As a week of winter storms stoked swells overhead Thursday, Isla Vista surfers braved the cold, chop and runoff hazard for a chance to catch some of the area’s biggest waves of the year.

The Scripps Institution of Oceanography in San Diego published swell models showing 20-foot surf at Point Conception and at several points off the Southern California Coast throughout the day, and 9- to 12-foot swells in Ventura and Santa Barbara. The National Weather Service expected the storm to last until Friday evening. Its forecast called for an 80 percent chance of precipitation Friday morning in Santa Barbara, which should taper off during the day.

Although a strong current in the Devereux point break at Coal Oil Point made paddling difficult, a handful of surfers patrolled the waters yesterday.

“It was fun. It was pretty choppy, but pretty big,” said junior geography major Jared Kearns. “It was overhead. The current’s pretty strong; you get caught inside a bunch.”

The bigger waves are a contrast to the usual pattern in Santa Barbara, which typically receives smaller surf from its geographical position behind the Channel Islands.

Most waves are formed by wind, far off the coast. “When you have a storm, any disturbances on the surface of the ocean are going to extract energy from the wind and cause the waves to grow,” said mechanical and environmental engineering Professor Stephen McLean, who works in the Ocean Engineering Lab.

Once waves are formed by a storm, they propagate and move off in all directions. The waves with the greatest energy move in the direction the wind was blowing. As the waves near the shore, the bottom starts to shorten and slow them down, forcing more energy into a smaller wave. The energy, McLean said, increases the height of the waves.

In the summer, most of the swells come from the south and Antarctica. “In our summertime, it’s not unusual for big storms around Antarctica to kick up some large swell,” McLean said.

Most of this swell never makes it to the Santa Barbara Coast because the Channel Islands lie directly between the source of the waves and the coast.

Winter waves, which come from the Gulf of Alaska, are not as blocked by the islands, but are small, nonetheless, because the waves are refracted off the islands. Each direction change decreases their energy.

The storms that passed through Santa Barbara this week drove up swells from the southeast, making the waves unpredictable and turning the ocean into a froth. For better surfing conditions in Santa Barbara, a northern winter storm would need to extend far to the south, like the El Ni-o storms that raised heavy surf in 1998.

“When we had El Ni-o, the storm was pushed far further south. The result was we got a lot more weather, a lot more wave action,” said mechanical engineering graduate student Tim Maddux, who frequently surfs at Rincon Point near Carpinteria. At the height of El Ni-o in January of 1998, Rincon received unprecedented 20-foot waves. “The downside is you get all the wind and rain and runoff associated with that. It’s kind of a double bind.”

Maddux cautioned against the dangers of storm surfing, including the currents that trapped two UCSB students earlier in the week near Campus Point. A strong current at Coal Oil Point and the Devereux surf break rapidly pushes surfers down the beach toward Campus Point.

“People need to be careful. When it gets big at Devereux, you just get washed down to I.V.,” Maddux said. “What you need to do is not only know how to get into the water, but where you need to make an exit.”