2021 Atlantic hurricane season forecast update
AccuWeather’s expert team of forecasters say while the 2021 hurricane season may not be as active as the 2020 season, it could be above average.
The 2021 Atlantic hurricane season has been a bit of a roller coaster ride in terms of activity through the first two-plus months of the season. At times, the basin was off the charts in terms of its production of named systems and was even briefly ahead of the record-setting pace of the historic 2020 season.
For the seventh straight year, the Atlantic produced a pre-season storm, when Ana formed as a subtropical system 200 miles northeast of Bermuda on May 22. That was followed by an active June, which resulted in three other named storms. However, since Elsa departed on July 9, the Atlantic has been in a deep slumber. In fact, the stretch from July 10 through Aug. 3 produced no named storms for the first time since 2009, according to Colorado State University Meteorologist Philip Klotzbach.
Through Aug. 10, 2020, the "I" storm, which was Isaias, had come and gone, and the frenzied pace would only continue with the development of the "J" storm, Josephine, on Aug. 13.
However, with the heart of the current season just around the corner, the Atlantic is showing serious signs of life, and AccuWeather meteorologists expect activity in the Atlantic to ramp up.
New research published earlier this year from University of Miami researcher Brian McNoldy found that there is a new normal for named tropical systems in the Atlantic based on a 30-year average from 1991 to 2020.
AccuWeather’s forecast, when compared to that 30-year average, indicates that 2021 is expected to be an above-normal season for tropical activity in the Atlantic. A normal season is considered to have 14 storms, seven hurricanes and three major hurricanes. Last year, 14 hurricanes formed, and seven of those reached the major hurricane threshold -- category 3 or higher.
As of Aug. 9, there have been five named storms. Of those, only Elsa, which was the earliest "E" named storm on record in the Atlantic, achieved hurricane status. There has yet to be a major hurricane so far in 2021, but that is likely to change when the season peaks in the weeks ahead. The peak of the season is considered to occur from mid-August to October, but forecasters caution that deadly hurricanes can occur outside that timespan.
AccuWeather‘s team of tropical weather forecasters, led by Senior Meteorologist Dan Kottlowski, says the season remains on track to produce 16-20 named storms, seven to 10 hurricanes, and three to five major hurricanes.
However, Kottlowski and his team have updated the range of direct impacts on the United States to five to seven. Previously it was three to five, but so far this season there have already been three storms that have made landfall in the U.S., which is about normal for an entire season.
Claudette moved over Louisiana on June 19, but it didn’t become a tropical storm until it moved over land, which is particularly unusual for tropical systems. That storm was followed by Danny, which was a short-lived tropical storm that made landfall over South Carolina on June 28. The third and most recent named storm to make landfall in the U.S. was Elsa, which struck northwestern Florida as a tropical storm on July 7 after turning deadly as it churned through the Caribbean days earlier.
“Due to the lull in activity the past couple of weeks, this season has not been quite as active as last year, and that should be the tone of 2021,” Kottlowski said.
This GOES-16 GeoColor satellite image taken Tuesday, July 6, 2021, at 5:50 p.m. EDT, and provided by NOAA, shows Tropical Storm Elsa in the Gulf of Mexico off the coast of Florida. (NOAA via AP)
Will La Niña return, and what does that mean for tropical development?
One of the determinants for how the season will shape up is the El Niño Southern Oscillation (ENSO). ENSO is defined simply as a short-term climate fluctuation that is determined by the warming or cooling of the waters in the central and eastern Pacific Ocean. When the water in the equatorial Pacific is warmer than average, an El Niño is typically declared. When the reverse is true, it’s known as a La Niña.
Since AccuWeather's initial forecast was released in late March, the National Weather Service's Climate Prediction Center declared on May 13 that La Niña had ended and ENSO-neutral conditions had returned to the tropical Pacific. ENSO-neutral conditions mean that water temperatures in this part of the Pacific are closer to average. The return of ENSO conditions has brought an increase in the frequency of vertical wind shear that has limited development in key areas of the basin over the past several weeks, according to Kottlowski.
However, AccuWeather’s team of long-range forecasters expects La Niña to return in September and October and continue into November as they explained in the 2021 U.S. fall forecast.
