Forecaster revises hurricane prediction to above average
One of the leading hurricane forecasters has revised its prediction for the 2023 hurricane season, indicating that warmer than normal Atlantic sea surface temperatures will overcome the hurricane calming El Nino phenomenon.
Colorado State University is now predicting a near-average Atlantic hurricane season in 2023.
It said: "El Niño development appears certain, as water temperatures across the eastern and central tropical Pacific have anomalously warmed over the past couple of months. Tropical and subtropical Atlantic sea surface temperatures are now much warmer than normal.
"Waters across the tropical and subtropical Atlantic have anomalously warmed over the past couple of months and are near or at record levels in the eastern part of the basin. Warmer-than-normal waters in the eastern and central tropical Atlantic tend to force a weaker subtropical high that leads to weaker winds blowing across the tropical Atlantic.
"These weaker winds favour additional anomalous warming of the tropical Atlantic for the peak of the Atlantic hurricane season. The warmer-than-normal tropical Atlantic may counteract some of the increase in vertical wind shear typically associated with El Niño. The increase in sea surface temperature anomalies in the Atlantic is the primary reason for the increase in forecasted hurricane activity.
"Given the conflicting signals between a potentially robust El Niño and a much warmer than normal tropical and subtropical Atlantic, the team stresses that there is more uncertainty than normal with this outlook."
For the Pacific, Colorado State said the tropical Pacific currently has warm neutral ENSO conditions – that is, water temperatures are slightly above-normal across the eastern and central tropical Pacific. Current large-scale conditions and forecasts indicate that a transition to El Niño is virtually assured in the next couple of months.
"There remains uncertainty as to how strong El Niño will be. El Niño tends to increase upper-level westerly winds across the Caribbean into the tropical Atlantic. The increased upper-level winds result in increased vertical wind shear, which is a difference in direction and strength of winds from the lower to the upper levels of the atmosphere. Vertical wind shear can tear apart hurricanes as they try to form."
The CSU Tropical Meteorology Project team is predicting 15 named storms during the Atlantic hurricane season, which runs from June 1 to November 30. These include an unnamed sub-tropical storm in January.
CSU added: "Of those, researchers expect seven to become hurricanes and three to reach major hurricane strength (Saffir/Simpson category 3-4-5) with sustained winds of 111 miles per hour or greater.
So far, the 2023 hurricane season is exhibiting characteristics similar to 1951, 1957, 1969, 2004, and 2006, CSU said.
“Our analog seasons exhibited a wide range of outcomes, from below-normal seasons to hyperactive seasons,” said Phil 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.”
Forecasters also note that there are not many good analogs for this season, where a moderate/strong El Niño and a much warmer-than-normal Atlantic are likely to co-exist.
The team predicts that 2023 hurricane activity will be about 100 percent of the average season from 1991–2020. By comparison, 2022’s hurricane activity was about 75 percent of the average season.
The CSU team will issue another forecast update on August 3 but said it was predicting a 43% probability that a major hurricane would make landfall on the US coastline, a 21% chance for the US East Coast including the Florida peninsula, a 27% chance for for the Gulf Coast from the Florida panhandle westward to Brownsville, Texas and 47% for tracking through the Caribbean. All of these probabilities match the 140-year average.
