• Now 19 named storms, eight hurricanes and four major hurricanes are expected this season.
  • This is above the 30-year average of 14 named storms, seven hurricanes and three major hurricanes.
  • But we don’t expect anything close to what happened in 2020.

The 2021 Atlantic hurricane season is expected to be more active than usual and the latest outlook from The Weather Company, an IBM company, increases the number of storms expected.

According to Dr. Todd Crawford, chief meteorologist at The Weather Company, the outlook is increasing by one in the number of named storms and major hurricanes and now forecasts 19 named storms, eight hurricanes and four major hurricanes. A major hurricane is a category 3 or higher hurricane (winds over 115 mph) on the Saffir-Simpson hurricane wind scale.

This forecast is above the 30-year average (1991 to 2020) of 14 named storms, seven hurricanes and three major hurricanes.

Current outlook for the 2021 hurricane season from Colorado State University and The Weather Company, compared to an average 1991-2020 season.

The Weather Company’s outlook is based on a number of factors, including sea surface temperatures in the Atlantic Ocean, La Niña and other teleconnections, computer model predictions, and past hurricane seasons showing signs of similar weather conditions.

“The latest data and forecasts suggest that a slightly more aggressive forecast for 2021 is in order, although still nothing close to what happened in 2020,” Crawford said.

(AFTER: Atlantic hurricane season names 2021)

A record 30 named storms have formed during the 2020 hurricane season, of which 14 have become hurricanes.

Warmer sea surface temperature data and recent computer forecast models indicate that a slightly busier season may be ahead than expected in early April.

This forecast is similar to the April Outlook issued by Colorado State University.

Here are some questions and answers on what that prospect means.

What are forecasters looking at?

One of the ingredients that meteorologists, including those at The Weather Company and CSU, analyze ahead of the hurricane season is the water temperature of the Atlantic, the Caribbean, and the Gulf of Mexico.

Much of the waters of the Atlantic basin are already warmer than average, especially in the subtropics near Bermuda and off parts of the east coast. Parts of the Gulf of Mexico are also warmer than average, although parts of the northern Gulf are near average.

Sea surface temperature anomalies as of May 12, 2021.

Current ocean temperature anomalies in the Atlantic basin “correlate relatively well with what is typically seen during active hurricane seasons in the Atlantic,” said Dr Phil Klotzbach, who leads the project. CSU Tropical Meteorological Survey.

But the heat is nowhere near the magnitude we saw a year ago.

“Current Atlantic SSTs (sea surface temperatures), taken as a whole, are at lower levels than last year,” Crawford said.

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However, the recent elevation pattern in the North Atlantic, with blocking high pressure near Greenland, has helped increase sea surface temperatures in the Atlantic. This pattern may persist for a bit longer, which could lead to warmer water temperatures during hurricane season and higher tropical numbers, Crawford noted.

Climate models suggest that most of the pelvis, if not all of it, will be warmer than average during the height of the hurricane season.

Forecast of sea surface temperature anomalies (in degrees Celsius) for August-October 2021 from the CFSv2 model, from early May 2021.

(Tropicaltidbits.com)

Above-average numbers of tropical storms and hurricanes are more likely if temperatures in the major development region (MDR) between Africa and the Caribbean Sea are warmer than average. Conversely, below-average ocean temperatures can result in fewer tropical systems than if the waters were warmer.

Assuming atmospheric factors are favorable, the warmer waters of the MDR allow tropical waves, the forming engines that can eventually become tropical storms, to move closer to the Caribbean and the United States.

The prevalence of windshear and dry air across the Atlantic will also need to be monitored over the next six to eight months.

The amount of dry air rolling off the coast of Africa will also need to be monitored. Even though the water temperature is boiling and there is little wind shear, dry air can still disrupt the development of tropical cyclones and even prevent their birth.

Hurricanes need a fairly precise set of ingredients to fester, so all of those ingredients will need to be watched this year.

What role will La Niña play?

