As the full moon rises, backlighting the horizon, the water transforms the moonlight into a golden mosaic. The surface responds to a gentle breeze, generating ripples that scatter the light, reunite it, scatter it again.

It is another hauntingly magnificent twilight off the North Carolina coast - a scene Paul Kocin hopes never to witness in person.

The setting is the western edge of the Gulf Stream, and Kocin, who has spent his career studying storms, knows that this region is an atmospheric minefield. This is where the mighty stream and its ever-flowing warm current conspire with the atmosphere to set off some of the most dramatic fireworks on Earth.

"It's an extremely dangerous, mystifying area that has a profound effect on weather," says Kocin, who deconstructed the Gulf Stream-incited "white hurricane" of 1888, among the most famous winter storms in history. "I try to stay away from it as much as possible."

The stream is a celebrated storm-maker, for much the same reason that it has become a focal point of global-warming research: It is a prodigious mover of heat. Only in the last generation have scientists come to appreciate its power, and it continues to surprise them.

They now know that the Gulf Stream has been an agent provocateur in almost every important winter storm to hit what is today the Interstate 95 corridor. Among them: the historic blizzard of 1888, the 1962 Ash Wednesday storm that cut Long Beach Island into five pieces, and the record 30.7-inch snowfall in January 1996.

Even in this enchanting setting off the North Carolina coast, the Gulf Stream leaves a trail of evidence that hints at its dangerous side. The languid air borne on the current is distinctly tropical and swollen with water vapor. The vapor is palpable to the skin - as Benjamin Franklin observed when he encountered the stream in 1726. It condenses on the cool, white deck railings of the research ship Nancy Foster. The Gulf Stream is a prodigious supplier of water vapor, the combustible ingredient that has helped fuel the monster storms.

Ordinarily, the mighty stream acts something like the fluid in an immense heating system. Its constantly flowing waters export warmth from the sun-saturated tropics toward the solar-deprived Arctic to steady the planet's temperature.

But occasionally, the stream turns impatient and fast-forwards the process. At least a few times every winter, it mutates into a power source for coastal storms. Those are the great air mixers that rearrange the atmosphere, yanking polar air dramatically southward and shooting tropical air northward.

When the Gulf Stream is overrun with cold air sliding off the continent, it throws its water vapor skyward, where the vapor condenses and returns as rain and snow. The condensation releases massive amounts of heat to further incite the wildly spinning winds that rip sand off beaches and pile snow into head-high drifts. The stream can turn weak storms into strong ones, strong ones into monsters.

"That's why they like us out here," says Jamie Velarque, captain of the Nancy Foster. From the picture windows on the bridge, on this particular night, he is watching the weather closely, listening to the weather radio, monitoring the instruments sending back readings from the surface and from 100 feet under water.

The Nancy Foster is part of the National Oceanic and Atmospheric Administration's navy that ferries scientists on research cruises. But it has another important mission: to send back live data from the stream, where "ground truth" observations are sparse. On this particular day, for example, when satellite readings indicate a water temperature in the upper 70s, the Nancy Foster is showing 84 degrees all the way down to 300 feet.

Early evidence suggests that the Gulf Stream could be a major player this winter. Its waters have been extraordinarily warm and close to the coast. In the view of Len Pietrafesa, a storm specialist at North Carolina State University, it is primed for mischief. During the fall, water temperatures were in the 80s - readings "we have not seen in the historic record," he says. Last week, they were still in the upper 70s off Cape Hatteras. "I expect it to be a wet winter in the Northeast," he said.

His is only informed speculation, for the mighty stream remains a mysterious force. Meteorologists know that the Gulf Stream is a big reason why the mid-Atlantic and Northeast have some of the wildest and most varied weather on the planet. The Atlantic Ocean is an awesome storm factory, and the Gulf Stream speeds up production.

"It's pretty fantastic in terms of its influence," Pietrafesa says. And researchers believe the stream is as vital to climate as it is to weather. Says Pietrafesa: "The system is all linked." Now, with scientists reporting significant changes in the North Atlantic, they have a new urgency to figure out exactly how all the pieces fit together.

Just when scientists think they have found answers, however, the stream comes back at them like a rogue wave flipping a boat.

A perfect storm

On March 9, 1888, residents of the nation's densest population center took little note of a storm approaching the South Carolina coast.

It was expected to affect the Washington-to-New-York corridor during the next 48 hours, but not dramatically. The U.S. Weather Bureau issued prosaic forecasts calling for some clouds and rain.

The weather agency, which by then was taking observations and issuing daily national forecasts, was part of a dizzying era of progress. The gasoline-powered automobile, the streetcar, the dishwasher, the ballpoint pen - anything seemed possible.

As one scientist noted: "Great disasters can be anticipated and obviated."

Nature took exception in 1888.

Shortly before midnight on March 11, the forecast rain changed to snow in Philadelphia.

The winds became so strong that the 10 inches of snow that fell were whipped into 10-foot drifts. The temperature plummeted from the mid-40s to 15, with stinging winds driving wind chills well below zero. Ships were stranded as howling winds blew out tide water from the Delaware River.