Near-average storm season now projected
Following seven straight years of predicted “above-average” activity, top hurricane forecasters feel the 2023 Atlantic hurricane season will buck the trend.
In their 40th year of forecasting the upcoming hurricane season, researchers at Colorado State University are predicting a “near-average” season for the Atlantic this year — an increased description from the first report released in mid-April, which called for a “slightly below-average” season.
CSU is now forecasting there will be 15 named storms, seven hurricanes and three major hurricanes for the ’23 season, which opened on June 1. Last year, CSU predicted 19 named storms, including nine hurricanes and four major.
CSU’s Meteorology Project team anticipates the Atlantic hurricane season to be near average due to a number of factors, but uncertainty still remains.
Often used to paint a picture of the upcoming season is the El Nino Southern Oscillation (ENSO) — whether the waters in the central and eastern Pacific Ocean are warmer or cooler, typically referred to as El Nino (warmer) or La Nina (cooler).
“El Nino development appears imminent, as water temperatures across the eastern and central tropical Pacific have anomalously warmed over the past couple of months,” CSU researchers stated in their second report on June 1.
Tropical and subtropical Atlantic sea surface temperatures are now much warmer than normal.
“Current large-scale conditions and forecasts indicate that a transition to El Nino is virtually assured in the next couple of months. However, there remains uncertainty as to how strong El Nino will be,” they stated.
CSU researches stated that when waters in the eastern and central tropical and subtropical Atlantic are warmer than normal, it tends to force a weaker subtropical high and associated weaker winds blowing across the tropical Atlantic.
“These weaker winds favor additional anomalous warming of the tropical Atlantic for the peak of the Atlantic hurricane season,” CSU officials stated. “The warmer-than-normal tropical Atlantic may counteract some of the increase in vertical wind shear typically associated with El Nino. The increase in sea surface temperature anomalies in the Atlantic are the primary reason for the increase in forecasted hurricane activity.”
The CSU team bases 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, UK Met Office, Japan Meteorological Agency and Euro-Mediterranean Center on Climate Change. The models use 25 to 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 Nino (warming of waters in the central and eastern tropical Pacific) and other factors.
CSU said that thus far, the 2023 hurricane season is exhibiting characteristics similar to 1951, 1957, 1969, 2004 and 2006.
“Our analog seasons exhibited a wide range of outcomes, from below-normal seasons to hyperactive seasons,” Phil Klotzbach, research scientist in the Department of Atmospheric Science and lead author of the report, said. “This highlights the large uncertainty that exists with this outlook.”
CSU predicts this year’s hurricane activity will be about 100% of the average season from 1991-2020. By comparison, 2022’s hurricane activity was about 75% of the average season. Last year’s season will be most remembered for its two major hurricanes: Fiona and Ian, which reached a Category 5 but made landfall as a Category 4 in Southwest Florida, resulting in more than 150 fatalities and $113 billion in damage.
“It takes only one storm near you to make this an active season for you,” Michael Bell, professor in CSU’s Department of Atmospheric Science, said.
The CSU team will issue additional forecast updates on July 6 and Aug. 3.
The Tropical Meteorology Project team also includes 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.
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