Glenn ‘Hurricane’ Schwartz’s Blog: Hurricane Nate Hits Gulf Coast, Rain Heads Our Way

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NBCPhiladelphia.com
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Strengthening and Moving East

nTropical Storms and Hurricanes generally need water temperatures of at least 79 degrees Fahrenheit (26 degrees Celsius) to form and strengthen. The warmer the water is, the more “fuel” is added to development. The waters in the Gulf of Mexico are usually warm enough this time of year. But they have been running above normal (just like the Caribbean). Here is the latest map of water temperatures compared to normal.
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But it’s not just the water temperature at the surface that is important. The depth of the warm water can add even more fuel for development. We measure this in a term called “Ocean Heat Content.” This one shows just how extreme the water conditions are.

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The actual numbers aren’t important here. Just look at that “red” the area in the Gulf of Mexico. If Nate tracks over that warm area, it will be stronger than if it tracked just to the west. That type of red area in the Gulf is similar to where Katrina tracked in 2005, when it strengthened rapidly.

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Nate has already intensified today, even with a pretty chaotic structure. Poor structure plus a fast movement usually limits strengthening. But Nate’s pressure continues to drop as it enters the Gulf-not a good sign.

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So Where Is Nate Going? It's Pretty Clearn

Sometimes, the track of a hurricane is very uncertain. Not this time. When they have a significant “steering current” to guide them, computer models tend to agree on the future movement. That is the case with Nate. Look at some recent “Spaghetti Plots”, showing various model forecasts.

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Not only is there terrific agreement on a track in the general direction just east of New Orleans, but there’s also high confidence in a track that ends up right over our area early next week. That’s the reason for our rain forecasts for Sunday night through Monday night. This time, we need the rain. We’ve gone 17 straight days without measurable rain in Philadelphia! It should be a number of hours of a soaking rain. Since Nate will be moving so fast by the time it gets here, the total amount of rain will be limited (1-2 inches is expected).

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Getty Images

Intensity Forecast: Really Tough This Time

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We were pretty confident that Irma and Maria were going to strengthen rapidly. Yes, the water temperatures were high. But the key factor was the lack of “wind shear”. Hurricanes can be surprisingly fragile, especially in the formation stages. The wind patterns above the developing storm have to be favorable, meaning very little wind shear. It was the lack of shear over Irma and Maria that led to their rapid intensification. And the lack of shear has been a significant feature throughout this hurricane season.nHere is a good explanation of what shear is, and how it affects hurricanes.

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AP Photo/Gerald Herbert

The shear question is added to the question of how much land impacts Nate. It is near the northeast corner of the Yucatan Peninsula tonight. The land is very flat in that area, so it’s not enough to destroy Nate, but it can help delay or limit intensification a bit. It already looks like the Yucatan is affecting the circulation.

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Right now, the National Hurricane Center is predicting Nate to become a Category 1 hurricane by the time it hits the Gulf Coast. But they still mention that rapid strengthening is not out of the question. The fast motion leads to fewer hours over the warm Gulf of Mexico, so we’ll see how much Nate can strengthen before it hits land. It won’t take a strong hurricane to cause big problems in New Orleans, since the pumps still don’t work and flooding comes easy there.

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