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Dave Epstein

Hurricane Dorian: What the latest forecast says

Workers covered stained glass windows with plywood sections at the Santa Maria del Mar Catholic Church in preparation for Hurricane Dorian on Friday in Flagler Beach, Fla. John Raoux/Associated Press/Associated Press

Dorian intensified into a Category 3 hurricane Friday afternoon, meaning it qualifies as a “major” hurricane. That term is reserved for hurricanes that reach Categories 3, 4, or 5. The average date at which the first major hurricane occurs in the Atlantic is Sept. 3, so this is pretty much on schedule for an Atlantic hurricane season.

Expect fluctuations in the predicted track of Dorian this weekend.NOAA/NHC

Potential energy

Ocean water contains a lot of potential energy because of its warm temperature. As the storm approaches the coastline this weekend, it will cross over an area of very warm water with lots of latent heat. This might act as additional fuel for the storm, and it won’t be surprising if it continues to intensify until the point of landfall.

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One thing to watch this upcoming weekend: There will be eyewall replacement cycles when the storm may actually weaken temporarily before regaining strength. This is very typical of large hurricanes.

Potential energy for hurricane Dorian is very high off the coast of Florida.NOAA

Time to prepare

If you are reading this from Florida or have interests in Florida, the best thing you can do is prepare for the impact of this hurricane later this weekend and early next week. Make sure any of your valuables that could be affected by water are safely put away. It’s probably a good idea to check with your insurance company to know what the limits of your policy are. This is the type of storm where people should heed evacuations.

Storm surge

Hurricanes have several components to them. There’s the wind, the waves, and the water, which comes from freshwater rains and saltwater storm surge.

Where this hurricane comes ashore early next week will determine just how bad the storm surge is. If the storm did reach Category 4 status and came ashore north of Palm Beach County, the storm surge south of the eye would not be as major because the winds would be blowing water out to sea, not inland.

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Palm Beach could sustain significant flooding from a hurricane coming ashore to the south of the island. Blue represents about 3 feet of water from a Category 4 storm.NOAA

Storm surges have a much greater effect along the Northern Florida coast than they do on other parts. You can see from the map below that a Category 4 brings up to 9 feet of water on the northern part of the Eastern Florida as opposed to less than that south. The west coast of Florida is more vulnerable to a bigger storm surge.

The steering currents that will force Dorian toward Florida will continue to weaken over the coming days, and this means the storm’s motion will be very slow. There will be a swath of incredibly heavy rain — 10 to 20 inches of it in the path of the storm.

The ultimate location of the heaviest rain will be critical in determining who receives the worst inland flooding.WeatherBell

Freshwater flooding

If Dorian stays further east, the heaviest rain could remain over the ocean. But if the storm were to move a little further toward the left, then that heavy rain ends up over the peninsula of Florida and we are looking at some catastrophic flooding. The potential for a freshwater disaster is, in my opinion, equal or greater than some of the other elements of the storm.

Inland flooding can be worse than a coastal storm surge in certain scenarios.NOAA

New information is constantly being absorbed by forecasters at the National Hurricane Center and by local forecasters. There will be subtle changes in the forecast track and the intensity of the storm throughout the weekend. Some models are probably going to show more significant effects than others, but all models are bringing the potential for a historic event.

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If you are following the storm, there are going to be a lot of possible scenarios. Not all of them will come to fruition, but people should prepare for the reasonable ones.


Follow Dave Epstein on Twitter @growingwisdom.