Cyclone Florence gets unusual power from the warm ocean.
Other factors make this hurricane particularly violent.
Experts refer to Florence as a lesson on climate change.
By Hanno Charisius and Moritz Zajonz
One might easily get the impression that Roy Cooper, the governor of North Carolina, is prone to exaggeration when he says, "This storm is a monster, it's big and cruel." But he is not alone with his warnings. Weather and climate experts agree with him. Florence "really scares him," says Ken Graham, head of the National Hurricane Center. Long-lasting rain, life-threatening storm surges and winds – on all this, the population on the east coast of the United States in the coming days must adjust.
More than one million residents of an approximately 400-kilometer-long coastal area, especially the states of North and South Carolina, should leave their homes and custody as a precautionary measure. Hurricane Florence has been moving rapidly towards this region for several days now. On Wednesday morning, the hurricane center had driven the inhabitants of the vulnerable areas to extra hurry. Already on Thursday, the hurricane is to hit the coast.
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In order for a hurricane to reach such monstrous proportions as weather experts expect for Florence, special conditions are needed:
The ocean water that Florence is currently moving across is about 1.5 degrees Celsius warmer than normal, according to hurricane expert Brian McNoldy of the University of Miami. Even under normal circumstances, the water is warm enough at this time of the year for a storm to concoct. The heat gives the storm additional strength. In addition, warm air can absorb more water than cold and later lead to massive rainfall.
Florence is rushing towards the coast from the east. Usually hurricanes make their way to the US east coast from the south, before they usually turn off to the Atlantic. But Florence is diverted from a high-pressure ridge across the US East Coast. The last hurricane of this magnitude, which had a similar direction of movement, was Hazel's enormous destructive power in 1954.
Due to the current weather conditions, the storm slows down when it hits the coast. He could hang over North and South Carolina for days at a time, though the exact direction of the hurricane is currently uncertain. During this time he is expected to rain down huge volumes of water over the mainland. Experts expect with just under 90 centimeters of precipitation. The weather model, which correctly predicted Hurricane Harvey's 150 centimeters of rainfall last year, is forecasting 115 centimeters of water in some places over the next few days.
Florence resembles Harvey a bit "in the sense that he rushes to the coast and then comes to a screeching stop," says the professor of meteorology at the Massachusetts Institute of Technology, Kerry Emanuel. "The longer it stays, the more wind and the more rain," explains Ken Graham. That means "more trees that could fall over, more power outages".
The cyclone is not only exceptionally wet and strong, but also reaches immense proportions. Its strong tropical winds extend from the center of the hurricane in all directions over 270 kilometers – that's about the distance between Hamburg and Berlin.
However, the biggest dangers of a hurricane do not come from the wind, but from the storm tides, which can cause the Wirbelstrum. Storm surges have the potential to kill many people and great potential for destruction, the CNN broadcaster quotes the National Civil Protection Agency (FEMA). Expected rainfall could overflow rivers and cause landslides, warned the hurricane center.
Florence is also shaped by the impact of climate change. The inertia of this hurricane will be observed more frequently in storms in the future, says the climate researcher Jim Kossin of the US weather and ocean authority NOAA. Among other things, this is due to changes in the altitude winds that shift weather areas in the Earth's atmosphere.
With material from AP, DPA
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