Below the tally, you’ll find our look at a few noteworthy aspects of this prolonged, wide-ranging season.

Tropical cyclones (including depressions):  16
Named storms:  15 (average 12.1)
Hurricanes:  7 (average 6.4)
Major hurricanes:  3 (average 2.7)
Accumulated cyclone energy (ACE), as reported by CSU:  134 units (average 108)


Figure 1. Forecasts of the expected number of Atlantic hurricanes in 2016 as issued by a variety of forecast groups shown at the bottom of the chart. The actual total number of hurricanes through November 30 was 7, which falls within the outlooks from almost every group that issued its forecast as a range rather than a single number. Forecasts in pale blue were based on statistical models, those in red on dynamical models, and those in purple on hybrid models. Image credit: Colorado State University/Barcelona Supercomputing Center/XL Catlin.

•    The Atlantic’s deadliest hurricane in more than a decade: Matthew
The main story of the 2016 Atlantic hurricane season was Hurricane Matthew, the Atlantic’s first Category 5 storm since Felix of 2007. Matthew lasted as a major hurricane for eight days from Sept. 30 to Oct. 7, and devastated Haiti as a  Category 4 storm on October 4. Matthew killed 546 in Haiti, according to the insurance broker Aon Benfield, making it the Atlantic’s deadliest hurricane in 11 years. Damage in Haiti was estimated at $1.9 billion--a staggering 21% of the impoverished nation’s GDP, and by far Haiti’s costliest hurricane on record, according to the international disaster database, EM-DAT (previous record: $400 million 1980 dollars from Hurricane Allen.) Matthew battered Cuba as a Category 4 storm, causing $2.6 billion in damage (3.2% of their GDP.) Matthew was Cuba’s second most expensive hurricane on record, behind Hurricane Georges of 1998 ($3 billion in damage in 2016 dollars.) The Bahamas suffered $600 million in damage from Matthew (6.8% of GDP), making it their third most expensive hurricane on record behind Hurricane Frances of 2004 ($1.28 billion in losses, 2016 dollars) and Hurricane Jeanne of 2004 ($700 million in damage).

Matthew grazed the coast of Florida and Georgia before making landfall in South Carolina on October 8 as a Category 1 hurricane with 75 mph winds. Matthew’s storm surge brought water levels that were the highest ever observed along portions of the coasts of Northern Florida, Georgia and North Carolina, beating records that had been set as long ago as 1928. Near record-warm ocean waters contributed to atmospheric moisture levels that were the highest on record over portions of Florida and South Carolina as Matthew moved up the coast, allowing the hurricane to dump 1-in-1000 year rains in some areas of South Carolina and North Carolina. Matthew killed 49 people in the U.S., 28 of them in North Carolina, and U.S. damage was estimated at up to $10 billion. This would make Matthew the 17th most expensive hurricane in U.S. history. Remnant moisture from Matthew also brought flooding rains and high winds to parts of the Maritime Provinces of Canada, causing tens of millions of dollars in damage.


Figure 2.Fuel tanks are surrounded by booms to capture leaking fuel on October 12, 2016, in Lumberton, NC, in the wake of flooding from Hurricane Matthew. The Lumberton River hit an all-time record flood crest of 24.39’ on October 9, 2016. Image credit: AP/Chuck Burton.


Figure 3. Twenty-four hour rainfall amounts from Hurricane Matthew on October 6 - 10, 2016 over portions of South Carolina and North Carolina were so extreme, that one could expect them to have a recurrence interval of 1-in-1000 years based on past climatology (dark blue colors). The calculations do not incorporate general trends toward more extreme rainfall related to climate change. Image credit: NOAA/NWS.

•    A phenomenally prolonged season. On January 14, Hurricane Alex became the Atlantic’s first January hurricane since 1955. Alex maintained Category 1 strength for almost 24 hours, peaking at 85 mph winds, before weakening to a tropical storm with 65 mph winds and making landfall on January 15 on the island of Terceira in the central Azores, roughly 1000 miles west of Portugal. No major damage or casualties were reported from Alex’s landfall. Only one other time since records began in 1851 has a January tropical cyclone made landfall in the Atlantic: Hurricane Alice, which moved from northeast to southwest over the islands of Saint Martin and Saba on January 2, 1954. The only other January hurricane in the Atlantic was Hurricane One on January 4, 1938. Alex’s ascension to hurricane strength was likely aided by sea surface temperatures that were up to 1°C above average for that time of year--near 22°C (72°F.)


