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What Hurricanes and Nor’easters Have in Common

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Vol. III, No. 55

Westport firefighters walk down a flooded Grove Point Road during Hurricane Irene in 2011. Photo by John Kantor.

Westport firefighters walk down a flooded Grove Point Road during Hurricane Irene in 2011. Photo by John Kantor.

Hurricanes and nor’easters are perhaps the two greatest weather menaces for those of us who dwell in the northeast. For those of us who live at the water’s edge, they also bring coastal flooding. Interestingly, both are fueled largely by the same major ocean current just off the East Coast – the Gulf Stream.

Hurricanes need warm water to develop, grow and survive. They are warm core events. Hurricanes, such

Hurricane Mitch 98

This image of Hurricane Mitch from 1998 shows the trademark shape of a hurricane.

as Sandy which visited in October, 2012, are born in warm tropical waters of at least 80 degrees. They need that warmth to sustain their intensity. The sea surface temperature is too cold anywhere around here for a hurricane to form. We never see 80-degree coastal water in the northeast. Even in mid-summer, Long Island Sound’s temperature never exceeds the mid-70’s.

Hurricanes which reach the northeast survive and keep their strength by hitching a ride from the tropics offshore, on the Gulf Stream. The Gulf Stream is a major oceanic current which flows steadily northward along the eastern continental shelf. It is plenty warm enough to stoke the needs of a warm-core cyclone such as a hurricane, even well after we experience the chilly first frost of October. Hurricane season doesn’t traditionally end until November 30th.

Nor’easters, on the other hand, typically start off as a cold front coming off the continent from the west.

There is nothing tropical about them. If it weren’t for the Gulf Stream’s warm water fuel, most lows wouldn’t be worth discussing. When the low pressure center driving a cold front reaches the warm Gulf Stream off the east coast it can intensify rapidly into a serious storm. Such a storm can charge up the coast to us almost any time of year – but the worst storms are in winter. Winter is when the temperature contrasts are greatest. Nasty weather occurs along the boundary wherever there is a sharp contrast between temperature and/or pressure. The greater the contrast, the greater the clash.

A hot bed for such clashes is the Carolinas. There, the undersea continental shelf is not wide, so the Gulf Stream brushes the Atlantic coast not far offshore. Where a cold air mass associated with a low pressure center meets up with the contrasting warm ocean current of the Gulf Stream, things get a little crazy. What we locals call a nor’easter typically starts off as a garden variety low pressure center in the Carolinas. No big deal until it gets jacked up on steroids by the Gulf Stream – the birth of nor’easter.

Still, a storm in the Carolinas is not necessarily a threat to us in the northeast. It takes the Jet Stream to deliver it. The Jet Stream is an upper atmosphere current of air, generally traveling west to east. It carries weather systems along with it. But the Jet Stream doesn’t just stay put. It routinely meanders like a river.

When it meanders northward from the Carolinas to the northeast, we get whatever weather was down there the day before. If it happens to have been a cold front, we all too often get a nor’easter.

As too many of us have learned, when the Jet Stream and the Gulf Stream team up and cooperate like this, the result can be a meteorological wrecking ball.

-JK

Categories: WaterViews

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