• A total of 18 named storms, eight hurricanes and three major hurricanes are expected this season.
  • This is above the 30-year average of 14 named storms, seven hurricanes and three major hurricanes.
  • The forecast was released Thursday by The Weather Company, an IBM company.

The 2021 Atlantic hurricane season is expected to be more active than usual, according to a perspective released April 15 by The Weather Company, an IBM company.

The outlook created by Dr. Todd Crawford, chief meteorologist at The Weather Company, forecasts 18 named storms, eight hurricanes and three major hurricanes. A major hurricane is a Category 3 or higher hurricane (winds greater than 115 mph) on the Hurricane Saffir-Simpson wind scale.

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

The outlook for the April 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 surface temperatures of the Atlantic Ocean, La Niña and other teleconnections, computer model predictions, and past seasons of hurricanes with similar weather conditions.

“While there are benefits for the season, we expect nothing to come close to last year’s activity,” said Crawford.

(AFTER: Names of the 2021 Atlantic hurricane season)

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

This forecast is similar to the April Outlook published by Colorado State University last week.

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

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 hurricane discharges each season, according to NOAA’s Hurricane Research Division.

“We forecast an above-average probability for major hurricanes to make landfall along the continental United States coast and in the Caribbean,” said Dr Phil Klotzbach, who heads the CSU Tropical Weather Project. 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 for each season, regardless of the level of activity expected. “

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

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 hit the Houston-Galveston area and caused almost as many direct deaths 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, neither hurricane nor a single tropical storm made landfall in the United States.

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

Ultimately, it’s impossible to know for sure if 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.

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.

In early spring, a La Niña was fading. NOAA’s Climate Prediction Center noted that a transition to neutral (neither El Niño nor La Niña) is likely in late spring, in time for hurricane season.

Beginning of April 2021, model-based forecast probabilities for La Niña (blue bars), neutral (gray bars) and El Niño (red bars) through end of 2021.

(IRI, NOAA / CPC)

The Niñas generally correspond 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 apart hurricanes and trying tropical systems to thrive.

This was the case in 2020, when La Niña intensified to become the strongest in 10 years. It was 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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“There is still a nice big batch of unusually warm water near Indonesia that continues to drive the signal for the tropical baseline,” Crawford said.

Sea surface temperature anomalies in March 2021 (in degrees Fahrenheit) showed the persistence of La Niña in the eastern equatorial Pacific Ocean, but also warmer-than-average water near Indonesia.

(NOAA / NNVL / NCEI)

This warm water may continue to cause upward movement and increased thunderstorm activity near Indonesia and contribute to an overall favorable atmospheric pattern for Atlantic hurricanes similar to a La Niña, even though La Niña itself is sparkling.

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

It should be noted here that the state of the Southern Oscillation El Niño (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 lead to a downward movement over at least part of the Atlantic basin, also suppressing tropical cyclones.

Other factors at play

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

Much of the waters of the Atlantic basin are already warmer than average, especially in the subtropics near Bermuda and off the northeast coast. Parts of the Gulf of Mexico are also warmer than average, with the exception of the northwestern Gulf.

Klotzbach said that current ocean temperature anomalies in the Atlantic Basin “correlate relatively well with what is generally observed during active Atlantic cyclonic seasons.”

But the heat is not as great as what we saw a year ago.

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

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Crawford particularly highlighted the Gulf of Mexico and the far eastern Atlantic Ocean near the West African coast as much cooler in April than one year ago.

But it’s not the ocean temperatures in April that will help boost or shrink tropical systems; Rather, it’s the water temperatures during hurricane season.

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

Forecast sea surface temperature anomalies (in degrees Celsius) for August-October 2021 based on the CFSv2 model, early April 2021.

(Tropicaltidbits.com)

Crawford also cited the presence of recent blocking high pressure near Greenland this spring as a factor that could also bring warmer water to the tropics during hurricane season.

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 lead to 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 come together for them to go bad, so all of those ingredients will need to be watched this year.

The Weather Company’s primary journalistic mission 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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