“Typically, we usually see La Niña come on about late fall to the winter season on average, but this year, it looks like it’s going to come in early just like it did last year," AccuWeather Lead Long-Range Forecaster Paul Pastelok said.
But what does the water temperature in part of the Pacific have to do with the Atlantic hurricane season?
During La Niña patterns, wind shear becomes less prevalent in the atmosphere over the Atlantic. Vertical wind shear is one of the biggest inhibitors of development for tropical systems. When there is less wind shear in the atmosphere, storms can develop with less obstruction. La Niña conditions were present during the height of 2020’s prolific season.
If La Niña returns sooner than expected, and thus brings a reduction in vertical wind shear in key development areas of the Atlantic, AccuWeather forecasters say more than 20 named storms could develop.
If more than 21 tropical storms were to develop, there could be a new first for the Atlantic. Previously, if 22 named storms formed in one season, which only happened in two hyperactive years -- 2005 and 2020 -- Greek letters were used to name tropical cyclones. The World Meteorological Organization announced in March that a supplemental name list will now be used once the designated list is exhausted.
How intense is this season shaping up to be?
AccuWeather forecasters have also bolstered the overall intensity prediction for the 2021 season. They predict the season will finish with an Accumulated Cyclone Energy (ACE) of anywhere from 130-170, up from 120-160 when the forecast was issued in late March. The 30-year ACE average for Atlantic seasons is 123. So far in 2021, the total amount of ACE is 12.8.
A jogger makes his way along Bayshore Blvd., in Tampa, Fla. as a wave breaks over a seawall, during the aftermath of Tropical Storm Elsa Wednesday, July 7, 2021. The Tampa Bay area was spared major damage as Elsa stayed offshore as it passed by. (AP Photo/John Raoux)
ACE is a metric meteorologists use to determine how intense the year is for a particular tropical basin. Although 2020 was busier than any other season on record, it wasn’t the most intense hurricane season. It produced an ACE value of 180, which is less than the 2017 season’s total of 225 and the whopping 245 from the 2005 season, according to records kept by Colorado State University researchers.
ACE doesn’t necessarily tell the whole story, Kottlowski cautioned. Just because a season has a lower ACE value than another, that doesn’t necessarily mean storms will be less damaging to the U.S.
What parts of the US remain at the highest risk?
The 2020 season brought a number of high-impact storms to the Gulf Coast and, in particular, Louisiana, which was battered by four landfalling tropical systems.
One of the reasons storms kept churning into the Gulf of Mexico was the strength and position of the Bermuda high. This high pressure area was strong last year and helped force more storms away from the Eastern Seaboard and into the Caribbean and the Gulf of Mexico.
This season, AccuWeather meteorologists believe the Bermuda high will not maintain its strength as frequently as it did in 2020, and they don’t expect it to dig as far south into the Gulf of Mexico and Caribbean. This will promote a greater chance for storms to recurve through the western Atlantic and toward the Eastern Seaboard, according to Kottlowski.
Recurving storms in the Atlantic have a greater chance of impacting the East Coast, whether due to higher-than-normal surf or landfalls along the coastline, Kottlowski explained.
Analog years serve as another data point to reference when piecing together a forecast for an entire hurricane season. Analog years are past years that featured weather similar to current and projected patterns. Forecasters will often use analog years as a way to determine future trends and predict which parts of the U.S. could face a high risk.
Several past hurricane seasons that the forecasters studied when generating this forecast were 1996, 2001 and 2012. Based on climate data from those years and similar seasons, the areas at greatest risk for direct impacts from hurricanes or tropical storms are the western and northern Gulf of Mexico, all of Florida and along the North Carolina coast, AccuWeather meteorologists say. Superstorm Sandy caused billions of dollars in damage and killed more than 145 when it slammed into the East Coast in late October of 2012.
With the peak of the season nearing, residents living in hurricane-prone areas should use any quieter periods of tropical activity to finalize hurricane safety plans, review evacuation routes and identify nearby shelters. It doesn’t take a major hurricane to cause life-altering damage to a person’s property. Even a slow-moving tropical storm has the potential to dump feet of rain and trigger life-threatening flooding, AccuWeather forecasters warn.
Editor's note: This story has been updated to reflect that four storms made landfall in Louisiana last season rather than five. A post-season analysis by the National Hurricane Center determined that Marco did not make landfall in Louisiana during August of 2020.Report a Typo