The conclusion of the 2017 Atlantic hurricane season on Nov. 30 likely comes as welcome news to those who were impacted by tropical activity in the US, Caribbean, and Central America. While individuals should take advantage of this respite in activity to rebuild devastated communities, it is never too early to start thinking about next year's hurricane season. Individuals and organizations with tropical vulnerabilities should remain vigilant and review contingency plans, particularly following the hyperactive 2017 Atlantic hurricane season.
2017 Atlantic Hurricane Season Summary
Of the 17 named systems that developed during the 2017 season, 10 reached hurricane-strength. All of the hurricanes occurred consecutively, resulting in the first back-to-back succession of 10 hurricanes since 1893. Six of the storms reached major (Category 3 or above) hurricane strength. Most notably, 2017 was the costliest hurricane season on record, with some estimates reaching over USD 365 billion. Most of this damage cost is attributed to hurricanes Harvey, Irma, and Maria which devastated parts of the US and Caribbean.
La Niña Development
It will likely take years for some countries to recover to pre-2017 status, suggesting that the 2018 Atlantic hurricane season could complicate efforts in the region to revitalize infrastructure and boost tourism. Although the official start of next year's season is six months away, current atmospheric conditions could play a role in the number and intensity of future storms. The La Niña phase of the El Niño-Southern Oscillation (ENSO) weather pattern materialized in October and early November, and is a key driver in atmospheric conditions in the tropics. During a La Niña phase, colder-than-normal sea surface temperatures occur in the central and eastern equatorial Pacific Ocean. This weather pattern reduces wind shear (defined as changing wind direction and speed throughout the atmosphere) in the Atlantic basin. Since wind shear tends to rip developing tropical systems apart, a La Niña phase of the ENSO correlates with enhanced activity in the Atlantic Ocean and Caribbean.
Forecasts indicate that, while the current La Niña event is somewhat weak, it has a strong potential to continue through at least April 2018, and possibly longer. Even if La Niña dissipates before the start of the 2018 Atlantic hurricane season on June 1, there is no guarantee that an El Niño phase (which typically correlates with reduced tropical activity) will immediately develop. It can take months for the ENSO cycle to transition between phases, meaning there is a possibility for an average or above average number of tropical systems in the Atlantic basin in 2018.
Caveats to Consider
While it is important to factor the ENSO weather pattern into seasonal forecasts, it should be noted that other teleconnections - defined as large-scale, persistent anomalies in atmospheric circulation and pressure - also play a role in tropical activity. In addition, relying too heavily on ENSO forecasts can be detrimental to predictions of tropical activity. For example, an El Niño was predicated to develop prior to the start of the 2017 hurricane season, leading some forecasters to anticipate lower than normal tropical activity. Ultimately, this ENSO phase failed to develop. Regardless of the long-term seasonal forecast, it is still important rebuild devastated communities, and begin thinking of how to best prepare for the next round of tropical systems during the off-season.
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