Colorado State University (CSU) hurricane researchers are expecting activity during the 2023 Atlantic hurricane season to be slightly below-average but do stress that conflicting signals between “a potentially robust El Niño and an anomalously warm tropical and subtropical Atlantic”, creates greater uncertainty than normal.
Currently, explains CSU, neutral ENSO conditions appear likely to transition to El Niño this summer or fall, although there is considerable uncertainty as to how strong an El Niño would be if it were to develop.
Typically, El Niño conditions increase upper-level westerly winds across the Caribbean into the tropical Atlantic. These winds result in vertical wind shear which can break apart hurricanes as they try to form.
However, sea surface temperatures in the eastern and central Atlantic are currently much warmer than normal, meaning that if a robust El Niño fails to happen, there’s potential for a busy Atlantic hurricane season, warns CSU.
“Larger-than-normal uncertainty exists with this outlook. We anticipate a near-average probability for major hurricanes making landfall along the continental United States coastline and in the Caribbean. As is the case with all hurricane seasons, coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them. They should prepare the same for every season, regardless of how much activity is predicted,” says CSU.
For the 2023 Atlantic hurricane season, CSU researchers are forecasting 13 named storms, six of which will reach hurricane strength, of which two are expected to become major hurricanes. This compares with the 1991 – 2020 average of 14.4 named storms, 7.2 hurricanes, and 3.2 major hurricanes. A major hurricane is category 3 strength or more, with sustained winds of 111 mph or greater.
Interestingly, the team at CSU also report on the probability of major hurricanes making landfall, which is what drives losses and therefore matters most to insurers and reinsurers.
This year, there’s a 44% probability of a major hurricane making landfall for the entire U.S. coastline, against the 1880 – 2020 average of 43%. For the U.S. East Coast, including the Florida peninsula, the probability for 2023 is 22% compared with the average of 21%. For Gulf Coast from the Florida panhandle westward to Brownsville the probability for 2023 is 28%, against a long-term average of 27%. For the Caribbean, CSU sees a 49% chance of a major hurricane landfall, compared with the long-term average of 47%.
According to CSU, the 2023 outlook is currently exhibiting characteristics similar to 1969, 2002, 2004, 2006, 2009, 2012, 2014, and 2015.
“Our analog seasons exhibited a wide range of outcomes, from below-normal seasons to hyperactive seasons. This highlights the large uncertainty that exists with this outlook,” said Phil Klotzbach, research scientist in the Department of Atmospheric Science and lead author of the report.
This is also the first year that the CSU team has introduced a new metric, accumulated cyclone energy (ACE), which is described by the team as an integrated metric accounting for storm frequency, intensity and duration. Expanding on this, CSU explains that, it is the “measure of a named storm’s potential for wind and storm surge destruction defined as the sum of the square of a named storm’s maximum wind speed for each 6-hour period of its existence.”
For the 2023 season, CSU has pegged the ACE at 100, compared with the 1991 – 2020 average of 123.
Only time will tell if an El Niño develops and how strong it might be, but the CSU team will provide future forecasts on June 1st, July 6th, and August 3rd.
This forecast from CSU follows Tropical Storm Risk’s (TSR) April forecast, in which it predicted North Atlantic hurricane activity in 2023 will be 25-30% below the 1991-2020 30-year norm, and around 20% below the long-term 1950-2022 norm.
Whether above-average or below-average, it only takes one major landfalling hurricane to drive substantial losses for the industry. Hurricane Ian will be fresh in the minds of the industry, which battered Florida in September of last year, becoming the second costliest natural catastrophe in the markets history.
