2024 Atlantic hurricane season set to be the most active on record
The stage is set for what could be the most active Atlantic hurricane season in recorded history. Nearly every agency that puts out a tropical forecast is calling for an above average season, some even predicting a record number of named storms.
Atlantic hurricane season officially begins on 1 June and ends on 30 November.
In an average Atlantic hurricane season, there are 14 named storms, 7 hurricanes, and 3 major hurricanes (storms reaching Category 3 strength or higher).
The National Oceanic and Atmospheric Administration (NOAA) is the main governing body to issue watches and warnings for much of the Atlantic Basin. They issue the most anticipated tropical seasonal forecasts, and this year is expected to far surpass an average year.
“The forecast for named storms, hurricanes, and major hurricanes is the highest NOAA has ever issued for the May outlook,” NOAA Administrator Rick Spinrad said at a press conference just before the season officially began.
NOAA’s official forecast called for 17-25 total named storms, 8-13 hurricanes, and 4-7 major hurricanes.
Atlantic #HurricaneSeason Outlook 2024: 85% likely. Likelihood of 17-25 named storms of which 8-13 could become hurricanes, including 4-7 major hurricanes:https://t.co/Yb8VFbdqX5@NWSCPC #HurricaneOutlook #WeatherReadyNatio pic.twitter.com/ugTih2ecsU
— NOAA (@NOAA) May 23, 2024
Colorado State University issued their very first seasonal Atlantic hurricane forecasts in 1984, making them the first entity to issue public hurricane predictions for the overall Atlantic basin. This year, they are also predicting their highest numbers ever in their initial report — 23 named storms, 11 hurricanes, and 5 major hurricanes.
The UK Met Office also issued their forecast for the upcoming season and has similar numbers of 22 total named storms, 12 hurricanes, and 4 major hurricanes.
For reference, the record for total named storms in a single year is 30 (set in 2020), and the record for the number of hurricanes is 15 (set back in 2005).
What happens when we run out of names?
There are only 21 names on the list for tropical storms in the Atlantic region, which means based off the predictions given above, it is likely we will run out of names before the season ends. So, what happens when the names run out? Prior to 2021, the Greek alphabet was used as a supplemental list. It has only been used twice: in 2005 and 2020. After Eta and Iota were ceremoniously retired in 2021 by the World Meteorological Organization, it was determined that a new supplemental list of names would be used in case the original list was depleted. If these early season predictions are anything to go by, this year might end up being the first time that new supplemental list is used.
The first named storm typically forms around June 20, with the heart of the season beginning in August and running through early October. With that said, the last nine years in a row have all had at least one named storm form before June 20, and this year could be the tenth.
“Remember it only takes one storm to devastate a community,” Spinrad said. “It’s prudent to prepare now because once the storm is headed your way it all happens so rapidly you won’t have the time to plan and prepare at that point.”
Our oceans are in hot water
One of the biggest contributing factors to the expected above average season is incredibly warm sea-surface temperatures.
Sea-surface temperatures (SST) have been record-breaking so far this year, not just globally, but particularly in the North Atlantic Basin, according to the University of Maine’s Climate Change Institute.
“Most of the models do have above normal sea surface temperatures across the entire Atlantic through the summer,” said Matt Rosencrans, NOAA’s lead for the seasonal hurricane outlook. “It’s not only favourable for more tropical activity, but it can be favourable for more extra-tropical activity as well, which means new tropical activity that forms north of 21 degrees north latitude.”
The main difference between tropical systems and extra-tropical systems are the core of the storm. Tropical systems have a warm core and extra-tropical ones have a cold core. However, the impacts these storms cause can be virtually the same: damaging winds, heavy rainfall, storm surge, etc.
“I think this season may be one of the most active hurricane seasons,” said Hiroyuki Murakami, Ph.D. Research Physical Scientist, at the NOAA Geophysical Fluid Dynamics Laboratory. “Overall, the North Atlantic is forecast to be more active this year. In that context, we may see more storms approaching Canada and also in Western Europe.”
Murakami says this doesn’t necessarily mean they are forming in the mid or high latitudes near Canada or western Europe, but rather that they are able to sustain longer due to the extremely warm sea surface temperatures.
