The first Colorado State University forecast for the 2023 Atlantic Basin hurricane season was issued Thursday and forecast slightly below average activity.
The university's Tropical Weather & Climate Research section issues an initial hurricane prediction annually prior to the official start of the season on June 1.
"We anticipate that the 2023 Atlantic basin hurricane season will have slightly below average activity," the CSU forecast release said. "Current neutral ENSO conditions look fairly likely to transition to El Niño this summer/fall. However, there is considerable uncertainty as to how strong an El Niño would be, if it does develop. Sea surface temperatures in the eastern and central Atlantic are much warmer than normal, so if a robust El Niño does not develop, the potential still exists for a busy Atlantic hurricane season."
The forecast, the result of CSU researchers Philip J. Klotzbach, Michael M. Bell, and Alexander J. DesRosiers, also said larger-than-normal uncertainty exists with the 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."
The forecast was issued in memory of William M. Gray, a renowned hurricane researcher at Colorado State University who died at the age of 86 on April 16, 2016.
The CSU forecast explained that El Niño tends to increase upper-level westerly winds across the Caribbean into the tropical Atlantic with the increased upper-level winds resulting in vertical wind shear which can tear apart hurricanes as they try to form.
The forecast said that when waters in the eastern and central tropical and subtropical Atlantic are warmer than normal, this tends to force a weaker subtropical high and associated weaker winds blowing across the tropical Atlantic with those conditions leading to warmer waters in the tropical Atlantic for the peak of the Atlantic hurricane season.
"The anomalously warm eastern and central tropical and subtropical Atlantic favor an above-normal season," researchers at CSU said. "Given the conflicting signals between a potentially robust El Niño and an anomalously warm tropical and subtropical Atlantic, the team stresses that there is more uncertainty than normal with this outlook."
Thirteen named storms
The CSU Tropical Meteorology Project team is predicting 13 named storms during the Atlantic hurricane season, which runs from June 1 to November 30.
Of those, researchers expect six to become hurricanes and two to reach major hurricane strength (Saffir/Simpson category 3-4-5) with sustained winds of 111 miles per hour or greater.
The team bases its forecasts on a statistical model, as well as four models that use a combination of statistical information and model output from the European Centre for Medium-Range Weather Forecasts, the UK Met Office, the Japan Meteorological Agency, and the Centro Euro-Mediterraneo sui Cambiamenti Climatici.
These models use 25–40 years of historical hurricane seasons and evaluate conditions including: Atlantic sea surface temperatures, sea level pressures, vertical wind shear levels (the change in wind direction and speed with height in the atmosphere), El Niño (warming of waters in the central and eastern tropical Pacific), and other factors.
So far, the 2023 hurricane season is 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,” said Klotzbach, research scientist in the Department of Atmospheric Science and lead author of the report. “This highlights the large uncertainty that exists with this outlook.”
The team predicts that 2023 hurricane activity will be about 80 percent of the average season from 1991–2020.
By comparison, 2022’s hurricane activity was about 75 percent of the average season. The 2022 hurricane season will be most remembered for its two major hurricanes: Fiona and Ian.
Fiona brought devastating flooding to Puerto Rico before causing significant surge, wind and rain impacts in the Atlantic Provinces of Canada as a post-tropical cyclone.
Ian made landfall as a Category 4 hurricane in southwest Florida, causing over 150 fatalities and $113 billion dollars in damage.
In addition to the various hurricane metrics that CSU has forecast for many years, the forecast team is introducing a new metric this year — Accumulated Cyclone Energy (ACE) occurring west of 60°W. ACE is an integrated metric accounting for storm frequency, intensity and duration. ACE generated west of 60°W correlates better with landfalling storms in the Atlantic basin than basinwide ACE.
Generally, a slightly lower percentage of basinwide ACE occurs west of 60°W in El Niño years, and since the team favors El Niño as the most likely outcome in 2023, the percentage of basinwide ACE occurring west of 60°W is slightly lower this year.
Further forecasts
The CSU team will issue forecast updates on June 1, July 6 and August 3.
This is the 40th year that the CSU hurricane research team has issued an Atlantic basin seasonal hurricane forecast. The Tropical Meteorology Project team also includes Michael Bell, professor in the CSU Department of Atmospheric Science and Alex DesRosiers, a PhD candidate in the same department. Bill Gray, who originated the seasonal forecasts, launched the report in 1984 and continued to author them until his death in 2016.
The CSU forecast is intended to provide a best estimate of activity in the Atlantic during the upcoming season – not an exact measure. As always, the researchers caution coastal residents to take proper precautions.
“It takes only one storm near you to make this an active season for you,” Bell said.
Landfalling probability included in report
The report also includes the probability of major hurricanes making landfall:
- 44 percent for the entire U.S. coastline (average from 1880-2020 is 43 percent)
- 22 percent for the U.S. East Coast including the Florida peninsula (average from 1880- 2020 is 21 percent)
- 28 percent for the Gulf Coast from the Florida panhandle westward to Brownsville (average from 1880-2020 is 27 percent)
- 49 percent for the Caribbean (average from 1880-2020 is 47 percent)
The forecast team also provides probabilities of named storms, hurricanes and major hurricanes tracking within 50 miles of each county or parish along the Gulf and US East Coast, as well as hurricane-prone coastal states, Mexican states, Canadian provinces and countries in Central America and the Caribbean.
These probabilities for regions and countries are adjusted based on the current seasonal forecast. Funding for this year's report has been provided by Ironshore Insurance, the Insurance Information Institute, Weatherboy, Insurance Auto Auctions, First Onsite and a grant from the G. Unger Vetlesen Foundation.
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