Weather Bee | Record ocean temperatures fuel unprecedented hurricane activity in Florida

Oct 12, 2024 08:00 AM IST

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Warm waters in the Atlantic Ocean and cooler conditions in the Pacific are driving Florida's back-to-back hurricanes

Back-to-back hurricanes have hit the state of Florida in the United States in the past two weeks. Others – although the threat of them falling on land is not concrete now – could also be in the offing. This might appear strange when a La Niña is yet to start, which usually allows a busy hurricane season in the Atlantic Ocean. So, what is making the hurricane season busy? HT’s analysis shows that this could be because the Atlantic Ocean is very warm while the equatorial Pacific Ocean is undergoing a periodic cooling down.

TOPSHOT - A drone image shows a flooded street due to Hurricane Milton in Siesta Key, Florida, on October 10, 2024. At least four people were confirmed killed as a result of two tornadoes triggered by Hurricane Milton on the east coast of the US state of Florida, local authorities said Thursday. (Photo by Miguel J. Rodriguez Carrillo / AFP)(AFP)

Whether or not Atlantic Ocean hurricane season is busy depends on a number of factors. A key factor is warm waters in the Atlantic and relatively cool waters in the Pacific Ocean. In simple terms, this combination allows storms forming in the Atlantic to form, travel, and intensify without much obstruction from trade winds. This is usually expected during a La Niña, which appears to be arriving later than earlier forecast. However, as HT had earlier reported, a La Niña appeared imminent in September.

While a La Niña may yet be on its way, the combination of a warm Atlantic Ocean, and a relatively cool Pacific Ocean was present in September, as the accompanying map shows. The equatorial Pacific Ocean, particularly the part used to track El Niño and La Niña (5N-5S, 170W-120W or the Niño 3.4 region), had turned cooler than normal, while the Atlantic Ocean was warmer than normal.

Deviation of September sea surface temperatures from 1991-2020 mean(Abhishek Jha)

To be sure, the concern with the hurricanes in Florida was not just that they had arrived late in the season, but also their intensity. What is the reason for their intensity? The short answer is a record warming in the Atlantic Ocean. Not only was the North Atlantic Ocean warmer than normal in September, but the month was also the warmest on records for large parts of the ocean.

Anomalies and extremes in sea surface temperature in September 2024(C3S/ECMWF)

Why is the Atlantic Ocean so warm? Long-term global warming is one reason, and the one that is going to be responsible for future changes. However, the ocean has also experienced an upward bump in temperatures in recent years. Scientists have offered more than one explanation for this since last year. While some of those reasons are particular to a point in time (for example, the lack of Saharan dust that has a cooling effect on the ocean was cited as a reason last summer), there is another more permanent factor. The International Maritime Organisation imposed restrictions on the use of sulphur in marine fuels in 2020. While this prevents air pollution, the lack of pollution has also allowed the ocean surface to receive sunlight without hindrance.

Therefore, there has been a big uptick in Atlantic’s SSTs in recent years. Combined with long-term warming, this implies that hurricanes are going to be more powerful. Warmer oceans contain more energy and allow hurricanes to wreak the kind of destruction they have in Florida.

Abhishek Jha, HT’s assistant editor-data, analyses one big weather trend in the context of the ongoing climate crisis every week, using weather data from ground and satellite observations spanning decades.