CSU researchers over-predicted a near-average 2022 Atlantic hurricane season

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Jennifer Dimas
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Note to Reporters: The full verification report and a chart showing the predictions vs. observed storms are available with this news release at tropical.colostate.edu. This report includes an extensive discussion of the climate features that caused the 2022 hurricane season to end up less active than anticipated by CSU’s outlooks.

The 2022 Atlantic hurricane season ended up with near-average activity and was somewhat less active than forecasts issued by Colorado State University’s Tropical Meteorology Project.

Fourteen named storms formed in 2022, with eight of these storms becoming hurricanes and two reaching major hurricane strength. The average Atlantic hurricane season has 14 named storms, seven hurricanes and three major hurricanes.

This year, three named storms and two hurricanes made landfall in the continental United States, with Hurricane Ian striking southwest Florida as a Category 4 hurricane. Devastating storm surge, strong winds and heavy rainfall from Ian combined to cause more than $50 billion in damage and over 130 fatalities in the continental United States.

“The 2022 Atlantic hurricane season overall ended up near average. While our seasonal forecasts were close to observed values for hurricane numbers, we over-predicted other tropical cyclone metrics such as named storms, major hurricanes and Accumulated Cyclone Energy,” said Phil Klotzbach, lead author of the CSU forecast. Accumulated Cyclone Energy is an integrated metric accounting for intensity and duration of storms. Seasonal Accumulated Cyclone Energy (ACE) was approximately 75% of the 1991-2020 average.

The report summarizes all tropical cyclone activity in the Atlantic basin during the 2022 hurricane season and compares the team’s seasonal and two-week forecasts to what occurred.

A surprisingly average season

This Atlantic hurricane season was surprising given the broadly favorable large-scale conditions that were present during the season. Despite La Niña conditions prevailing throughout the season, vertical wind shear in the Caribbean and portions of the tropical Atlantic was elevated during both August and October, likely contributing to the lack of activity observed in both of those months.

Vertical wind shear was well below-average in the tropical Atlantic and Caribbean in September, favoring the above-average hurricane activity observed during that month. Historically, La Niña is associated with below-normal vertical wind shear across the tropical Atlantic and Caribbean.

The tropical Atlantic and Caribbean were warmer than normal during the hurricane season. Warm sea surface temperatures provide more fuel for developing tropical cyclones. Subtropical Atlantic sea surface temperatures were cooler than normal during August. The increased temperature gradient between the subtropical Atlantic and tropical Atlantic in August may have favored increased frontal activity and mid-latitude intrusions of dry air into the tropics in August, contributing to the lack of August tropical cyclone activity.

Recap of the season’s forecasts

CSU’s initial forecast for the 2022 season was issued on April 7 and called for an above-average hurricane season. The team predicted 19 named storms, nine hurricanes and four major hurricanes. The CSU team increased its forecast slightly on June 2, calling for 20 named storms, 10 hurricanes and five major hurricanes. CSU maintained its June outlook numbers with its July 7 update. The numbers were slightly lowered with the Aug. 4 update and called for 18 named storms, eight hurricanes and four major hurricanes. Observed activity was 14 named storms, eight hurricanes and two major hurricanes. The team predicted above-average ACE of 160 on April 8, increased their ACE forecast to 180 on both June 2 and July 7, and lowered their ACE forecast to 150 on Aug. 4. Observed ACE through Nov. 27 was 95. The 1991-2020 average Atlantic ACE was 123.

The team bases its annual forecasts on 70 years of historical data and includes factors such as Atlantic sea surface temperatures and sea level pressures, levels of vertical wind shear (the change in wind direction and speed with height), El Niño (an anomalous warming of waters in the central and eastern tropical Pacific) and other factors. While these forecast factors generally work well and explain approximately 50-60% of the year-to-year hurricane variability in these 70 years of historical data, there remains 40-50% of this variability which is not explained.

Hurricane statistics for 2022 contained in the report include:

  • 95 ACE was generated during 2022, making the 2022 Atlantic hurricane season a near-average season by the NOAA definition. This is the first Atlantic season not classified as above average (>126 ACE) since 2015.
  • The Atlantic had no named storm activity between July 3 and Aug. 31 – the first time since 1941 that the Atlantic had no named storm activity between those dates.
  • Four hurricanes (Danielle, Earl, Fiona and Ian) formed in the Atlantic between September 2-26 – the seventh time since the start of the active era (since 1995) that this has occurred. The other six years were: 1998, 2001, 2005, 2010, 2017 and 2020.
  • Hurricane Fiona, as a post-tropical cyclone, made landfall with an estimated central pressure of ~931 hPa in Nova Scotia – the lowest pressure recorded for a landfalling storm in Canada on record
  • Hurricane Ian made landfall with maximum sustained winds of 130 kt. Ian is tied with five other hurricanes for the fifth-strongest continental U.S. hurricane landfall on record, trailing only the four landfalling Category 5 continental U.S. hurricanes (Florida Keys-1935, Camille-1969, Andrew-1992, Michael-2018)
  • Hurricane Nicole was the latest calendar year hurricane to make landfall along the east coast of Florida on record.

The Tropical Meteorology Project has attributed the general upturn in major hurricane activity since 1995 as well as the earlier increase in major hurricane activity from the late 1940s through the mid-1960s to be primarily due to natural multi-decadal variability in the strength of the Atlantic Multidecadal Oscillation (AMO). A concomitant increase in several favorable hurricane-enhancing parameters occur in the tropical Atlantic during the positive phase of this oscillation, while these same parameters tend to suppress hurricanes during the negative phase of this oscillation.

A long-term trend towards La Niña, as noted by Klotzbach, Professor Michael Bell (coauthor on CSU’s seasonal hurricane forecasts) and colleagues in a recent paper may also have enhanced Atlantic activity in recent years.

The Tropical Meteorology Project, founded by the late William Gray, has been issuing forecasts for the past 39 years. The first forecast for the 2023 Atlantic hurricane season will be issued on April 13.