The Atlantic hurricane season begins June 1 and ends November 30. Following a relatively active hurricane season in 2016, the majority of meteorological predictions forecast a near-average hurricane season for 2017. However, uncertainties regarding the prediction of the development of El Niño – one of the key variables for tropical storm formation in the Atlantic Ocean – has led to high variations among different predictions.
Meteorological extreme events such as hurricanes have the potential to generate significant onshore and offshore losses for the insurance industry. Superstorm Sandy in 2012 and Hurricane Katrina in 2005 are among the costliest events in terms of insured losses in US history. Due to the high impact of land-falling hurricanes, the AGCS Reinsurance and Catastrophe Management team annually provides an outlook of the upcoming hurricane season. This article reviews the 2016 season activity compared to predictions and provides an outlook for the upcoming 2017 hurricane season.
Hurricane Season 2016 review
The 2016 hurricane season was the costliest since 2012 and ended with 15 named storms, of which seven reached hurricane strength. Four storms reached major hurricane strength. This activity matched predictions for 2016, which forecasted an above-average activity. Seasons are rated below-, near- and above-average with respect to the historical average number of tropical storms, hurricanes and major hurricanes (Category 3 or above) over the time period 1950-2016. Category 5 Hurricane Matthew (September 28 to October 9) was the strongest and deadliest storm of 2016 with a total insured loss of $5bn. Matthew was the second costliest global loss event in 2016 after the Japan earthquake in April, which recorded loss totals of $5.5bn.
Hurricane Season 2017 outlook
The 2017 hurricane season started early with Tropical Storm Arlene (pictured above) which formed over the Atlantic Ocean on April 20. Located about 1,000 miles west of the Azores, Arlene was no threat to land. This early storm development is an anomaly and will not have an important bearing on how the 2017 Atlantic hurricane season unfolds. Furthermore, since the official opening of the season, however, Tropical Storms Bret and Cindy have formed. Bret formed in an unusual location for early storms, in the so-called “main development region” well south of the Caribbean basin, that typically sees storm development in August and September – only the third named storm to do so in June in 167 years of tracking. Early season storms generally form in the western Caribbean, as Cindy did last week. Cindy made landfall in southwestern Louisiana on June 22 and as of this writing had delivered widespread rainfall, local flashfloods, power failures, and, unfortunately, claimed the life of a 10 year-old boy vacationing with his family in Fort Morgan, Alabama. The appearance of two named storms in June occurred for only the fourth time ever, according to the Weather Channel.
Uncertainty regarding the development of El Niño
One of the phenomena impacting the frequency of hurricanes in the Atlantic Ocean is El Niño which refers to a warming of surface waters in the eastern tropical Pacific Ocean. El Niño tends to decrease hurricane activity in the Atlantic Ocean.
For the 2017 hurricane season, scientists from Colorado State University (CSU), Tropical Storm Risk (TSR) and AccuWeather predict a slightly below-average hurricane season due to the development of El Niño by the peak of the Atlantic hurricane season later this summer. Furthermore, relatively low sea surface temperatures (SST) of the North Atlantic observed in April 2017 underpin this below-average prediction. Besides providing less fuel for tropical storm formation and intensification, cooler SST are associated with a more stable atmosphere as well as drier air, both of which suppress organized thunderstorm activity necessary for hurricane development.
However, there is a high level of uncertainty regarding the prediction of El Niño formation and the estimation of the effect El Niño will have on the hurricane season. Failure of an El Niño to develop could impact the numbers of forecast storms, which is predicted by Global Weather Oscillation (GWO) and the National Oceanic and Atmospheric Administration (NOAA). GWO predicts six named storms making landfall on the mainland of the United States.
Outlook: Average Hurricane Season
The table below summarizes the predicted number of storm events for 2017 by several meteorological organizations. Regarding the predicted numbers of tropical storm events, the 2017 hurricane season is expected to be near the long term average (1950-2016), with 12 to 13 tropical storms forecasted, five to six of them reaching hurricane strength and two to three becoming major hurricanes. The predicted numbers for storm and hurricane that make landfall in the US are near or slightly above the long-term norm with three to four tropical storm and one to two hurricane landfalls. However, those predictions are associated with a higher uncertainty.
Hurricane season 2017: Predictions by institution [as of June 1, 2017]
 2015 US natural catastrophe losses curbed by El Niño; brutal North American winter caused biggest insured losses, Munich Re, 4 January, 2016.
 2016 Annual Global Climate and Catastrophe Report, Aon, January 2017.
 Cindy weakens into tropical depression after Louisiana landfall, CNN, June 22, 2017.
 Tropical Storm Cindy comes ashore in southwest Louisiana, ABC News, June 22, 2017.
 Extended range forecast of Atlantic seasonal hurricane activity and landfall strike probability for 2017. CSU, April 6, 2017.
 Pre-season forecast for North Atlantic hurricane activity in 2017, TSR, May 26, 2017.
 2017 Atlantic hurricane forecast: Possible El Niño to limit development of storms, AccuWeather, April 5, 2017.
 NOAA predicts above-average 2017 Atlantic hurricane season, The Weather Company (TWC), May 25, 2017.
 Dangerous 2017 Atlantic hurricane season predicted, GWO, February 1, 2017.
 Above-normal Atlantic hurricane season is most likely this year, NOAA, May 25, 2017.