The sun comes up on strengthening Hurricane Dorian on Friday.
GIF: Colorado State University

Hurricane Dorian grazed Puerto Rico as a tropical storm and has since spent the past two days feeding on warm Atlantic waters. That’s allowed the storm to pick up steam with winds over the past 48 hours, increasing from 50 mph to 110 mph as of Friday morning.

The winds will keep build over the weekend as the storm rolls over the Bahamas and are forecast reach 140 mph—which would make Dorian a robust Category 4—as the storm approaches landfall in the U.S. early next week, likely somewhere on the east coast of Florida. That raises huge risks for one of the most densely populated stretches on the Eastern Seaboard on a busy holiday weekend, a kind of Jaws setup but with a monster storm instead of a monster shark.

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“Nobody’s off the hook,” Jamie Rhome, the head of the National Hurricane Center’s (NHC) storm surge team, told Earther. “One is often enticed into this ‘I can wait a little bit longer and the models will shift’ approach. But at this point, the Florida east coast has got to be preparing.”

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In the case of Dorian, preparation means getting ready for multiple impacts that could start well before landfall and last beyond it owing to a few atmospheric quirks that will let Dorian stick around much longer than anyone would want. Right now, the storm is riding what Rhome called “steering currents,” that is winds in the atmosphere and areas of high and low pressure that act as guardrails for the storm. They’re currently ushering it to the northwest at a pretty steady clip of 12 mph according to the latest NHC update. But the steering currents are forecast to break down as Dorian approaches land meaning the storm will slow down. Jason Furtado, a meteorologist at the University of Oklahoma, told Earther in an email that “will leave Dorian ‘stuck’ somewhere near/over Florida under weak steering flow.”

That gives it more time to push storm surge ashore and lash the coast with strong winds and heavy bands of rain. The storm is forecast to make landfall early on Monday morning and then move north over central Florida as a hurricane through at least Wednesday.

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While NHC has yet to start issuing storm surge forecasts because Dorian’s exact track could change, the prospect of a high surge is, well, high. The storm’s wind field—a key factor for piling up water and pushing it ashore—is growing as are wind speeds. A stall off the coast would allow for even more time to drive the storm surge slamming into the coast. Climate change has caused seas to rise by about nine inches in southern Florida, and Dorian will also be arriving on the King Tides, which adds a few extra inches still to any storm surge forecast. But it’s the storm itself that will still most of the heavy lifting.

“I’m not losing sleep over the King Tide, I’m losing sleep over the potential storm surge,” Rhome said.

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All this points to a need for residents up and down Florida’s east coast to prepare now. Rhome, who lives in Broward County, said he’s moving through his hurricane plan by stocking up on food and water to last multiple days and batteries in case of power outages. While a number of NHC forecasters will stay put at the agency’s Miami office to help inform the public, Rhome was adamant people in Florida pay attention to what evacuation zone they’re in and to heed all orders to leave the coast if (or more likely when) evacuation orders come down.

Hurricanes are ranked by wind speed, but storm surge and floodwaters are what kill most people. When evacuation orders come down, that’s generally why they’re being issued.

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“If an evacuation order is given for your community, that means conditions could be potentially life threatening,” Rhome said.

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On top of the increasingly dire forecast, there are also huge concerns because of the number of people in harms way. Stephen Strader, a geographer at Villanova, has noted what he calls the “expanding bullseye effect” of more people living in harms way. The number of homes in Florida has increased twentyfold since 1950, with some of the heaviest development on the east coast and central part of the state. Those areas are exactly where Dorian is forecasted to head. Add in an untold number of people who headed to Florida for the last long weekend of summer and you have the potential for a large number of people who don’t understand hurricane risks or evacuation zones, clogged evacuation routes, and more people in need of assistance once the storm passes.