Why is Laura strengthening when Marco weakened?

Tropical Weather Education
More WFLA Tracking the Tropics

MOBILE, Ala. (WKRG) – As tropical systems approach the Gulf Coast, you may hear the First Alert Storm Team mention whether the storm is heading into a favorable environment for strengthening or not. But what do meteorologists look at to determine whether or not a storm will intensify?

As Marco neared the Gulf Coast, it faced a rough environment which weakened it before landfall. On the other hand, Laura has entered the Gulf of Mexico not too far behind Marco, but will encounter the opposite environment.

For a strom to strenghten, the environment needs three main ingredients: warm waters, high moisture, and low wind shear (the change of wind speed or direction with height). Marco had the warm waters and high moisture, but did not have the low wind shear. Laura on the other hand is heading to an environment has all three.

Jason Beaman, National Weather Service Mobile, says, “With Hurricane Marco, what came against it was very strong winds in the upper levels of the atmosphere. And what that basically did was shear all of the thunderstorm activity away from the low-level center.”

A hurricane is basically a heat engine. For it to intensify, it has to have a way to ventilate. With Marco, the winds in the upper levels of the atmosphere where this ventilation occurs, were too strong for this to happen (high wind shear). With Laura, we have light winds moving clockwise in the upper levels and surface winds moving counterclockwise (low wind shear). This helps the engine run smoothly.

Beaman adds, “That allows those thunderstorms to grow around the storm and kind of…serves as an exhaust in the upper levels of the atmosphere. It allows the storms to continue developing, growing and organizing around the center and that is how you get strengthening within a hurricane.”

Because Laura’s environment has warm waters, lots of moisture and low wind shear, we expect it to continue strengthening.


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