On November 30, the Atlantic hurricane season officially ended. It was an unusual year, with fewer storms than average. However, the storms that did occur were much stronger than average. There were 13 tropical storms, of which 5 developed into hurricanes. Of these five, four were major hurricanes: one Category 4 hurricane and no less than three Category 5 hurricanes, with wind speeds exceeding 250 kilometers per hour. The average season has about 14 storms, including 7 hurricanes and 3 major hurricanes.
El Niño and the Warm Sea Water
At the start of the season, on June 1, the forecast predicted an average to slightly above-average season. This forecast is based on El Niño or La Niña, neither of which were expected this season. El Niño and La Niña refer to the warming (El Niño) or cooling (La Niña) of sea water in a region of the tropical Pacific Ocean. These temperature changes affect weather worldwide. For example, during an El Niño in the Atlantic Ocean, hurricane activity often decreases; during a La Niña, hurricane activity usually increases. Without either phenomenon, neutral conditions prevail, corresponding to an average number of hurricanes.
A second important factor for hurricane activity is the temperature of tropical sea water. Hurricanes require sea water of at least 27 degrees Celsius to form and intensify. The warmer the sea water, the more energy is available for a hurricane to strengthen. In the tropical Atlantic Ocean, the sea temperature during the 2025 hurricane season was approximately 0.5 to 1 degree Celsius above average. Locally, such as in the Caribbean Sea, temperatures were observed up to 1.4 degrees Celsius higher. This relatively small extra warmth leads to a huge increase in storm intensity.
Hurricane Melissa Was One of the Strongest Hurricanes Ever
The extremely warm sea water played a crucial role in Hurricane Melissa. This hurricane passed over Jamaica at the end of October as a Category 5 hurricane, leaving a trail of destruction. The extremely warm sea water (up to 30 degrees Celsius) above Melissa allowed the hurricane to intensify within 24 hours from a tropical storm with wind speeds of 110 kilometers per hour to a Category 4 hurricane with wind speeds of 220 kilometers per hour. In the following hours, the hurricane became even stronger, reaching wind speeds of up to 295 kilometers per hour just before landfall in Jamaica. Observations even showed that Hurricane Melissa reached wind gusts of over 400 kilometers per hour – a record-breaking wind speed never before measured in a hurricane.
Relatively Many Strong Hurricanes
Melissa was not the only strong hurricane this season. Of the five hurricanes, four reached at least Category 4 intensity, with three developing into Category 5 hurricanes. Only the 2005 hurricane season had more Category 5 hurricanes, with 4 in total. It should be noted that 2005 had 28 tropical storms in total, compared to 13 this year.
The three Category 5 hurricanes of 2025 were named Melissa, Erin, and Humberto. Humberto remained over the Atlantic Ocean and posed no threat to coastal areas. Erin, on the other hand, threatened multiple areas during its long journey over the Atlantic Ocean. When it was still a relatively weak system, the storm caused flooding on the Cape Verde Islands, resulting in nine deaths and over one hundred thousand euros in damages. On the other side of the ocean, Erin passed north of the Windward Islands. Warnings were issued for Saba and St. Eustatius, although the hurricane caused little disruption on these islands.
Another Remarkable Silence
This year was also the second consecutive year that the hurricane season experienced a remarkable lull. Between August 29 and September 16, no tropical storms formed in the Atlantic Ocean, even though this period is usually the peak of the hurricane season. This remarkable lull was caused by two factors.
First, there was strong wind at high altitudes, known as wind shear: the difference in wind speed between the surface and higher altitudes. Hurricanes typically only form in environments with low wind shear. When wind shear is high, as during this period from late August to mid-September, storms are disrupted and cannot develop into hurricanes.
Second, there was a lot of dry air over the Atlantic Ocean during this period. Hurricanes need warm, moist air, and dry air can effectively suffocate a storm.
In the second half of the hurricane season, after this remarkable lull, seven storms formed within one and a half months, including Category 4 hurricane Gabrielle and Category 5 hurricanes Humberto and Melissa. Last year, when we also had a similar remarkable lull between mid-August and mid-September, we saw a similarly very active second half of the season. This season again showed that the lull did not signal the end of the season.
The fact that this lull occurred twice in a row is remarkable. This raises the question of whether this is coincidence or part of a larger trend, possibly influenced by climate change. We do not yet have the answer; research will have to determine whether we will see such remarkable seasons more often in the future.
