The Atlantic hurricane season is at its midway point but has already seen some mega-storms. Even average hurricanes release huge amounts of energy. Where does it all come from?
Those who have experienced a hurricane know the devastation one can wreak when mighty winds bear down, flattening homes, ripping up trees and creating huge storm surges. These storms are powerful. In fact, "during its life cycle a hurricane can expend as much energy as 10,000 nuclear bombs," says NASA.
Nature and Environment | 08.09.2017
At the halfway point, the 2017 Atlantic hurricane season has been defined as "very active" with seven hurricanes. Four of those seven — Harvey, Irma, Jose and Maria — have reached Category 3 or higher on the Saffir-Simpson scale. That means they are strong — very strong.
Jose was downgraded to a tropical storm, but the other three followed hot on each other's heels, causing deaths and immense destruction, when they made landfall, through flooding and wind gusts of up to 130 miles per hour (209 kilometers per hour).
Because of their destructive and deadly force, the names Irma, Harvey and Maria will be retired from use, according to Philip Klotzbach, a meteorologist specializing in Atlantic seasonal hurricane forecasts.
But where does all that force come from?
Hurricanes — or tropical cyclones — form over waters where humidity is high, sea surface temperatures are warm (more than 26 degrees Celsius) and light winds prevail. Those conditions usually occur in the summer and early autumn in the tropical North Atlantic and North Pacific.
These cyclones use "warm, moist air as fuel," according to NASA. The air moves up and away from the ocean's surface, causing an area of low air pressure to form. Air from high-pressure areas moves into the low-pressure zone. It warms and rises too.
The cycle continues, and as that warm, moist air rises and cools, the water in it forms clouds. The clouds multiply; the wind whips up and grows, continuing to be fed by the ocean's heat and water. The storm system's rotation speeds up and forms a calm area of low pressure in the center, known as the eye. The strongest winds occur outside of this in the eye wall.
Hurricanes generally weaken when they make landfall because they lose their warm water fuel. But scientists believe global warming could increase the frequency and intensity of hurricanes and tropical storms, as ocean water heats up. More warm water equals more fuel.
The most powerful hurricanes usually form in the Gulf and Caribbean, where the water is warm even in the deep sea. The Atlantic's deeper waters are typically cooler. As a hurricane grows and whips up deep, cold water, it loses fuel. This might be changing as the Atlantic heats up. Irma, for instance, had the strongest recorded winds of any hurricane to form in the open Atlantic.
Three names - one phenomenon
Hurricane, typhoon, and cyclone are actually three names for the same phenomenon. Along the North American coast they are called hurricanes, in East and Southeast Asia they are called typhoons, and near India and Australia they are called cyclones. But despite the different names, they develop in the same way.
A cyclone is created
Tropical storms develop over oceans when the water temperature is at least 26 degrees Celsius (79 degrees Fahrenheit). As the warm water evaporates and condenses, the air around it heats up and drags cooler air upwards, creating powerful winds.
The eye of the storm
The Earth's rotation causes the air stream to move around the eye of the storm, which can be up to 50 kilometers wide. This area is nearly completely free of clouds and wind.
A storm hits land
When a tropical storm hits a coastline, it becomes weaker due to the lack of warm water. In Australia, "Marcia" was soon downgraded to a category one storm, while "Lam" weakened after striking near Brisbane. Masses of water from the sea often cause the worst damage - as seen here in China after Typhoon Nanmadol in August 2011.
Hurricane Sandy was one of the strongest hurricanes ever recorded over the Atlantic Ocean. It caused waves of up to 4 meters high, fires, power outages and broken dykes. Sandy arrived with winds at speeds of more than 145 kilometers per hour. Cuba, New York and New Jersey were particularly affected.
Tornadoes however, are non-tropical whirlwinds that can occur anywhere a storm is brewing. Local temperature differences force warm air upwards and cold air down, and a column of warm air rotates upwards at an increasing velocity. Tornadoes are usually only a maximum of 1 kilometer in diameter.
As the warm air rises, it forms a funnel, the main characteristic of a tornado. Inside the funnel, the speed of the air can be tremendous - up to 500 kilometers per hour. Tornadoes are the fastest whirlwind type of weather phenomenon.
Trail of destruction
A tornado can leave a trail of destruction several kilometers long. In the US Midwest, tornadoes occur several hundred times a year, as dry, cold air from the north hits damp, warm air from the Gulf of Mexico. It's different in other countries - in Germany, for example, tornadoes occasionally occur along the coast.