Hurricanes are one of nature's most powerful natural hazards. Jenni Evans of Pennsylvania State University and Jeff Donnelly from the Woods Hole Oceanographic Institution are studying how hurricanes form and what factors influence where and when they make landfall in an effort to save lives. "When Nature Strikes" is produced by NBC Learn in partnership with the National Science Foundation and The Weather Channel. For a classroom activity related to this video, please click the Links section below.
When Nature Strikes -- Hurricanes
MARSHALL SHEPHERD reporting:
Hurricanes are one of nature’s most powerful natural hazards. With winds exceeding 100 miles per hour and a devastating storm surge, these violent storms can cause widespread destruction, which is why accurate hurricane forecasting is vital to saving lives. Two scientists funded by the National Science Foundation are helping improve some of the most challenging aspects of hurricane forecasting-- predicting a storm’s path and its intensity.
Early on the morning of August 29, 2005, Hurricane Katrina strikes the city of New Orleans, Louisiana. With maximum sustained winds of 125 miles per hour at landfall, the Category 3 hurricane pounded the region for hours, destroying buildings and homes, and unleashing floodwaters that submerged almost the entire 9th Ward. More than 1,800 people lost their lives in the disaster, with more than $100 billion in damage. Incredibly, the devastation might have been even worse, if not for the ability of meteorologists to predict Katrina's path.
JENNI EVANS (Pennsylvania State University): We understand the impacts. We understand when you should get out of the way. We also understand very well, although not perfectly, how they move.
SHEPHERD: Meteorologist Jenni Evans of Pennsylvania State University is studying some of the most crucial elements of hurricane forecasting, not just where the storm is headed, but how strong it will be when it makes landfall. Atlantic hurricanes typically form off the western coast of Africa, or over tropical ocean waters of the mid-Atlantic Ocean, Caribbean Sea, or Gulf of Mexico. When air warms and moistens due to contact with tropical ocean water, it rises from the surface creating a low pressure zone.
New air moves in to take the place of the rising air, causing the pressure to continue lowering, the winds to increase, and clouds to grow. As this process continues, pressure lowers rapidly and the winds rotate around the new storm center. When the storm reaches hurricane intensity a defined center, or eye, becomes visible.
EVANS: It’s what we call a heat engine. So a hurricane is taking warm ocean waters and converting them into clouds, and the clouds create the energy to run the hurricane
SHEPHERD: In order to forecast the storm's path, especially where the storm will make landfall, Evans turns to math and statistics by using a technique called path clustering. Taking a large group of forecasts from a number of different sources, Evans groups them by their similarities, forming track clusters. Using statistical analysis, the clusters can provide a more accurate picture of the likely path a hurricane will take and what its intensity will be when it gets there.
EVANS: We might have a whole fan of forecasts of where the storm might go. But the path clustering says well really there are three or four possible ways the atmosphere is going to evolve.
SHEPHERD: Surprisingly, another major tool in forecasting hurricane intensity involves looking at hurricanes of the past, even the distant past.
JEFF DONNELLY (Woods Hole Oceanographic Institution): One of the layers of the base here is actually from the 1635 Great Colonial Hurricane.
SHEPHERD: Paleoclimatologist Jeff Donnelly and his team at Woods Hole Oceanographic Institution in Massachusetts are looking for evidence of hurricanes buried deep underground in areas along the coast. Using a technique called coring, Donnelly takes soil samples from the bottom of nearby ponds in order to see the history of sedimentary deposits.
DONNELLY: It’s basically like a time capsule. There’s a little bit of sediment that’s deposited each year.
SHEPHERD: Over time, the deposits form in layers, providing a climate record, including clues of major weather events. The most recent deposits sit on the top of the core, the oldest on the bottom. Using the data from these core samples, Donnelly is able to reconstruct the geologic history as far back as 2,000 years. Studying them closely, he can clearly see evidence of past hurricanes.
DONNELLY: What happens during the hurricane is that you wash in sediment from the beach, so you’ll have this really mucky dark sediment, and then these light sand layers that are in there that are related to these storm events.
SHEPHERD: Combining the coring data with other environmental information, Donnelly can better understand the historical record of how hurricanes behaved further adding to the ability to predict hurricane behavior today.
DONNELLY: What we can do here is go back in time to other periods that were warmer, colder, had different sorts of conditions and say, okay, what parameters of the climate system are important.
SHEPHERD: Through continued research into path forecasting and digging deep into the historical record, scientists like Evans and Donnelly continue to add to our understanding of hurricane behavior and to provide a first line of defense for one of nature's greatest furies.
A new study by a scientist with the National Oceanic and Atmospheric Administration has found that over the past seven decades, tropical cyclones have slowed down near coastlines around the world.
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