Warming Atlantic ocean could intensify frequency of hurricanes

ORLANDO — There’s good news and bad news on the hurricane front: Water in the Pacific could be shifting to create less-hospitable conditions for the storms to form, but things in the Atlantic seem to be perking up.
Cool water in the Pacific Ocean seems to be warming slightly, though La Niña is expected to linger through the spring. This weather pattern’s disappearance would make it harder for storms to form.
The water in the tropical Atlantic Ocean is also warming, however, and other conditions are in place in the Atlantic to keep water temperatures rising. That’s good for hurricanes.
That’s the assessment of Phil Klotzbach with Colorado State University, speaking at Friday’s closing session of the National Hurricane Conference.
Klotzbach is assuming much of the forecasting work done until now by William Gray, the Colorado State professor who has issued forecasts of hurricane seasons since 1984.
The pair’s next forecast will come Wednesday at a hurricane conference in the Bahamas.
Their last forecast in December called for 13 named storms and seven to become hurricanes. Three of those are expected to grow to storms of Category 3 or larger. That is slightly above the long-term average for a season.
It doesn’t appear that the numbers will go down in the new forecast, said Gray, who also spoke at the conference’s closing session.
“They may stay the same,” he said.
Gray said active seasons are likely to be with us in coming years.
“We have this multi-decadal cycle that’s bringing many more storms to the Atlantic, particularly category 3, 4 and 5 storms,” Gray said.
Hurricane frequency in the Atlantic swings from calm to active over periods that last 20 to 25 years. The Atlantic entered an active phase in 1995.
Much of the swing in activity depends on ocean circulation driven by changes in salinity, Gray said.
While one part of the globe may be drifting into neutral conditions for hurricanes, neither aiding their formation nor hindering them, the opposite side of the world is starting to favor hurricanes.
La Niña, when water in the tropical Pacific cools below normal, is still in place though weakening slightly, according to the Climate Prediction Center.
It may wane by the end of spring. Forecast models are split on whether it will stay through summer.
Klotzbach said spring is a difficult time for forecasters to predict what La Niña will do in the summer.
The cool water of La Niña weakens the jet stream that blows from the west, seven miles above the earth. The weaker jet stream means those winds that normally can inhibit hurricane growth aren’t in place, and it is easier for storms to form.
Even if La Niña weakens and the Pacific returns to neutral conditions, water temperatures in the eastern Atlantic have risen in the past few months, Klotzbach said.
Also, trade winds moving from the east have diminished, and air pressures have dropped.
The three work together. Lower trade winds allow the water to warm faster. Lower trade winds also mean lower pressure, and lower pressure can mean calmer trade winds.
“Traditionally when you see that warming, especially in the eastern Atlantic, you see more hurricane activity,” Klotzbach said.
He said water temperatures in the Atlantic were lower in 2007, one reason many of the storms that formed didn’t become too powerful.