Figure 4. MODIS visible satellite image of Tropical Storm Alex at 9:20 am EST Friday, January 15, 2016. About an hour earlier, Alex’s western eyewall passed over the Azores island of Terceira (black outline below the center of Alex). Image credit: NASA.

The season’s other bookend (assuming no other tropical cyclones form by December 31) was deadly Hurricane Otto, the first hurricane known to make landfall on Thanksgiving Day (November 24 this year) as well as the Atlantic’s strongest hurricane on record so late in the calendar. After its landfall in far southern Nicaragua, Otto weakened to tropical storm strength while moving over northwest Costa Rica, where it killed 10 people. Only one other Atlantic tropical cyclone in recorded history has killed people later in the year: Tropical Storm Odette, whose floods killed eight people in the Dominican Republic after making landfall on December 6, 2003. Otto is the first named storm on record to pass directly over Costa Rica, and as it moved into the Pacific, it became the first tropical cyclone to keep its name while moving from one ocean basin to another. (Several other storms have successfully crossed basins, but previous policy was to change the name when this occurred.)
 
The only year with anything close to this prolonged a tropical cyclone season--January 12 to November 24--was 1938, whose activity extended from January 3 to November 10. Even if we discount January storms by arguing that they represent the tail ends of prior seasons, this year’s activity still ran from May 27 to November 24. That span is just one day shorter than the classic June-to-November season, and it’s only a month shorter than the infamous 2005 season, which went from June 8 to January 6.


Figure 5. MODIS satellite image of Otto taken at approximately 11 am EST, November 24, 2016--Thanksgiving Day. At the time, Otto was a Category 2 storm with 110 mph winds about to make landfall in Nicaragua as the strongest Atlantic hurricane ever observed so late in the year. Image credit: NASA.

•    Record amounts of oceanic fuel. The very strong 2015-16 El Niño, playing out on top of relentless long-term warming associated with human-produced greenhouse gases, led to record-warm sea surface temperatures across many parts of the globe, including the North Atlantic. Many of this year’s storms developed or intensified over waters that were 1°C - 2°C (1.8° - 3.6°F) above the local seasonal average. The widespread oceanic warmth most likely played a role in extending the season, as well as supporting greater intensification in locations and time frames where it otherwise might not have occurred. Several of this year’s hurricanes hit their peak strength near or north of 30°N, where especially warm waters prevailed during peak season.


Figure 6. Large swaths of the world’s oceans experienced record-warm sea surface temperatures for the year 2016 through October, including most of the Northwest Atlantic and Caribbean. Image credit: NOAA/NCEI.

•    A year littered with landfalls. From the first named storm to the last, 2016 saw an unusually large number of its tropical cyclones (13 out of 16) passing over or near land. Actual landfalls were also numerous, and their locations were remarkably diverse, including the Azores (Alex); South Carolina (Bonnie); Florida (Colin); Mexico (Danielle); Belize (Earl); Haiti, Cuba, The Bahamas, and South Carolina (Matthew); Bermuda (Nicole); and far south Nicaragua (Otto). Tropical Storm Julie jumped the gun on landfall by becoming a named storm while it was located over eastern Florida, making it the first tropical storm on record to develop within the Sunshine State. The five landfalling storms in the United States were the most since 2008, when six storms struck.

•    The intensity challenge, circa 2016. Over the last few years, forecasters and computer models have made some real headway in the devilishly difficult challenge of predicting rapid hurricane intensification, but 2016 gave us two humbling examples of how far we still have to go. As Hurricane Matthew drifted across the southern Caribbean Sea, it rocketed in strength from Category 1 to Category 5 in just 24 hours (from 80 mph sustained winds at 03Z on September 30 to 160 mph at 03Z on October 1). The official NHC forecast at the start of this day-long burst was for Matthew to take three days to top out at high-end Category 2 strength (105 mph). Less dramatic but still eye-opening was Nicole’s surge from Category 1 to Category 4 strength in the Northwest Atlantic over just 21 hours (from 90 mph sustained winds at 06Z on October 12 to 135 mph at 03Z on October 13). Like Matthew, Nicole had also been predicted at the start of its rapid strengthening to remain just below the major hurricane threshold (Category 3). NHC often reminds users in their discussions and statements that a particular hurricane could strengthen more rapidly than indicated in the official forecast.

