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How do meteorologists determine the forecast cone for storms like Hurricane Florence?

The updates will come like a drumbeat every six hours this week. Where is Hurricane Florence, where is it going, and how strong will it be?

The National Hurricane Center processes countless data points and dozens of supercomputer forecast models to answer those questions.

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The cone represents the most likely track center forecasters expect the storm to take, based on a suite of forecasting models, each with its own strengths and tendencies toward errors. Meteorologists often refer to a collection of these forecasts as “spaghetti models” — named because they often resemble a batch of noodles that are sometimes mostly oriented in the same direction, but other times a tangled mess.

To develop the forecast cone, they analyze the various model predictions to determine the most likely path. The more those models agree, the more confidence meteorologists have — and the narrower the cone can be.

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Hurricane Florence is forecast to hit the Southeast coast as a major storm later this week. What could it bring to Maryland? Strong winds, heavy rain and flooding and/or storm surge, depending on its track.

The models are run regularly with the latest statistics on a tropical cyclone’s location, wind speeds and surrounding atmospheric conditions. And the Miami-based hurricane center analyzes that information constantly, to release new forecast cones at least four times a day — in Eastern time, at 5 o’clock and 11 o’clock, every morning and night.

Once coastal hurricane watches are warnings are posted, the updated forecasts come every three hours, morning and night at 2 o’clock and 8 o’clock, too.

The width of the cone is set to include two-thirds of the historical errors in hurricane forecasts over the past five years. That means it’s designed to include the path meteorologists think is most likely, but also account for the chance that they are slightly off in their predictions.

They throw out the widest errors, because otherwise the cone would be too wide to be useful. But that doesn’t mean storms always follow the cone.

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“Based on forecasts over the previous 5 years, the entire track of the tropical cyclone can be expected to remain within the cone roughly 60-70% of the time,” the hurricane center notes on its website.

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