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La Niña may bring mild winter to region, forecasters say

A Sept. 10, 2020, satellite image shows tropical

A Sept. 10, 2020, satellite image shows tropical storms forming in the Atlantic Ocean. A La Niña weather pattern often leads to a busier Atlantic hurricane season. Credit: NOAA

Yes, a La Niña weather pattern that may herald more powerful storms now looks more likely, forecasters say.

And yes, a multitude of other more local weather systems either may prevent or intensify any tropical storms and hurricanes.

And yet — the second La Niña winter in a row might please anyone who prefers a mild mid-Atlantic winter.

"It’s not a ‘Take it to the bank,’ but more times than not, in a La Niña winter, there is below normal snowfall, average to slightly milder temperatures," said David Robinson, the New Jersey state climatologist who manages the Rutgers New Jersey Weather Network.

"And precipitation-wise, we still get rain, it’s not like we have a drought or anything like that."

The chances a La Niña will arise during August to October and last through the winter rose to 70%, the National Oceanic and Atmospheric Administration said last Thursday.

The odds were a lower 55% in its July estimate, when it issued a watch, signaling conditions were favorable. And a La Nina was not expected until September to November, also continuing through winter.

La Niña, by dampening the wind shear that can rip hurricanes apart, "is more conducive to storm development," Robinson explained. Wind shear, viewed as a steering current, is a change in speed or direction.

"Once these storms form, they are somewhat dependent on steering currents; sometimes they are a bit like a bowling ball," he said, "and can pound their way through."

In early August, NOAA raised its Atlantic forecast for the June 1 to Nov. 30 hurricane season to 15 to 21 named storms — including the five that already have struck. That was up from 13 to 20 in May.

"However, cautioned Mary Knapp, assistant state climatologist, at Kansas State University’s Weather Data Library in the Department of Agronomy: "It isn’t a La Niña yet; they are just saying the signals are there for it to develop this fall."

"You can have other things that have a great influence, so you may not have what we consider a typical La Niña pattern."

That list of other factors, for example, includes the Bermuda High, the jet stream, and, of course, just how potent a La Niña develops.

The Bermuda high pressure system, with its falling air drying and cooling often hovers over the resort island in summer.

Its clockwise spin, if strong, propels hurricanes toward the Eastern Seaboard and then north, NOAA says. A weaker Bermuda high does not carry storms as close to the coast, and sends them north sooner.

La Niña is one of the systems that exemplify the interplay between the air and oceans. It forms when the equator’s easterly trade winds intensify. That pushes the Pacific Ocean toward Asia, allowing the sea’s coldest layers to rise to the surface off South America's west coast.

The jet stream then veers north, toward the U.S. West Coast, opening the door for more hurricanes, though experts say they tend to head north from the South to the Ohio Valley and the Great Lakes, instead of along the East Coast.

La Niña’s opposite, El Niño, can curb storms, as it drives the jet much further south, into northern Florida and the Gulf of Mexico, according to NOAA.

El Niño arises when easterly trade winds weaken — or even change direction. So less of the ocean’s cooler bottom waters rise to the surface off western South America. And that warmer water can, NOAA says, "slosh" toward the eastern Pacific.

While storms were deprived of the moisture they need, starting in mid-July, thanks to a large plume of dry air and dust blown across the Atlantic from the Sahara Desert, that lull has ended, the experts said.

Remnants of Tropical Storm Fred by Monday morning should reach the stretch of the southern United States from western Louisiana to the Florida panhandle, while Tropical Storm Grace is spurring warnings through much of the Caribbean, from Antigua to the Virgin Islands to Puerto Rico.

Both storms came from the Cape Verde Islands, a few hundred miles off northern Africa’s west coast, where some of the worst storms are born.

Noting the chronological peak of the Atlantic hurricane season is not until Sept. 10, Robinson said: "What these two storms are telling you is that Cape Verde season is open for business, but it isn’t opening with a Big Bang start."

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