Atlantic hurricane season: How do hurricanes form?

Atlantic Hurricane Season

Some of the strongest hurricanes ever recorded have formed from tropical waves and small weather systems sweeping around the ocean. The first autumn of the Atlantic hurricane season is now on, bringing maximum activity on the waters off the coast of Florida to 0-3%, with sustained and elevated tropical storms, such as both hurricanes Florence and Michael. While tropical weather systems are often the fuel for hurricanes, they can also move quickly and interact with each other. Powerful hurricanes receive most of their energy from vertical motion (upwelling or sinking of cold Atlantic water) and strong mid-level winds (such as thunderstorms) rotating around that motion.

How does the Atlantic hurricane season work?

The Atlantic hurricane season runs from 1 August to 31 November, and runs from west to east. While this year is running well below average, it will not be producing any hurricane intensity until October. But a trough of low pressure is developing in the eastern North Atlantic that will push hurricanes further north. This cycle of minor- and major hurricanes that always follows an El Niño is expected to continue to kick off the season in October.

What does a hurricane or tropical storm look like?

While hurricanes and tropical storms can be created in many different places, they are usually formed either through a tropical wave off the coast of Africa or a tropical system that is dragged northwards by an adjacent high pressure ridge. A hurricane (Category 3, 4 or 5) is a near-seasomeness so strong that the waves and winds become huge, with ocean surface winds reaching 80-100km/h or higher. There are two main classes of hurricane with the worst categories forming as a result of interaction with warm sea surface and extremely deep warm water; these are “intense”, “extremely intense” and “extremely dangerous”. A tropical storm is a moderate intensity (Category 1, 2 or 3) with wind speeds between 74 and 95km/h and is not life-threatening.

Hurricanes develop by the weakening of thunderstorms in the atmosphere. However, sometimes the slow weakening of some rain and storm cells can trigger the formation of a tropical storm by a third generation spin, which will then grow as long as the same dynamic pattern is followed.

Can you predict hurricanes?

No. However, the Atlantic hurricane season is the only one which releases the location of hurricane formation before the storm has developed, by displaying the full range of predicted activity for five of the six months. Hurricanes do not grow out of the ground; they can form on land but to different forms and take longer to turn in the way predicted.

What can we expect from the Atlantic hurricane season?

No. Other than the forecast for an active season in October, people do not know about the changes that are happening, and how fast or slowly tropical systems are moving. We know that stronger storms are driven by the weakening of storms already on the water, so the wind speeds at the surface, mean that at least for the autumn, the prediction of an active season is for this pattern to continue.

So why is there a summer hurricane season?

Because the chances of certain systems forming just before and after the peak of the hurricane season increase when there is an El Niño, the “peak of the hurricane season”. As the head of the National Hurricane Centre, Bill Read, told Reuters: “It’s like having a king’s ransom of storms right at the end.”

More and more, the tropics have become an integral part of the world’s climate. Nature’s capriciousness – whether extreme weather or getting wetter or dryer – is linked to what we do. What we do here – in the Atlantic and in the Arctic – affects how the tropics behave. We can protect ourselves in winter by cutting our emissions, and only participate in shaping the oceans if we do the same. With a little planning and less idle chatter about climate, I believe our defences against storms have reason to hope.

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