Watching Florence 

Posted: 10:53 am Sunday, September 9th, 2018

By Kirk Mellish

FLORENCE FORECAST TO RAPIDLY INTENSIFY INTO A MAJOR HURRICANE BY MONDAY.

In case you missed it in a prior post about Gordon, I’ll point out again that too much attention is often paid by the public and the news media to what “Category” a tropical cyclone is 1-5 and the maximum winds associated with it. The category is based on the maximum winds and how low the pressure is near the eye of the storm.

The eye of the storm can be as small as 20-40 miles in diameter. That is a tiny fraction of the storms size, so those winds will impact a tiny fraction of any land area struck by the storm. These storms can be hundreds of miles in size. Much lesser winds, while still dangerous and damaging will impact most areas. Isolated tornadoes also occur.

Almost always the greater danger and loss of life comes not from wind but water: in the form of flooding from torrential rain, waves and storm surge.

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Keep in mind the error average at 5 days:

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Getting better all the time but at 5 days the mean location error was 150 miles last year.

Please keep in mind the “Cone of uncertainty” you see on forecast maps is NOT specific to that storm, but is based on these average errors. The cone is the same all season long.

The cone of uncertainty is NOT based on the models but on the historical 5-year error average of NHC official forecasts. Negative impacts can and often do occur well outside of the cone!

There is still a possibility of some weird stuff with Florence with looping or stalling after it gets near or inland by Friday.

Despite the current trajectory, a path further south can’t be ruled out yet. So Georgia to Northern Virginia still need to be on-guard. 

*IF* Florence stalls inland it will likely cause devastating and maybe even historic flooding somewhere from Maryland southward.

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5-DAY ACCUMULATED RAINFALL ESTIMATE:

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There will inevitably be adjustments to the forecast track and rain amounts, expect changes in the days ahead.

If you’ve been following my blog and twitter posts over the past week you also know we are watching ISAAC:

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Follow me on Twitter @MellishMeterWSB.

 

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