Fetch winds created powerful waves that crashed over seawalls, leading to injuries, forced rescues, and significant water surges through the streets. Unexpectedly high waves, reaching up to 20 feet, struck the California coast on Thursday, causing havoc and catching bystanders off guard. 

Meteorologists from AccuWeather attribute these monstrous waves to specific conditions, and ongoing storms are expected to generate life-threatening surf throughout the weekend.

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Understanding Fetch Winds 

The phenomenon was triggered by an extended zone of winds known as fetch, allowing long-period swells to accumulate and build from multiple storms at sea.

These swells, driven by west-to-southwest winds, were propelled toward the California coast, resulting in the unexpected surge.

Long-period swells are closely tied to the strength and distance of winds over the open ocean. The energy from these swells, located just beneath the sea surface, generates larger waves as they reach shallow coastal waters compared to smaller breakers.

Distinguishing Swells from Tidal Waves

While the effects of Thursday's swells may resemble a mini tidal wave, they differ significantly. Tidal waves are not wind-generated; they result from a sudden vertical displacement on the sea floor. 

Unlike swells, tidal waves' energy is deep below the sea surface, making them potentially inconspicuous at sea but impactful when reaching the coast.

Although the extremely long fetch has diminished, a local storm approaching the Pacific coast is expected to create a significant swell, albeit potentially not as extreme as Thursday's event. Large breakers, known as sneaker waves, may develop and pose risks with minimal warning.

Experts advise against coastal activities due to life-threatening conditions, including pounding surf, powerful rip currents, coastal flooding, beach erosion, and potential structural damage. Small craft are urged to stay in port, and inexperienced individuals should avoid venturing into the surf.

Looking Ahead

While large swells and powerful breakers will subside from Sunday afternoon to New Year's Day, experts caution that the Northern Pacific's stormy conditions may lead to more rounds of significant surf in the coming months.

Vigilance and caution are paramount, as similar occurrences could occur later next week or during the first weekend of 2024.