Ocean Motion

Wind and water--two of nature’s most elemental forces--combine to produce one of Orange County’s best-known attractions, the waves that reach its beaches. Three recent storms in widely separated locations have helped end a summer-long run of flat surf. Here’s how, whence and why swells reach the beaches of Orange County.

Storms That Send Us Swells

Storms driving waves to Orange County beaches normally take place at three distant points. Wind-driven swells travel thousands of miles in some cases, depositing waves on local beaches. Here’s where waves are wrought:

A. Northern Hemisphere Storms

They typically develop in the northeast Pacific, more than 2,000 miles away. The fetch--the area across which the wind blows to build a swell--can be 1,000 miles in diameter, with winds in excess of 75 m.p.h. Intervals vary because storms are relatively close and swells mix.

B. Tropical (Mexican) Storms

They need warm water to gain strength, typically forming roughly 1,500 miles from Orange County, off mainland Mexico, with up to a 300-mile-diameter fetch. When they drift northwest into cooler waters off Baja and Southern California, they lose some wave-making potential. Wind speeds are higher--they can reach 150 m.p.h.--but they are smaller in size.

C. Southern Hemisphere Storms

They travel the greatest distance to Orange County--some more than 7,000 miles, taking up to two weeks. They form as far away as the Antarctic ice pack, south of New Zealand. The point-of-origin fetch can be more than 1,000 miles in diameter, with wind speeds exceeding 75 m.p.h.

Sheltered From the Storms

The Southern California coastline is partially sheltered by a series of natural breakwaters, so we don’t feel the full force of remotely generated swells. Point Conception, offshore islands and shallow banks off the islands all contribute to reducing swell size. Orange County is exposed to only a narrow range of northern Pacific swell but subject to a wide range beginning in the South Pacific and near Mexico.

Northern Hemisphere

Swells generated by storms in the northern Pacific are cut off by Point Conception and the Channel Islands. They reach Orange County via a window between the Channel Islands and Santa Catalina Island. An early season storm near the Aleutian Islands, a remnant of Typhoon Oscar, has brought recent high surf to North County and Huntington Beach.

Southern Hemisphere

Swells travel from the far South Pacific but are blocked by Santa Catalina and San Clemente islands. The approach to the county uses an avenue that skirts the east side of San Clemente Island. South County beaches recently were hit by 3- to 5-foot waves, the product of a storm off New Zealand more than two weeks ago.

Tropical (Mexican) Storms

These swells use the same approach as those from the Southern Hemisphere, but travel closer to shore. The path is parallel to the coast and passes San Clemente before normally reaching land around Newport Beach and Huntington Beach. Hurricane Juliette, off Baja, is the genesis of 4- to 6-foot surf at Huntington and Newport beaches.

** O.C. Surf Outlook

And there’s more on the way...today’s surf forecast for county beaches is 4 to 5 feet, swell direction is southwest. Hurricane Juliette has curved to the northeast and will send solid overhead surf to most local beaches through Monday. New southwest and northwest swells, filling in through Tuesday, should bring more good conditions.

Whipping Up the Water

The waves we see breaking on Orange County beaches are mostly generated by local and distant winds. The height and length of these waves depend on three factors: wind speed, the distance it blows across the ocean surface and the length of time it blows. Here’s how waves are created:

Genesis

Wind blows across ocean’s surface, raising ripples, then chop. Waves continue to grow if wind continues, transferring energy by pushing directly against the wave backs. As waves grow steeper and higher, energy transfer between wind and water becomes more efficient.

Maturity

As newly developed waves leave their point of origin, they organize into lines of swell and move downwind. The original wind-driven waves disperse and new ones of greater length and speed form.

Landfall and Break

As waves approach land, they decelerate; lengths shorten and peaks form. As the ocean bottom becomes shallower, waves become critically steep and they break. The result: surf.

Waves and Measures

Surf forecasters use varied forms of technology, including international weather services, ship reports and National Oceanic and Atmospheric Administration weather charts. Data from ocean buoys is part of the data chain, helping clarify wave direction, height and interval. Here’s how they work:

1. Buoys move up and down and to and fro, recording and transmitting swell information.

2. Satellites receive size, direction and interval data every one to six hours.

3. Satellite data is relayed to the National Data Buoy Center in Mississippi

4. Data is sent to the National Meteorological Center in Maryland, then back to another satellite, whence it is available to forecasters.

Sources: Sean Collins, Surfline / Wavetrak, “A Book of Waves,” by Drew Kampion, “Waves and Beaches: The Dynamics of the Ocean Surface,” by Willard Bascom

Researched by DENNIS LOWE and TOM REINKEN/ Los Angeles Times