OULDER, Colo., Nov. 22 — Snapping like rubber bands pulled too tightly, tangled magnetic fields on the surface of the Sun have been spewing waves of radiation and superheated particles at Earth.

So far, the damage has been relatively minor in comparison with significant communications disruptions three years ago. The culprits this year are three volatile sunspots that began erupting last month and set off blackouts in Sweden, damaged satellites and forced some airlines to divert flights from polar routes to escape extra radiation.

And now, after a three-week lull while the Sun's rotation spun them out of view, the sunspots are back within striking distance. The one with the potential to produce the most fireworks, Region 507, is expected to fix its sights squarely on Earth just as Thanksgiving arrives. While all three have decayed a bit, 507 is still roughly eight times the size of Earth.

Predicting the level of havoc that can be wrought by 507 or any other exploding sunspot is a minute-to-minute science. The erratic nature of exploding sunspots leaves researchers with as little as 30 minutes to warn of radiation storms or as much as 17 hours to prepare for speeding clouds of plasma.

Nowhere perhaps is the pressure greater to assess the magnitude of these blasts than within the walls of the Space Environment Center here, home of what could be called the solar storm trackers. Vivid, up-to-date images of the Sun captured by satellites a million miles from Earth constantly blare across an elevated, oversize television screen demanding the team's attention.

To the forecasters here, every sunspot has its own personality and can be dangerously unruly or quickly fizzle into obscurity.

For the last month, the rotating team of several space weather forecasters at the National Oceanic and Atmospheric Administration has focused on nothing else, darting from computer images of the sun flares to e-mail messages and to telephone calls in an effort to warn thousands of subscribers, like utilities, NASA and the airlines, of the newest storm ratings.

They also answer queries from the public that range from the humorous, like the woman who blamed a speed-trap radar reading of 90 miles an hour on a flare, to the tragic, like those who believe relatives' pacemakers failed during such events. Or those who complain the hair on their arms stands on end. Or that their flaring arthritis is in sync with a solar flare. Or that a homing pigeon loses its internal compass in a geomagnetic storm.

And lately, with the likelihood of storms resuming, so too has the number of calls from concerned travelers fearing extra radiation during their holiday flights.

On Thursday, when the sunspots reappeared with a new round of storms, the space forecasters fell back into formation. A locustlike cloud of charged particles shot out of the Sun at more than two million miles an hour, swarming Earth just after midnight.

Standing beside a fortress of computers, William Murtagh, a forecaster, described the storm as relatively slow moving. Still, he brimmed with the satisfaction of knowing that at least for the day, he had tried to restrain the Sun's devastating fury.

"This one we predicted would arrive in 50 hours, and it actually reached us in 46 — so I'd say that's a pretty good job," Mr. Murtagh said with a smile. "We expected major to severe geomagnetic storm levels, and that's exactly what we're getting now — right on target."

Those predictions have far-reaching impact. The agency's subscribers also include the Coast Guard, most airlines and the military.

The storm trackers' alerts prompted power companies throughout North America to switch to "safe mode" to protect grids from collapse with the heightened solar storm currents. All it took to plunge six million people in Quebec into darkness during a storm in March 1989, Mr. Murtagh said, was one transformer that overheated and shut down.