A satellite image shows Hurricane Milton bearing down on Florida.
Photo: AFP / NOAA
Milton is the latest hurricane to strike the southeastern coast of the United States, just two weeks after Hurricane Helene caused widespread devastation and killed hundreds in the area.
It is is the ninth hurricane of the 2024 Atlantic hurricane season and the fourth major hurricane (defined as a hurricane forecast to cause devastating or catastrophic damage).
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But why do so many hurricanes form during this ‘season’? When does it run until? And how does it differ throughout the world?
Here’s what you need to know.
What is hurricane season?
Hurricane season is a time of year when hurricanes (also referred to as typhoons or tropical cyclones) usually develop.
There are seven different hurricane seasons covering different parts of the globe.
The seasons usually run during the summer and autumn months in each area, when warmer seas make it more likely that damaging storms will develop.
The exception to this is the Northwest Pacific typhoon season, which runs all year round.
A resident secures aluminium shutters across windows in Dunedin, Florida, ahead of Hurricane Milton’s expected landfall.
Photo: AFP / Bryan R. Smith
When is hurricane season?
The Atlantic hurricane season – which has produced Helene and Milton – is currently in full force.
In Aotearoa, our cyclone season (the southwest Pacific cyclone season) begins in November and ends in April.
Here are the dates for each season, according to the US National Oceanic and Atmospheric Administration:
- Atlantic hurricane season: 1 June – 30 November
- Eastern Pacific hurricane season: 15 May – 30 November
- Northwest Pacific typhoon season: All year (although most typhoons develop between May and October)
- North Indian cyclone season: 1 April – 31 December
- Southwest Indian cyclone season: 31 May – 15 October
- Southeast Indian cyclone season: 15 October – 31 May
- Southwest Pacific cyclone season: 1 November – 30 April
Each season has a ‘peak’ – when cyclones or hurricanes are most likely to be formed. In the Atlantic, the peak is in early- to mid-September, while here in Aotearoa, cyclone season peaks in late February/early March.
Cyclone Gabrielle hit Aotearoa just before the cyclone season’s usual peak in late February/early March.
Photo: Leonard Powell
Why are hurricanes more likely to form during hurricane season?
Hurricanes need a specific set of meteorological ingredients to develop.
According to the US government’s National Ocean Service, these ingredients are:
- A pre-existing weather disturbance, such as a tropical wave
- Warm water (at least 26.5 degrees Celsius over a depth of 50 metres)
- Thunderstorm activity (which uses ocean heat to fuel hurricanes)
- Low wind shear (a change in wind speed or direction, which can tear hurricanes apart)
Warm water is crucial to the development of a hurricane, and that is much more likely during the summer and autumn months.
That is also the reason why colder areas, away from the equator, don’t have their own hurricane seasons.
The hurricane’s rapid intensification to a Category 5 was fueled by unusually warm water in the Gulf of Mexico. Human-driven warming is linked to stronger and more rapidly intensifying hurricanes.
— NASA Earth (@NASAEarth) October 8, 2024
Climate change also has something to do with it. Global warming has led to hotter seas, which are linked to “stronger and more rapidly intensifying hurricanes”, NASA Earth says.
Milton’s rapid intensification to a category 5 hurricane – the most severe – was “fuelled by unusually warm water in the Gulf of Mexico”, it says.
Milton’s intensity continues to fluctuate, however, and it has been downgraded to a category 4 at time of writing.
Appearing on NBC News, meteorologist John Morales broke down as he described the likely impact of the hurricane, labelling it “horrific”, and its link to climate change.
“The seas are just incredibly, incredibly hot. A record hot,” he said.
“You know what’s driving that, I don’t need to tell you: Global warming, climate change, leading to this and becoming an increasing threat.”
I debated whether to share this. I did apologize on the air. But I invite you to read my introspection on @BulletinAtomic of how extreme weather driven by global warming has changed me. Frankly, YOU should be shaken too, and demand #ClimateActionNow. https://t.co/GzQbDglsBG
— John Morales (@JohnMoralesTV) October 7, 2024
Do hurricanes form outside hurricane season?
It’s unusual, but yes.
Taking the Atlantic hurricane season as an example, about 19 in every 20 hurricanes forms between 1 June and 30 November, but US government statistics show some do fall outside that window – most commonly in May.
In the Southwest Pacific, about 96 percent of all cyclone activity falls within our season of 1 November – 30 April, according to the World Meteorological Organisation.
Off-season hurricanes or cyclones do not usually make landfall and are usually less deadly than in-season hurricanes – but that is not to say they can’t kill.
The deadliest off-season cyclone in the Southwest Pacific was Tropical Cyclone Namu in May 1986, which took more than 100 lives in the Solomon Islands.
What can New Zealand expect this cyclone season?
The northern parts of New Zealand will be at normal to higher-than-normal risk of a tropical cyclone when the season begins in a few weeks’ time.
The National Institute of Water and Atmospheric Research (Niwa) and MetService say between 0-1 cyclones are expected to affect Aotearoa between November and April.
That represents a “normal-elevated” risk level.
Between six and 10 named cyclones could hit the Southwest Pacific during the season, with nine being the long-term average, the services say.
