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2016 Atlantic hurricane season

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Through El Niño–Southern Oscillation

The strongest, costliest, and deadliest storm of the season was Hurricane Matthew, the southernmost Category 5 Atlantic hurricane on record and the first to reach that intensity since Felix in 2007, ending the longest streak of seasons without a hurricane of such intensity in the satellite era. With at least 603 deaths attributed to it, Matthew was the deadliest Atlantic hurricane since Stan of 2005. Furthermore, damage from Matthew is estimated to be at least $16.5 billion, making it the ninth costliest Atlantic hurricane on record at the time. Hurricane Nicole became the first major hurricane to directly impact Bermuda since Hurricane Fabian in 2003, leaving widespread but relatively moderate damage on the island. The final tropical cyclone of the season – Hurricane Otto – brought severe flooding to Central America in November, particularly in Costa Rica and Nicaragua. Otto left 23 deaths and about $190 million in damage. On November 25, the storm emerged into the Eastern Pacific basin, the first such occurrence since Hurricane Cesar–Douglas in 1996. Most of the season's tropical cyclones impacted land, and nine of those storms caused loss of life. Collectively, the storms left at least 736 fatalities and $17.49 billion in damage, making the season the costliest since 2012.

Most forecasting groups predicted above average activity in anticipation of a dissipating El Niño event and the development of a La Niña, as well as warmer than normal sea surface temperatures. Overall, the forecasts were fairly accurate.

Seasonal forecasts

Ahead of and during the season, several meteorological services and scientific agencies forecast how many named storms, hurricanes, and major hurricanes will form during a season, and/or how many tropical cyclones will affect a particular country. These agencies include the Tropical Storm Risk (TSR) Consortium of the University College London, the National Oceanic and Atmospheric Administration (NOAA), United Kingdom Met Office (UKMO), Coastal Carolina University (CCU), Colorado State University (CSU), and North Carolina State University (NCSU). The forecasts include weekly and monthly changes in significant factors that help determine the number of tropical storms, hurricanes, and major hurricanes within a particular year. Some of these forecasts also take into consideration what happened in previous seasons and the predicted weakening of the 2014–2016 El Niño event. On average, an Atlantic hurricane season between 1981 and 2010 contained twelve tropical storms, six hurricanes, and two major hurricanes, with an accumulated cyclone energy (ACE) index of between 66 and 103 units. Broadly speaking, ACE is a measure of the power of a tropical or subtropical storm multiplied by the length of time it existed. Therefore, a storm with a longer duration or stronger intensity will have high values of ACE. It is only calculated for full advisories on specific tropical systems reaching or exceeding wind speeds of 39 mph (63 km/h). Accordingly, tropical depressions are not included here. After the storm has dissipated, typically after the end of the season, the NHC reexamines the data, and produces a final report on each storm. These revisions can lead to a revised ACE total either upward or downward compared to the operational value.

Pre-season forecasts

The first forecast for the year was issued by CSU on December 11, who anticipated that one of four different scenarios could occur. The scenario considered most likely was that Atlantic multidecadal oscillation (AMO) and thermohaline circulation (THC) would be stronger, but effects from El Niño would remain, resulting in a slightly above average season. The next most likely scenario was that both the AMO and THC would strengthen and the El Niño effects would cease to exist, causing a well above average season. In the other two scenarios, which were given the same probability of occurrence, the AMO and THC would weaken and the effects of El Niño would either disappear or some would remain, resulting in either a near average or well below average season.

TSR subsequently issued their first outlook for the 2016 season during December 16, 2015 and predicted that activity would be about 20% below the 1950–2015 average, or about 15% below the 2005–2015 average. Specifically they thought that there would be 13 tropical storms, 5 hurricanes, 2 major hurricanes and an ACE index of 79 units. A few months later, TSR issued their second prediction for the season during April 6, 2016 and lowered the predicted number of named storms to 12 but raised the number of hurricanes to 6. On April 14, CSU predicted that the season would be near-normal, predicting 13 named storms, 6 hurricanes and 2 major hurricanes with ACE near 93. On April 15, NCSU predicted the season would be very active, with 15–18 named storms, 8–11 hurricanes and 3–5 major hurricanes. A month later, the UKMO released its forecast, predicting a slightly above-average season with 14 named storms and 8 hurricanes. It also predicted an ACE index of 125, above the defined average ACE index at 103.

On May 27, NOAA issued its first outlook calling for a near-normal season with a 70% chance that 10–16 named storms could form, including 4–8 hurricanes of which 1–4 could reach major hurricane status. NOAA also stated that there is a 45% chance of a near-normal season, 30% chance of an above-normal season and 25% chance of a below-normal season. Also on May 27, TSR substantially increased their forecast numbers, predicting activity would be about 30% above the average with 17 named storms, 9 hurricanes, 4 major hurricanes and an ACE near 130. The reason for the increased activity forecast was the increased likelihood of La Niña forming during the season in addition to a trend towards a negative North Atlantic Oscillation, which generally favors a warmer tropical Atlantic. TSR predicted that there is a 57% chance that the 2016 Atlantic season would be above-normal, a 33% chance it would be near-normal, and only a 10% chance it would be below-normal.

Mid-season outlooks

CSU updated their forecast on June 1 to include 14 named storms, 6 hurricanes and 2 major hurricanes to include Tropical Storm Bonnie. It was again updated on July 1 to include 15 named storms, 6 hurricanes and 2 major hurricanes, to accommodate for tropical storms Colin and Danielle. On July 5, TSR released their fourth forecast for the season, slightly lowering the predicted numbers to 16 tropical storms, 8 hurricanes and 3 major hurricanes. On August 5, TSR released their final forecast for the season, lowering the numbers to 15 named storms and 7 hurricanes due to the influence of La Niña being less than anticipated previously. NOAA updated their forecast on August 11, increasing their predictions to 12–17 named storms, 5–8 hurricanes, and 2–4 major hurricanes.

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