After making landfall twice on the Gulf Coast as a Category 1 hurricane, Nate weakened to a tropical depression and began moving inland across the U.S. South Sunday. The storm caused flooding and knocked out power to more than 100,000 people in Mississippi and Alabama, but no deaths or serious damage were reported in the region.
Here's what you need to know about Hurricane Nate 2017 and other potentially powerful storms:
Tropical Depression 19 became Tropical Storm Nate Thursday, when it savaged parts of Nicaragua, Costa Rica, and Honduras, killing at least 22 people there. As of Friday afternoon, the storm was barreling toward Mexico's Yucatan peninsula.
Nate made landfall in southeastern Louisiana before making a second landfall near Biloxi, Mississippi, overnight Sunday. Both states declared emergencies, and residents of some low-lying areas were ordered to evacuate.
The storm missed areas most hard-hit by other recent hurricanes, from Puerto Rico to Houston. It was expected to produce heavy rains and possibly tornadoes as it moved northeast Sunday. (Read about how to survive in a natural disaster.)
ROLE OF WARMER WATER
Waters over the Gulf of Mexico and Caribbean remain very warm, a condition that helps hurricanes draw strength, upping wind speeds. Due to that warmth, this hurricane season was predicted to be more active than average.
"In short: atmospheric conditions [are] hurricane-friendly, and surface sea temperatures were warmer than usual," Michael Greshko reported for us recently.
"The Climate Prediction Center says that multiple conditions, such as a strong west African monsoon, have aligned to make the Caribbean Sea and part of the tropical Atlantic—a storm-spawning area called the 'Main Development Region'—particularly well-suited to hurricanes," Greshko wrote.
And while scientists maintain that no single weather event can be attributed to climate change, two centuries of human fossil-fuel burning has altered temperatures just enough to almost certainly make this season's storms more powerful.
"In general, the way to think about it is: climate change has changed the environment that everything is happening in," Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research in Colorado, told National Geographic's Craig Welch. "When you add in the climate's natural variability and then the right conditions come along, you can get a storm which is stronger than you might otherwise have expected."
HOW HURRICANES WORK
Hurricanes form by drawing energy from warm ocean water and converting it into the mechanical energy of wind. Those that form in the Atlantic Basin—which includes the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea—are often spawned by late-summer thunderstorms that roll off the west coast of Africa near the Cabo Verde Islands.
Due to the Earth's rotation, Atlantic hurricanes rotate counter-clockwise. They are one form of tropical cyclone, which also forms in the Pacific Ocean. In the western Pacific, these same storms are known as typhoons. However, storms that form in the Southern Hemisphere rotate clockwise. (See "Typhoon, Hurricane, Cyclone: What's the Difference?")
As hurricanes form, they can be slowed, weakened, or even stopped if they pass over cool enough water, if their updraft is blocked by upper-level winds, or if too much wind shear breaks them up. The complexity of these factors, as well as the shifting nature of the winds, means their exact paths and damage capability can be difficult to predict.
This story was first published on October 5 and updated on October 8.