With tropical storm season now underway, and Tropical Storm Mario continuing to move northwest in the Eastern Pacific, we're taking a look at hurricanes, typhoons and tornadoes, and what the differences between them are.
Extreme weather events such as hurricanes, typhoons, and tornadoes can have devastating impacts, but they are easy to confuse with one another.
While all involve powerful winds and atmospheric instability, they differ significantly in how they form, where they occur, and the scale of their effects. Here, we explore each phenomenon in detail and explain how they develop.
However, before we get into hurricanes, typhoons and tornadoes, we need to understand something called the Coriolis effect.
READ MORE: Tornadoes in the UK: How do they differ from those in the US?
What is the Coriolis effect?
The Coriolis effect is an apparent force caused by the Earth's rotation, which deflects the path of moving air and fluids. In the northern hemisphere, this deflection is to the right, while in the southern hemisphere, it’s to the left. This phenomenon explains why winds circulate anticlockwise around low-pressure systems and clockwise around high-pressure systems in the northern hemisphere, and the reverse in the southern hemisphere.
First described by French physicist Gustave-Gaspard de Coriolis in 1835, the effect is crucial in shaping global wind patterns. A helpful analogy is a spinning playground roundabout: a ball thrown straight appears to curve due to the rotation, just like winds on Earth.
Without the Coriolis effect, air would flow directly from high to low pressure. Instead, it helps create the UK’s prevailing south-westerly winds, as air moving north from the subtropics is deflected eastward, influencing weather systems across the globe.
Now we understand the Coriolis effect, we can move on.
Hurricanes and Typhoons: Tropical Giants
Hurricanes and typhoons are regional names for the same type of storm: a tropical cyclone. These large, organised systems form over warm tropical oceans, typically between 5° and 30° latitude north or south of the equator. They require sea surface temperatures of at least 27°C, low wind shear, and sufficient distance from the equator to allow the Coriolis effect to induce rotation.
Tropical cyclones begin as clusters of thunderstorms. As warm, moist air rises, it cools and condenses, releasing latent heat that fuels further uplift. This process creates a self-sustaining system with a central area of low pressure. As the storm intensifies, it develops a calm, clear eye surrounded by a ring of intense thunderstorms known as the eyewall.
When sustained winds reach 74 mph, the system is classified as a hurricane (Atlantic and Northeast Pacific), typhoon (Northwest Pacific), or cyclone (Indian Ocean and South Pacific). These storms can span hundreds of kilometres and last for days, bringing torrential rain, storm surges, and destructive winds.
READ MORE: What is lightning and how does the Met Office monitor it?
The Brown Ocean Effect: When Storms Defy Expectations
Typically, tropical cyclones weaken after making landfall due to the loss of warm ocean water, their primary energy source. However, in rare cases, storms can maintain or even intensify over land through a phenomenon known as the brown ocean effect.
This occurs when the land surface is unusually warm and saturated with moisture, mimicking oceanic conditions. The high moisture content allows for continued evaporation and latent heat release, sustaining the storm’s energy. This effect was observed in Tropical Storm Bill (2015) and Tropical Storm Erin (2007), both of which intensified after landfall in the southern United States, leading to extreme rainfall and flooding.
Tornadoes: Localised but intense
A tornado is a rapidly rotating column of air that extends from the base of a thunderstorm to the ground. Tornadoes form in highly unstable atmospheric conditions, typically within severe thunderstorms known as supercells. These storms develop when warm, moist air near the surface meets cooler, drier air aloft, creating strong updrafts. If wind direction and speed vary significantly with height, a condition known as wind shear, a horizontal spinning effect can develop. This rotation can be tilted vertically by the storm’s updraft, forming a vortex.
As the vortex intensifies, a funnel cloud may appear. If it touches the ground, it becomes a tornado. Tornadoes can vary in size and strength, from narrow, rope-like funnels to massive, multi-vortex systems over 3 km wide with wind speeds exceeding 300 mph. Though short-lived, they can cause catastrophic damage along their narrow paths.
Tornadoes are most commonly associated with the central United States and regularly occur in an area known as Tornado Alley. However, they also occur in other parts of the world, including here in the UK, where around 30 are reported annually.
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