Yesterday, I started a series sharing some candid thoughts and observations from NHC Hurricane Specialist Stacy Stewart at last week’s Eastern U.S. Weather Conference.
While hurricane track forecasts have improved, intensity forecasts have not kept up. The average 24 hour intensity error is just 10 knots, and 15 knots at 48 hours. But at 72 hours, the average error is one category on the Saffir Simpson Hurricane Scale. Or as it is called this year, the Saffir Simpson Hurricane Wind Scale. This decoupling of surge from the wind scale is a critical move in preventing poor decisions like people made in Hurricane Ike, thinking a category two storm couldn’t be that bad.
Captain Stewart says that sea surface temperatures in the Main Development Region (MDR) in the Atlantic are currently running 4C above normal. This anomaly will likely be in place all season, although the magnitude will lessen to about 1C by the latter half of the season. This will lead to an early active season and a prolonged, active late season.
He explained how shear is in the principal factor in hurricane formation and intensification, not upper oceanic heat content, like many meteorologists assume. You don’t have to look back very far to see an example of this at work. Last year, the waters of the MDR were warm as well, but we had a below normal hurricane season, because of the shear caused by El Nino. It is like a car. A full gas tank does not specify how fast a car will go. That is governed by the engine. The shear is the gas pedal. Every system that comes off Africa is a cat five wannabe that has to battle dry air, cool waters, interactions with land and shear in order to grow, but shear is the big limiting factor. So we all need to share Capt. Stewart’s mantra: “Go Shear!”
He also said that by late July, we will have a better idea about how the landfall trends will work.
By that time, the Bermuda High will have established its location. While it will move around, its general location will determine steering current trends.
Capt. Stewart said that one of his pet peeves is the media braving the elements of a storm just for ratings. He feels that the media needs to leave before conditions deteriorate, telling its audience that they are leaving before things turn bad.
Finally, he says that Haiti is a big concern, with over one million people living in tents. The country is very vulnerable to the rain and wind of tropical cyclones.
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