Storm Season - Jet Stream

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Blame jet streams for nor’easter blitz

Winter gales. Their driving rains lash New England’s coast, and their snowy blasts pile its waters into gray, spume-topped mountains. These storms, or nor’easters, menace the unwary boater, challenge the meteorologist and keep the Coast Guard watchstander vigilant.

The fall of 2006 was particularly stormy in the mid- and north Atlantic, says George Caras, operations director for

Read the other stories in this package: Storm Season Storm Season - 50-Knot gusts

Commander’s Weather, a Nashua, N.H., forecasting service that routes yachts across oceans and delivers weather data to them at sea. “It has been a very active fall storm season all the way across the Atlantic,” he says.

Caras and his staff have been busy guiding yachts around these storms. November used to be late for delivering a yacht south from New England because of the threat of these storms along the way. But Caras says many owners are leaving later anyway, either to prolong their northern cruising or because their insurance requires them to stay well north during the June 1 to Nov. 30 hurricane season.

With a late start south, these people may be avoiding hurricanes, but they face a bigger threat of winter storms. “You give up one for the other,” says Caras. “Some of these lows get pretty intense.” Squalls off North Carolina’s Outer Banks, in particular, can throw wind out of the northeast against Gulf Stream currents from the south, piling up tall, steep waves.

These storms are nothing to fool with. “They keep us busy,” he says.

Caras attributes the blitz of storms this fall to the convergence of two jet streams: the polar jet stream, which brings cold air down out of Canada and the Arctic, and the subtropical jet stream, which sucks up warm, moist air from the Pacific and Gulf of Mexico. The polar jet stream usually hangs out over Canada and the northern United States, the subtropical jet stream over the Gulf of Mexico and lower United States. The two streams have been merging, bringing together masses of warm and cold air over the middle and eastern parts of the country. That, says Caras, is a sure formula for stormy weather.

The warm air rises as the cooler air sinks, creating low pressure and a counterclockwise circulation that can strengthen and develop into a nasty storm. The system tracks east to the Atlantic, either continuing across the ocean or sidling up the coast to New England, where the circulation kicks up big winds from the northeast, hence the name nor’easter. The winds are out of the northeast, but the storms themselves usually come from the west or southwest.

That’s where the Oct. 28 and 29 storm that rocked New England with 50-knot winds came from. It started as a low-pressure system over Arkansas, where warm air from the South met cool air from the North, Caras says. A very strong jet stream fueled the storm at its upper levels, sucking the rising air up faster and faster and accelerating its circulation. The jet stream, shooting great masses of air down in a loop from the Northwest to the South Central United States and back up to the Northeast, guided the storm along a northeasterly track to Chesapeake Bay, then up the East Coast. It was a fairly typical nor’easter.

Caras says a storm can be especially destructive if it breaks off from the jet stream and sits for a few days. It won’t go away until finally it blows itself out without the energy of the jet stream to fuel it. Another permutation on the winter storm is the weak tropical low that works it way up into the northern latitudes, where it meets cold air and strengthens. Caras says this was the genesis of the so-called Perfect Storm — the one immortalized Sebastian Junger’s 1997 book of the same name, which chronicles the loss of the Andrea Gail with all hands.

The 1991 Halloween storm started as a meeting of cold air from Canada with a weak warm-air low from south over the northeast coast. The low intensified when cold air met warm air and was further fueled by warm, moist air from the remnants of Hurricane Grace. The storm stalled out, whipping up 75-mph winds and waves over 90 feet.

Caras says a nor’easter usually is predictable, but with so many storms in the Atlantic at the same time, this has been a challenging year. The challenge, he says, is finding just the right window so a yacht can steer clear of the storms along its route and still get where the skipper wants to go.

“There’s just been a lot of juicy air coming up from the southern latitudes meeting lots of cooler air coming down from latitudes to the north,” he says. That’s the perfect cauldron for conjuring up winter gales.