Wind shear weakens storms. Hurricane Michael just shrugged it off.

When hurricane expert Phil Klotzbach is forecasting a storm he relies heavily on two factors: water temperature and wind shear.

Warm waters can feed a storm system, causing it to build in strength as it nears land. But a high velocity of wind shear can knock it down by cutting the top off a developing storm, robbing it of the heat that can fuel it.

So when meteorologists saw the amount of wind shear surrounding Tropical Storm Michael this past weekend, they thought it would follow the usual model. The shear should have reduced the intensity of the storm, maybe kept it to a Category 1 or 2 hurricane.

But as all of Florida knows, that's not what happened.

When Hurricane Michael struck the Panhandle on Wednesday it was a fast-moving Category 4 monster and the third most powerful storm by minimum central pressure within the last century.

Michael "didn't seem to care," about wind shear, said Klotzbach, a research scientist in the Department of Atmospheric Science at Colorado State University.

"When it came to this hurricane, it was an overachiever," he said. "It did more than expected given the conditions it was under."

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Michael slammed North Florida with 155 mph winds — just shy of Category 5 strength — sent up to 10 feet of storm surge into coastal areas and damaged and demolished homes and businesses across the Panhandle.

One reason why Michael shrugged off 20 to 25 mph wind shear might be the size of the hurricane, which could have made it too big and unruly to be affected by it. Michael was about 350 miles wide, according to the National Hurricane Center — or almost as wide as the state of New Mexico.

When it first became a hurricane on Monday, the hurricane center sent out an 11 p.m. advisory saying the storm's gain in strength defied the odds.

"Either the shear calculations are unrepresentative or Michael has become more inertially stable due to its large eye and large outer wind field, making it more shear resistant," the report said.

By comparison Tropical Storm Nadine, which is churning west from the coast of Africa, is facing the same level of wind shear that Michael faced, or up to 25 mph. But Nadine is starting to lose strength because it's a much smaller storm that can't resist the calming effect of wind shear.

But size is just one factor affecting shear. Klotzbach said scientists will use Michael to better study the effects of wind shear on tropical storms. Wind shear also failed to slow down Hurricane Florence, which peaked at Category 4 strength last month before it flooded the Carolinas as a Category 1 storm.

He said this hurricane season has left researchers plenty to study in the coming months.

"There will be some good discussions coming out of the next various hurricane conferences," Klotzbach said. "Over the next few months hopefully we can get a better understanding as to what happened."

Contact McKenna Oxenden at moxenden@tampabay.com. Follow @mack_oxenden