•    Warning woes on the East Coast. The year’s two most significant East Coast hurricane threats, Matthew and Hermine, proved to be unusually challenging from the warning perspective. Nearly the entire East Coast from Florida to Massachusetts ended up in a hurricane or tropical storm warning as a result of the two storms. Matthew’s concave coastal track cut down on the amount of wind damage, especially in Florida, while Hermine lingered just far enough off the mid-Atlantic so that many coastal stretches from Delaware to New York that had been largely abandoned for the Labor Day weekend ended up with oddly picture-perfect weather in the midst of tropical storm warnings. In both cases, the high-end risks painted by computer forecast models were enough to justify alerting residents. Strong winds, high surf, rip tides, and coastal erosion hammered the mid-Atlantic and Northeast coast during Hermine’s leisurely decay, and Matthew’s record storm surge along the Southeast coast and its catastrophic rains inland will not soon be forgotten.


Figure 7. Waves crash ashore at Atlantic City, New Jersey, on Sunday, September 4, 2016, as Tropical Storm Hermine spins well offshore. Image credit: Jessica Kourkounis/Getty Images.

•    Florida’s hurricane “drought” is over--but another record string continues. Florida got its first hurricane landfall in nearly 11 years (3966 days) with the arrival of Category 1 Hermine, which struck the state’s northeast Gulf Coast on September 2. The landfall ended a string of good fortune unprecedented in Florida records. Hermine was also the first hurricane observed in the Gulf of Mexico since Ingrid in 2013, curtailing the Gulf’s longest hurricane-free stretch on record. Hurricane Matthew’s track just off the Southeast coast until its South Carolina landfall kept it from ending yet another remarkable “drought”: the longest period between major hurricane landfalls (Category 3 or stronger) in U.S. hurricane data going back to 1851. This ongoing stretch began after Hurricane Wilma struck Florida in October 2005. A number of observers, including Robert Hart (Florida State University) and colleagues, have noted that this record is somewhat arbitrary, especially since two large landfalling systems with lesser winds but major storm surge were the nation’s second and third most costly hurricanes on record: Sandy in 2012 and Ike in 2008, respectively. In October, Capital Weather Gang’s Jason Samenow declared the U.S. major-hurricane drought to be the “most overblown statistic in meteorology.”

Still, it’s undeniably impressive that all 29 major hurricanes recorded in the Atlantic from 2006 through 2016 managed to avoid bringing Category 3 winds to the shores of the United States. Even if this is nothing more than a fluky natural variation, the major-hurricane drought reminds us that it’s been a long time since we’ve seen what truly devastating hurricane winds can do to the nation’s Gulf and Atlantic coasts.

Addendum: Louisiana’s no-name storm
One other event deserves mention here, even though it’s not officially part of the 2016 tropical season: the slow-moving disturbance that dumped colossal amounts of rain on southern Louisiana in mid-August, causing 13 deaths and an estimated $10 - 15 billion in damage. Because surface winds were light and the surface low stayed generally onshore, the system was never declared a tropical cyclone by the National Hurricane Center. At the same time, for much of its life the storm was a symmetric warm-core low, the same type of structure associated with tropical cyclones. Regardless of its classification, the storm behaved much like other tropical depressions, tropical storms, and hurricanes that have taken their time moving through the Gulf Coast region. Some parts of Louisiana recorded more than 20" of rain in 48 hours, which qualifies as a 1-in-1,000 year rainfall event (having a 0.1 percent chance of occurring at a particular location in any given year), according to the NWS Lower Mississippi River Forecast Center. The highest rainfall total from the storm was 31.39” in Watson, Louisiana. The storm system carried near-record amounts of atmospheric moisture, drawn from the Gulf of Mexico and northwest Atlantic, where sea-surface temperatures (SSTs) were at near-record levels.

For more perspective on the 2016 Atlantic season, check out Dr. Brian McNoldy’s wrap-up (Capital Weather Gang) and Dr. Phil Klotzbach’s seasonal summary at Colorado State University. We’ll be back with a new post on Friday.

Bob Henson and Jeff Masters


Figure 8. Major flooding in Prairieville, Louisiana on Friday, August 12, 2016. Image credit: @presleygroupmk/twitter.com.