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How active hurricane season might be good news for US coast

More but weaker storms forecast close to the coast

3rd warmest water temperatures on record in central Atlantic spotlight how Maria and Jose took advantage of favorable conditions in 2017.
3rd warmest water temperatures on record in central Atlantic spotlight how Maria and Jose took advantage of favorable conditions in 2017.

PONTE VEDRA BEACH, Fla. – It sure sounds counterintuitive: Hurricane landfall around Jacksonville is less likely when a season gets a flurry of storms in the central Atlantic. 

It turns out that weather conditions causing the boost also make conditions unfavorable when storms approach the U.S. east coast. 

It sounds contrary but coastal risk increases in periods generally considered unfavorable for hurricane formation. 

Scientists like Jim Kossin at NOAA are looking at past decades of hurricane activity and the patterns of variability are striking.

Hurricanes are two to three times more likely to rapidly intensify along the east coast during seasons with few storms. 

Even when the overall weather conditions suppress the abundance of storms, the hurricanes that manage to overcome the hurdles are 3 to 6 times more likely to intensify into major approaching hurricanes. 

At the AMS Conference on Hurricanes and tropical Meteorology in Ponte Vedra Beach, Dr. Kossin showed a map with a bullseye of shear parked over Jacksonville and the Georgia coast.

A. Shows red bullseye of shear near Florida when favoriable low shear (blue color) covers the main hurricane formation zone(rectangle box). B. Light red is cooler water off the coast of Florida.
A. Shows red bullseye of shear near Florida when favoriable low shear (blue color) covers the main hurricane formation zone(rectangle box). B. Light red is cooler water off the coast of Florida.

That shear is a good thing when it’s close to home. 

Winds blowing from different directions above a hurricane, called shear, weakens storms.  
 
When sea temps are unusually warm across the main development areas of the Atlantic, shear increases in the southeast United States.

This becomes a hostile environmental barrier as hurricanes approach the US coast even though basin-wide activity is elevated.

Ocean temperature shows a clear trend over the decades in regulating hurricane activity in the Atlantic. Cooler than average water temperatures suppressed activity in the late 1960s to the mid 1990s, while warmer seas had the opposite effect increasing storms between the 1940s through 1960, and again from the mid 1990s to now.

The future expectation for fewer cooler periods will resulting in more numerous storms. While the stronger hurricanes along the coast may be reserved for less active seasons.


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