We have been talking about Hurricane Earl since Saturday, and we are getting closer to his impact. As of Thursday morning, the trend what we have been talking about with a westerly shift is going to occur. In other words, the center of circulation will be closer to our coastline.

Big question is, why is this happening? This partially has to do with the high-pressure cell that is over the central Atlantic that typically steers tropical systems. However, when you go deeper into the analysis, you need to focus on the upper level features, especially a trough that is to our west. At the moment this trough of low pressure is producing showers and thunderstorms in the Northern Plains. Not only is the movement of this feature important, but rather its orientation.

Winds on the western side of the trough are very strong comparable to its eastern side. This means that the trough will dig, or amplify and move farther south. At the same time, the fast winds as they approach the base of the trough will help to tilt it. This will be a northwest to southeast tilt (AKA negative tilt).

Overall, rather then pushing Earl way out to sea, this orientation will cradle the storm and aid a movement closer to the coastline and increasing the danger for our area. In most cases when a tropical system comes up into northern New England, the west to east winds are so strong that it rips the storm apart and quickly move it out to sea. However, with this “negative tilt” not only will this allow Earl to hug the coast closer, but possibly move northwest, making landfall on the Maine coast.

If you want to take a look at this tilt, click here. This image will show you the evolution of the trough that moves from the Northern Plains to the Great Lakes.

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