Hurricane researchers at Colorado State University on Thursday updated their forecast for the 2021 Atlantic hurricane season, not only sticking with their prediction for an above-average season but adding one to their expected total number of named storms.
In its April 8 forecast, the CSU Tropical Meteorology Project predicted 17 total storms, including eight hurricanes, four of which were expected to be major hurricanes. Thursday the team’s forecast raised the ante to 18 total named storms, including Ana, which formed in May. Of those, the meteorology team continued to predict eight hurricanes, four of which would be Category 3 or higher on the Saffir/Simpson scale.
The National Oceanic and Atmospheric Administration issued a similar warning for an above-average season, calling for 13 to 20 named storms. And a meteorologist at the National Weather Service in San Juan, Puerto Rico, reminded residents of the Caribbean not to be concerned with predictions of how many hurricanes form between June and the end of November. Ernesto Morales encouraged islanders to be ready for any storm, because it just takes one making landfall nearby to ruin the whole summer for you.
No El Niño Increases Chance for Busy Season
In its updated forecast Thursday, the CSU team cited the likely absence of El Niño as a primary factor. Sea surface temperatures averaged across portions of the tropical Atlantic are near normal, while the subtropical Atlantic is much warmer than average. This type of sea surface temperature configuration is also considered favorable for an active 2021 Atlantic hurricane season.
Water temperatures in the tropical eastern and central Pacific are slightly below average. CSU researchers anticipate that these waters will likely remain near average for the Atlantic hurricane season. Consequently, they believe that El Niño is extremely unlike this year. El Niño tends to increase upper-level westerly winds across the Caribbean into the tropical Atlantic, tearing apart hurricanes as they try to form.
While the tropical Atlantic currently has water temperatures near their long-term averages, the warmer-than-normal subtropical Atlantic typically forces a weaker subtropical high and associated weaker winds blowing across the tropical Atlantic. These conditions then lead to warmer waters in the tropical Atlantic for the peak of the Atlantic hurricane season, the CSU update said.
18 named storms
The CSU Tropical Meteorology Project team is predicting 18 named storms in 2021, including Ana. Of those, researchers expect eight to become hurricanes and four to reach major hurricane strength (Saffir/Simpson category 3-4-5) with sustained winds of 111 miles per hour or greater. This forecast is almost identical to CSU’s initial prediction in early April, with the addition of one named storm (from 17 to 18) to include Ana’s pre-season formation.
The team said it based its forecasts on a statistical model, as well as two models that use a combination of statistical information and forecasts from dynamical models from the UK Met Office and the European Centre for Medium-Range Weather Forecasts. These models are built on 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 2021 hurricane season is exhibiting characteristics similar to 1996, 2001, 2006, 2008, 2011, and 2017.
“1996, 2008 and 2017 had above-average activity, 2001 and 2011 had near-average activity, and 2006 had slightly below-average activity,” said Phil Klotzbach, a research scientist in the Department of Atmospheric Science and lead author of the report.
The team predicts that 2021 hurricane activity will be about 120 percent of the average season. By comparison, 2020’s hurricane activity was about 145 percent of the average season. The 2020 hurricane season had six landfalling continental U.S. hurricanes, including Category 4 Hurricane Laura which battered southwestern Louisiana.
The CSU team will issue forecast updates on July 8 and August 5.
This is the 38th year that the CSU hurricane research team has issued an Atlantic basin seasonal hurricane forecast.
The report also includes the probability of major hurricanes making landfall:
– Caribbean, 58 percent (average for the last century is 42 percent)
– Entire U.S. coastline, 69 percent (average for the last century is 52 percent)
– U.S. East Coast including the Florida peninsula, 45 percent (average for the last century is 31 percent)
– Gulf Coast from the Florida panhandle westward to Brownsville, 44 percent (average for the last century is 30 percent)