“We know that tropical cyclones propagate northward, and this is related to tropical Atlantic sea surface temperatures,” Murakami explained. “So, in the past, when forecasting north Atlantic sea surface temperatures, the warmer it is, the more storms can go northward, because tropical cyclones can maintain their intensity longer with warmer sea surface temperatures, and also the genesis location.”
The speculation is that once formed, these tropical cyclones may be able to maintain their strength as they travel farther north, like the New England region of the US, Atlantic Canada or even western Europe.
Murakami’s recent research through the GFDL also shows that a decline in human-caused air pollution in both North America and Europe has had a surprise result: more hurricanes in the Atlantic basin.
“Essentially we find that over the past 40 years or so the aerosol emissions from the US and Europe decreased a lot,” Murakami said. “This in turn, will lead to much warmer sea surface temperatures in the North Atlantic. This can cause more storms to approach Canada and Europe.”
“Looking at the average percentage of storms entering our response zone since the inception of the Canadian Hurricane Centre (1987), we see that we get about 35% of storms that form in the basin actually enter our response zone,” says Bob Robichaud, meteorologist with the Canadian Hurricane Centre. “That percentage various, sometimes a lot, from year to year but the average since 1987 is about 35%. That translates to about 3-4 storms per year. On average about 1-2 of those will actually produce some sort of impacts on land.”
Recent analysis by Canadian Hurricane Centre meteorologists shows that for impactful/land-falling bona fide hurricanes in Canada, the 1950-2000 frequency was 2 per decade, but for the 2001-2022 time period that frequency increases to 2.5 per decade. When including storms that were hurricane-strength but not technically a hurricane at landfall (such as Fiona and Dorian) you get 3 per decade in the 1950-2000 years, but that increases to 5 per decade during the more recent 2001-2022 time period. So, while there is not a large increase, the recent uptick in numbers is certainly noteworthy.
This increase in the Canadian Maritimes region matches the trend found in Murakami’s newest research showing substantial impacts of anthropogenic climate change on tropical cyclone frequency. It highlights observed increases since 1980 near the US Atlantic coast.
La Niña's influence
Another factor that could play a role in this year’s hurricane season is the transition from El Niño to La Niña during the summer months.
“This type of environment can be more conducive for tropical cyclone development.” Spinrad said.
NOAA’s Climate Prediction Center is forecasting the development of La Niña to be pretty high (69%) during the months of July to September 2024. It is important to note though, that La Niña itself does not “create” more tropical systems, but rather just take away obstales that El Niño would have built.
“La Niña years remove any hindrance, whereas El Niño years can put in a hindrance for tropical development,” Rosencrans said.
While warm sea surface temperatures could impact the entire season, La Niña’s presence is more likely to impact the latter end of the season given that it is not expected to develop until the main season is underway.
Better communication
New this year will be changes to both the National Hurricane Center (NHC) in the US and the Canadian Hurricane Center (CHC) products.
This year the NHC will be expanding its Spanish language text products for public advisories, tropical cyclone updates and discussions, and key messages graphics in the Atlantic basin.
Additionally, changes are coming for the NHC forecast cone beginning on or around August 15. The forecast cone will now include a depiction of inland tropical storm and hurricane watches and warnings in effect for the continental United States. The reason for this change is that research has found that adding those components helps communicate inland hazards during tropical cyclone events much better, without overcomplicating the current version of the graphic.
As part of a larger Environment and Climate Change Canada (who oversees the CHC) initiative, implementation of a new comprehensive coastal flooding prediction and alerting program began in May of 2024, just in time for the start of Atlantic hurricane season.
Using new modelling techniques and the Coastal Flood Risk Index, this new flooding program will evaluate the expected impact of an event and will be assigned a risk rating ranging from low to extreme.
For both organisations, these new changes will help give early warning to emergency management organisations, citizens, and tourists about the risks from a particular storm.
About the author
Allison Chinchar is a meteorologist for CNN International, based in Atlanta.
She has covered everything from hurricanes, blizzards, flooding events and wildfires, receiving an Emmy nomination for her coverage of Hurricane Dorian that hit the Bahamas in 2019.
Allison is also a member of the American Meteorological Society, the Canadian Meteorological and Oceanographic Society, the National Weather Association, and the International Association of Broadcast Meteorology.