El Niño / La Niña, the periodic warming / cooling of the eastern and central equatorial Pacific Ocean, can alter weather patterns and influence winds in the Atlantic basin during hurricane season.

La Niña continues to fade, and the NOAA Climate Prediction Center noted that a switch to neutral (neither El Niño nor La Niña) is likely in late spring, in time for hurricane season.

Forecast probabilities based on the model in early April 2021 for La Niña (blue bars), neutral (gray bars) and El Niño (red bars) through the end of 2021.

(IRI, NOAA / CPC)

The Niñas generally corresponds to more active hurricane seasons because the cooler water in the eastern Pacific produces weaker trade winds and less wind shear in the Caribbean Sea that would otherwise tear hurricanes and trying tropical systems to develop.

This was the case in 2020, when La Niña intensified to become the strongest in 10 years. It is one of the factors behind a record 30 named storms in 2020.

But if La Niña wears off, its influence on the atmosphere may not wane in time for hurricane season.

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Warm water near Indonesia may continue to cause upward movement and increased thunderstorm activity there and contribute to a favorable overall atmospheric pattern for Atlantic hurricanes similar to a La Niña, even though the La Niña itself fizzled out.

Think of this lingering atmospheric pattern as the ghost of La Niña.

The highlighted blue area shows the disappearance of La Niña.

(NOAA / PSL)

The state of El Niño-Southern Oscillation (ENSO) is notoriously difficult to predict. This is especially true from February to May, when the “spring predictability barrier“is at stake, a period when the expected skills are lower than the rest of the year.

Despite that, El Niño is probably not on the table this season.

“Our best guess is that we probably won’t have El Niño conditions for the peak of the hurricane season in the Atlantic,” Klotzbach said.

Stronger El Niños tend to correspond to less active hurricane seasons because the warmer water in the eastern Pacific produces more shear winds and stronger low-level winds in the Caribbean Sea that can tear through hurricanes and systems that try to develop. They can also cause shipwreck movement over at least part of the Atlantic basin, also suppressing tropical cyclones.

What does this mean for the United States?

A record 11 storms made landfall in the United States in 2020, including six hurricanes: Hanna, Isaias, Laura, Sally, Delta and Zeta.

(AFTER: Laura, the entire Greek alphabet retired after the 2020 hurricane season)

That’s well above the average of one to two affected hurricanes each season, according to NOAA’s Hurricane Research Division.

“We expect an above-average probability of major hurricanes to hit the continental United States coast and the Caribbean,” Klotzbach said. As with all hurricane seasons, coastal residents are reminded that it only takes a hurricane that makes landfall to make it an active season for them. They should prepare the same way for each. season, regardless of the planned activity. “

Despite the 2020 season, there is not necessarily a strong correlation between the number of storms or hurricanes and landings in the United States in any given season. One or more of the named storms expected to develop this season may or may not hit the United States.

Some past hurricane seasons have been inactive but have included at least one notable landing.

The 1992 season produced only six named storms and one subtropical storm. However, one of those named storms was Hurricane Andrew, which devastated South Florida as a Category 5 hurricane.

In 1983 there were only four named storms, but one of them was Alicia. The Category 3 hurricane struck the Houston-Galveston area and killed almost as many people there (21) as Andrew in South Florida (26).

In contrast, the 2010 Atlantic season was very active, with 19 named storms and 12 hurricanes. Despite the high number of storms that year, no hurricane and a single tropical storm made landfall in the United States.

In other words, a season can produce many storms but have little impact, or produce few storms and have one or more that hit the US coast with a major impact.

The bottom line is that it is impossible to know for sure whether an American hurricane will occur this season. Keep in mind that even a weak tropical storm hitting the United States can have major impacts, especially if it moves slowly and its precipitation triggers flooding.

The main journalistic mission of The Weather Company is to report on the latest weather news, the environment and the importance of science in our lives. This story does not necessarily represent the position of our parent company, IBM.



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