Warming oceans, La Nina and reduced trade winds to fuel a hyperactive hurricane season for North Atlantic

The National Oceanic and Atmospheric Administration (NOAA) of the United States and the United Kingdom’s Met Office have predicted an extremely stormy season for the North Atlantic Ocean in 2024.

Both national weather agencies blamed the intense hurricane activity on the unprecedented warming of the North Atlantic Ocean along with the impending La Nina phenomenon in the equatorial Pacific Ocean, reduced Atlantic trade winds and less wind shear. 

There is an 85 per cent chance for the formation of above-normal number of named tropical storms and hurricanes in 2024, according to NOAA’s forecast for the North Atlantic hurricane season that lasts from June 1 to November 30. There is only a 10 per cent chance of a near-normal season and 5 per cent chance of a below-normal season, it said. 

Meteorologists from NOAA predicted that there could be up to 17-25 named tropical storms with wind speeds more than 63 kilometres per hour. Out of these, eight-13 are forecast to intensify into hurricanes with wind speeds more than 119 km / hr. 

Four to seven of these hurricanes may turn into major hurricanes of categories 3 (178-208 km / hr), 4 (209-251 km / hr) or 5 ( >252 km / hr) on the Saffir-Simpson scale. 

The UK’s Met Office predicted that 22 named tropical storms are most likely to form in the North Atlantic Ocean basin. The weather agency also forecast that 12 of these storms would mostly likely become hurricanes, out of which four may become major hurricanes. 

The long-term average number of named tropical storms, hurricanes and major hurricanes for the North Atlantic Ocean for the period 1991-2020 are 14, seven and three respectively. The highest number of storms since 2014 formed in 2020, when there were 28 named tropical storms, 13 hurricanes and seven major hurricanes, according to the data from the Met Office. 

The Met Office also highlighted that the Accumulated Cyclone Energy (ACE) – measured in terms of the combined intensity and duration of all storms in the ocean basin during a season – would be 212 compared to the long-term average of 121. The highest ACE (225) since 2014 was recorded in 2017, the Met Office noted. 

“The upcoming Atlantic hurricane season is expected to have above-normal activity due to a confluence of factors, including near-record warm ocean temperatures in the Atlantic Ocean, development of La Nina conditions in the Pacific, reduced Atlantic trade winds and less wind shear, all of which tend to favor tropical storm formation,” NOAA said on its website.

The North Atlantic Ocean has experienced record-breaking temperatures since last year, including a long period of unusual intense marine heatwaves. 

The Climate Reanalyzer project of the University of Maine showed that the average daily sea surface temperatures in the ocean are tracking close to 22°C in May 2024, which is much higher than the normal. The temperatures are going to rise much higher from June onwards and peak around the end of August or early September. 

Source: Climate Reanalyzer

The El Nino phenomenon in the equatorial Pacific Ocean, which began in July 2023, is now waning and the conditions are shifting to a neutral phase, according to NOAA. The El Nino is the warmer than normal phase of the El Nino Southern Oscillation (ENSO) phenomenon and generally inhibits the formation of hurricanes in the North Atlantic. 

The La Nina, which is the cooler-than-normal phase of ENSO, promotes the formation and intensification of hurricanes in the ocean basin because of low vertical wind shear – upwardly mobile winds around a cyclones that can destabilise the top structure of the hurricane leading to its weakening and eventual dissipation. 

Most climate models indicated that La Nina conditions may develop in the equatorial Pacific Ocean around August. According to NOAA, there is a 69 per cent chance of the development of La Nina between July and September. 

Among other factors that could fuel the storms are the weak trade winds over the North Atlantic Ocean and the West African Monsoon, both of which are known to aid the formation and strengthening of hurricanes. 

NOAA further alerted: 

Human-caused climate change is warming our ocean globally and in the Atlantic basin, and melting ice on land, leading to sea level rise, which increases the risk of storm surge. Sea level rise represents a clear human influence on the damage potential from a given hurricane.

To improve its forecasts of individual hurricanes, NOAA has taken a slew of measures in 2024. Beginning from August 15, the weather agency will start issuing an experimental forecast cone graphic, which will inform on the risks faced by inland areas from a particular storm or hurricane. 

NOAA will also issue intermediate warnings and advisories for impacted populations in between its regular alert every six hours whenever it would be needed and rainfall graphic for Central America and the Caribbean, which would predict the total rainfall that is going to occur due to a storm or a hurricane in these regions.

NOAA is also going to use new tools for its forecasts such as the Modular Ocean Model which would help “improve the representation of the key role the ocean plays in driving hurricane intensity”. “Another model, SDCON, will predict the probability of tropical cyclone rapid intensification,” according to NOAA. 

Rapid intensification occurs when a tropical cyclone gains wind speeds of more than 55 kilometres per hour within a 24-hour period and it has been witnessed in many hurricanes, typhoons and cyclones in the past few years.

NOAA will also be taking additional data inputs from upgraded temperature and wind speed measuring buoys, radar mounted aircrafts, sail drones and underwater gliders throughout the North Atlantic Ocean Basin. 

“AI-enabled language translations and a new depiction of inland wind threats in the forecast cone are just two examples of the proactive steps our agency is taking to meet our mission of saving lives and protecting property,” said NOAA Administrator Rick Spinrad in a press release.