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Flooding could be Ian’s biggest hazard for inland communities

The nearly Category 5 storm will drop more than a foot of rain over Central Florida, which has already seen a lot of rainfall in recent weeks

The Category 4 hurricane made landfall in southwest Florida on Sept. 28 with 150 mph winds and threats of up to an 18-foot storm surge in some coastal areas. (Video: The Washington Post)

Packing 155 mph winds, Hurricane Ian is expected to bring serious damage to the coastline of Southwest Florida on Wednesday. As the storm moves away from the shore, it could cause an additional life-threatening hazard: inland flooding.

Federal Emergency Management Agency Administrator Deanne Criswell and National Weather Service Director Ken Graham said Wednesday that flooding is among their top safety concerns. Historically, water has accounted for the vast majority of all deaths during tropical cyclones that have made landfall in the United States: 83 percent of fatalities during storms from 2016 to 2018 were water-related, according to the National Oceanic and Atmospheric Administration. Most were from inland flooding; only 4 percent were from storm surge, the agency said.

The National Weather Service predicted Ian would drop more than a foot of rain in areas. Forecasts show the eye of the hurricane looming just south of Tampa Bay, but the entire Florida peninsula could see excessive rainfall. As of 2 p.m. Wednesday, the Category 4 storm was moving forward at a relatively slow pace of 9 miles per hour, which could lead to greater rainfall totals.

Hurricane Ian nearly Category 5 as it nears Florida; DeSantis warns of ‘nasty’ day

As hurricanes move over land, they usually weaken and lose wind strength, but they can continue to bring torrents of rain, which funnel into streams, rivers and lakes, causing serious flooding.

“Even though a lot of emphasis is on the winds and along the coast, one of the problems with hurricanes is the inland flood threat,” said Jeff Dobur, a senior hydrologic forecaster at the National Weather Service. “It’s far away from the center of attention, even though it’s one of the more serious dangers of a tropical system.”

Dobur said Florida is at even greater risk for flooding right now because its grounds are already saturated. A cold front stalled across Central Florida has been dropping rain for several weeks in the area, soaking soils and elevating many river levels near or above normal. As Ian approaches the region, the storm will meet up with the lingering front to drop even more rain.

Where will Hurricane Ian hit? Here’s the outlook for 6 Florida cities.

Ian is expected to bring “a fairly extraordinary amount of rain on top of already wet ground,” said Dobur. “The combination of those two could cause an extreme event as we go into the latter half of this week, into the weekend.”

Florida’s relatively flat and low-lying terrain also lends itself to flooding from overflowing small creeks and lakes, inundating nearby homes and businesses. Because the land is so flat, Dobur said, much of the rain will pond across roads, streets and other urban areas.

Low-lying and flood-prone, Tampa Bay area braces for first major storm in a century

Additionally, urban areas are at a higher risk for flash floods because of concrete surfaces that lead to excess runoff. As cities continue to expand, the threat of flooding increases.

“The nature of flash flooding can really catch people off guard,” said Daniel Hawblitzel, meteorologist in charge at the Twin Cities National Weather Service office in Minnesota. “Flash flooding by nature can have a rapid onset and can inundate areas that typically do not see flooding and sometimes have never seen much flooding at all.”

While hurricanes are categorized by the ferocity of their winds, flooding often poses the greater impact, even far away from where the storms make landfall. For instance, more than half of the deaths associated with Hurricane Ida in August 2021 occurred from drowning and flash flooding as its remnants dropped heavy rainfall in the Northeast — more than 1,000 miles away from where the storm initially made landfall. In 2018, Hurricane Florence brought devastating freshwater flooding through coastal Carolina, resulting in nearly two dozen deaths.

“You hide from wind and you run from water; I don’t think we’ve learned that enough,” said Richard Olson, the director of the Extreme Events Institute at Florida International University in Miami. “The coasts of Florida, and basically anywhere that gets hurricanes, have to be focused on the water component of hurricanes.”

Hurricane hazards are expected to increase as global temperatures rise from human-caused climate change. A warmer atmosphere can “hold” more water — about 4 percent more water for each degree Fahrenheit of warming — which can lead to more intense deluges. Warmer sea surface temperatures also provide more fuel for hurricanes, which allow them to grow bigger, intensify more and drop more rain.

What is storm surge and what causes it during hurricanes?

Previous research has investigated exactly how much climate change has increased hurricane rainfall. For instance, Hurricane Harvey in 2017 dropped up to 60 inches of rain in Southeast Texas, a prolific amount that was made more likely to occur because of climate change. During the historically active 2020 hurricane season, climate change increased hourly rainfall rates from tropical storms by 10 percent.

The Weather Service is currently working to improve forecast flood inundation maps to better inform government officials and members of the public of flooding threats. The maps are generated from a computer that takes into account soil moisture, recent rainfall and forecast rainfall. Dobur said the maps will not only show how high a river will get but also the extent of the potential flood area along rivers. While the maps are available for limited regions, he said the Weather Service is planning a large-scale rollout of the maps for locations across the country in upcoming years.

Even with better forecast maps, however, researchers say communication of the threats may still be an issue.

“People still don’t know what the warnings mean, and that’s a problem, too,” said Jase Bernhardt, a professor at Hofstra University. Bernhardt currently has a paper under review investigating why people don’t take flash flood warnings seriously. The National Hurricane Center is also running several social science projects exploring how to better communicate forecasts with the public.

“Communication is still a huge obstacle, and unfortunately if the communication isn’t good, or if people misunderstand the forecast, then even if the forecast is perfect, there’s still going to be a lot of deaths and injuries,” said Bernhardt.

The Atlantic hurricane season

The latest: The 2022 season started out slow, but has rapidly intensified this fall with conditions prime for storms. Fiona brought severe flooding to Puerto Rico before making landfall in Canada, and now we’re tracking Hurricane Ian as it heads for Florida. For the seventh year in a row, hurricane officials expect an above-average season of hurricane activity.

Tips for preparing: We rounded up seven safety tips to help you get ready for hurricanes. Here’s some other guidance about keeping your phone charged and useful in dangerous weather, and what to know about flood insurance.

Understanding climate change: It’s not just you — hurricanes and tropical storms have hit the U.S. more frequently in recent years. And last summer alone, nearly 1 in 3 Americans experienced a weather disaster. Read more about how climate change is fueling severe weather events.

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