The Life of a Cyclone

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Cyclones are the main inhabitants of the weather world. They are born and grow, make friends and part ways, reach their peak, and eventually grow old. Each one has its own character and unique path. We will talk about the unusual life of an ordinary cyclone — not a tropical one, but a cyclone from the temperate latitudes. These are rarely as powerful, yet they can spoil the weather for outdoor enthusiasts across vast territories for many days.

Infancy

The birth of a new cyclone is a true mystery. We understand this process fairly well, yet it is so complex that no single theory can fully describe it. Still, two essential conditions are always mentioned — though often phrased differently:

• Temperature contrast — when warm and cold air masses are in close proximity. This is the brain of the cyclone: without contrast, it cannot exist.
• Rising air — this is the heart of the cyclone. It takes only a slight trigger — surface heating or topographic lift — for the air to begin rising, and the heart to start beating.

Cyclones are best seen on weather maps in the form of isobars, lines of equal pressure. Air pressure is lower in the center (because the air is rising) and higher along the edges. The center is usually marked with the letter L, for «low pressure.»

As air rises in the center, air from the periphery flows in to replace it—like blood rushing to the heart. Due to the Coriolis effect, the air begins to swirl: counterclockwise in the Northern Hemisphere, and clockwise in the Southern Hemisphere.
At this moment, a cyclone is officially born.

In a cyclone, the wind not only spirals toward the center but also rotates around it — and at the very core, it rises upward. Illustration: Valeria Milovanova / Windy.app

Cyclones Maternity Hospital

Most cyclones form in specific, favorable regions—places where warm seas meet cold lands, or where the terrain creates strong temperature contrasts.

One of the most famous «maternity wards» is the North Atlantic Ocean, often called the «cyclone factory.» Here, the warm Gulf Stream encounters the cold shores of Canada and Greenland, creating ideal conditions for cyclone formation.

Cold Greenland (blue) and the warm ocean (yellow)—the perfect combination for cyclogenesis.

However, new cyclones can also be «born» from older ones—and in the Southern Hemisphere, this is almost always the case. How cute!

A small cyclone (lowercase l) is born from a large one (uppercase L).

This happens when, as a cyclone matures, the wind in certain parts begins to blow in an opposite direction to the general circulation. These areas are called waves, and it is from such «waves» that new cyclones develop.

Satellite image of an old cyclone. The hump-like wave, from which a new cyclone will soon emerge, is marked in red. Source: Nasa / Wikimedia

When a cyclone has rising air in its center, temperature contrasts between warm and cold air masses, and rotation, it can be considered fully formed.

Youth

As a young cyclone spins, the areas of temperature contrast begin to shift: cold air moves toward warm air, and warm air moves toward cold air.

An example for the Northern Hemisphere: where cold air moves southward, a cold front forms (left); where warm air moves northward, a warm front forms (right). Illustration: Valeria Milovanova

The spinning of the cyclone intensifies the upward air movements within it, and those upward movements, in turn, intensify the spinning; just like children who’ve discovered a new game, and can’t stop playing!

The cyclone grows larger, its wind speeds increase, and precipitation develops along the fronts. All this time, the cyclone is running somewhere, spoiling the weather wherever it goes.

Cyclones almost always move eastward from their birthplace, though they often veer south or north. Those coming from the south carry the most moisture and energy, bringing the heaviest precipitation and strongest winds. In summer, they cause intense thunderstorms; in winter, they bring blizzards and record snowfalls, often with heavy, wet snow that breaks power lines and knocks down trees.

Maturity

The fronts within a cyclone are constantly moving in different directions, but the cold front moves faster than the warm one. The cold front is active—it seems to run, leaping over any obstacles. The warm front, on the other hand, crawls slowly, clinging to every irregularity in its path.

It’s no surprise, then, that the cold front eventually catches up with the warm front. When they meet, they form an occluded front, which brings heavy, persistent rain. This process starts near the cyclone’s center, and gradually spreads to its outer edges.

A mature cyclone: closer to the center, the cold front has already caught up with the warm front and occlusion has appeared, though not yet at the periphery. Illustration: Valeria Milovanova

A mature cyclone: closer to the center, the cold front has already caught up with the warm front and occlusion has appeared, though not yet at the periphery.

Interestingly, some cyclones, especially in the Southern Hemisphere, can be born old, forming with an occluded front right away. Just like Benjamin Button! Yet premature aging doesn’t stop them from being some of the most powerful systems on the planet, producing hurricane-force winds and waves over 10 meters high. The Southern Ocean is even nicknamed «roaring» for its constant gales, which often reach nearby continents: South America, South Africa, Australia, and New Zealand.

In addition, mature cyclones can develop secondary cold fronts, areas with smaller temperature contrasts, behind the main cold front. These regions often have variable cloudiness with showers or drizzle. So even if the main cold front has passed, it’s still too early to relax!

A: band of clouds of the cold front, B: band of clouds on the secondary cold front, which is much weaker. Source: NERC Satellite Receiving Station / Wikimedia

Old Age

When the cold front finally overtakes the warm front everywhere, only one occluded front remains within the cyclone. There are almost no temperature contrasts left, and the heart of the cyclone stops beating.

The occlusion front (marked in purple) in old cyclones resembles a comma in shape. Source: NERC Satellite Receiving Station / Wikimedia

Most cyclones dissipate after this stage. However, if the southern part of the system suddenly warms (for instance, over land) while the northern part cools (over cold water), temperature contrasts can reappear. This process is called cyclone regeneration—its heart starts beating again, giving it a second life.

This is the life story of a typical cyclone. But why should we care? Because some forecasting errors in weather models are linked to how cyclones evolve. Models may fail to consider a cyclone’s «tendencies», or its natural behavior, and thus misjudge its path or intensity.
Stay tuned for the next article, where we’ll reveal some lesser-known facts about cyclone weather that can help you interpret forecasts more confidently!

It’s very easy to track cyclones in temperate latitudes on Windy.app! Turn on Fronts and Isobars on the map—all cyclones will be marked with the letter L. Scroll through the forecast to see how the cyclone develops: where it moves, how strong the wind will be (Wind and Wind Gusts layers), and where the heaviest precipitation is expected (Precipitation and Accumulated Precipitation layers).

To check whether the cyclone will affect your area, simply open the spot forecast. Map + spot = the most accurate forecast!

Text: Eugenio Monti, a meteorologist and a climatologist

Cover photo: Carlo / Unsplash

Read more:

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Stable and unstable atmospheric stratification

Why do cyclones rotate counterclockwise (i. e. to the left)