Seasonal outlooks generally call for a near-normal hurricane season, relative to the 1981-2010 average. The 2019 season comes after an active 2018 season with 15 named storms, including significant impacts from Hurricanes Florence and Michael. While the traditional hurricane season begins June 1 in the North Atlantic Basin, Subtropical Storm Andrea made a brief appearance roughly two weeks before the start of the season. We have seen early beginnings to a hurricane season before, and 2019 is the fifth consecutive year with a named storm before June 1.
Key Factors Contributing to Seasonal Outlooks: ENSO
The El Niño-Southern Oscillation (ENSO) is one of the most significant factors in play for a seasonal outlook. ENSO describes shifting sea-surface temperatures (SSTs) in the Tropical East Pacific, and associated large-scale weather patterns. When an El Niño is present, there are generally fewer hurricanes in the Atlantic Basin, due to stronger vertical wind shear that inhibits hurricane development. During a La Niña, wind shear is reduced and generally allows more hurricanes in the Atlantic Basin. Currently, a weak El Niño is in place and is anticipated to continue through the peak of hurricane season, with some uncertainty on strength. With all else equal, a continuing El Niño would be associated with reduced activity in the Atlantic Basin.
Key Factors Contributing to Seasonal Outlooks: Atlantic Sea Surface Temperatures
Warm SSTs are a key contributor to hurricane development. SSTs in the tropical Atlantic are currently below-average in the North Atlantic, near to slightly below-normal in the Eastern Subtropical Atlantic, and above-normal in the West Atlantic and Gulf of Mexico. With all else equal, this would contribute to near-normal activity in the Atlantic Basin at large. However, there is elevated development potential in the West Atlantic, Gulf of Mexico and Northern Caribbean. Along with possible hurricane formation in these areas, tropical systems crossing the Atlantic from Africa will also have to be monitored closely.
Basin to Landfall Volatility
Meanwhile the basin to landfall ratio for the Continental United States is highly volatile on an annual basis. Hurricane landfall is influenced by how close the hurricane is to land and steering currents in play during the hurricane lifecycle; neither of these are reliably predictable on long timescales. History reminds us of impactful hurricanes even during quiet years. Hurricane Betsy (1965) rendered severe impacts to the Northern Gulf during a season with only four observed hurricanes in the basin. Meanwhile, the 2010 season was very active with 12 hurricanes in the basin, and not a single landfall for the Continental United States.
Active tropical updates can be found at www.nhc.noaa.gov for the North Atlantic Basin. Official watches and warnings, and statements from emergency management agencies supersede this update, and should be closely followed concerning matters of personal safety.