Florence has spent several days as a powerful category 4 monster, nearly reaching category 5 status earlier this week for a short period of time. Since then, under-modeled shear and dry air have caused Florence to weaken a bit, going from winds around 140 mph to winds of 110 mph, now making it a category 2 hurricane. This has unfortunately sent a confusing message to the public, bringing forth the idea that this weakening will mean lower impacts for the Carolinas and southeast coastline. We want to stress that this will not be the case. The fact that winds have lowered by 30 mph will not make this storm non-catastrophic, and also begs a bigger question about the Saffir-Simpson scale and whether it does more harm than good when categorizing hurricanes by strength.

The Saffir-Simpson scale only takes in one aspect of a hurricane: the wind. The problem with this is that wind is actually the least deadliest aspect of a hurricane in most cases. Rainfall and storm surge cause more death and destruction than wind in nearly every single hurricane. Even with this being the case, hearing that a hurricane has weakened from a category 4 to a category 2 makes the public feel as though it is a lesser threat. But that’s not reality.




Wind Speeds Lower, But Wind Field Expands: 

Yes, the maximum wind speeds have come down with Florence (now 105 mph), but the overall wind shield has expanded greatly, meaning more areas will be impacted by wind issues. The inner core is not as tight due to some dry air and wind shear, but the outer core of the storm is actually getting ventilated by these inhibiting factors, allowing tropical storm and hurricane force winds to extend out hundreds of miles.

You can see our max wind gust forecast posted below:

No Change to Storm Surge and Rainfall:

As we stated before, while winds have come down a bit, there is NO change to the storm surge and rainfall forecasts. If anything, these aspects of the storm have increased in severity. We’re still talking about widespread 20-30+ inch rainfall amounts along with water rising from storm surge over 10 feet at some locations.

This will cause major issues for all coastal areas, as well as areas further inland. The immediate coastline of SE NC will likely see extreme flooding from a combination of 20+ inches of rain and surge 10+ feet. Structures and houses will be completely under water in some spots, with catastrophic damage. Add in the wind gusts to 100+ and you’re talking about a potentially disastrous scenario.




Surge and flooding from rainfall are the deadliest aspects of hurricanes, and we expect it to be no different with this one. Below is our latest forecast for both rain and storm surge, which remains mostly unchanged from yesterday:

The Most Overlooked Threat: Interior Flooding:

As with any hurricane, the focus is usually on the coast. And this makes sense, because by nature hurricanes come from the ocean, make landfall, and then weaken once inland. But what history tells us, and especially this time around, is that a storm that stalls and slowly moves inland can bring unmitigated and unexpected disaster to inland areas.

Model guidance is very insistent on spreading 6-10 inches of rainfall into parts of interior North Carolina, South Carolina, Georgia, and even Tennessee. Parts of West Virginia and Virginia will also see some effects. With near record-breaking rainfall so far this summer for parts of the Mid-Atlantic, a combination of 6-10 inches of rain and tropical storm or even hurricane force winds is a disaster waiting to happen further inland. The southern spine of the Appalachians, which will be under the gun with Florence rainfall, just cannot handle that much water right now. Rivers, creeks, streams, along with low-lying and flood prone areas, are likely to go under water later over the weekend and into early next week. This may cause huge issues that many are not anticipating. It’s important we keep an eye on this.

Above is the latest from the National Weather Service, forecasting high rainfall totals all the way back inland towards the Appalachians and eventually Mid-Atlantic and Northeast.

Check back in this evening for a special WeatherOptics video breakdown as the first rounds of Florence really begin coming ashore.



Author

Currently leads business development and forecasting across all sectors and is the Founder and CEO. Pecoriello founded WeatherOptics in 2010 as a blog called, Wild About Weather, which quickly gained a following. He also launched an app in 2013 called, Know Snow, designed to accurately forecast the chances of school closings.

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