The National Hurricane Center extended the forecast cone for an ongoing tropical cyclone – Hurricane Rachel – to California on Wednesday morning.
The storm will not be a hurricane by the time it approaches California this weekend, but it could still present the typical dangers of a tropical cyclone: heavy rain, strong winds, large waves and potential storm surge.
Officially, the hurricane center predicts the storm will make landfall about 100 miles south of San Diego around 5 a.m. Sunday, but the “cone of uncertainty” shows the possible path of the storm’s center as far north as Anaheim — a highly unusual potential incursion into California. The hurricane center notes that “hazardous conditions may occur outside the cone.”
The distant hurricane is already increasing the risk of dangerous rip currents across much of the Southern California coast. Heading into Saturday and Sunday, Orange and San Diego counties are most likely to experience strong winds and large, potentially destructive waves.
The National Weather Service is warning of a marginal risk (level 1 of 4) of heavy rain and flash flooding from Malibu to Los Angeles to San Diego on Sunday. There is a slight risk (Level 2 of 4) of flash flooding in Big Bear, Palm Springs, Las Vegas and Phoenix on the same day.
Forecasts may change significantly as the storm continues to evolve.
Hurricanes are fueled by warm ocean temperatures and their symmetrical, eye-shaped structure is a key feature. While ocean temperatures are warmer than normal off the coast of Southern California, the water is still too cold to support a full-blown hurricane. But symmetrical warm-core hurricanes can develop into messier “post-tropical” storms over the southwest United States while retaining their tropical moisture.
This process, known as extratropical transition, is most common in September and October during El Niño. This is also a complex process for weather models to resolve.
“There continues to be higher than normal uncertainty in the intensity of the latter portion of the forecast,” the hurricane center said. “Current forecasts show a post-tropical cyclone (Sunday morning), however, it is possible that there may still be tropical storm force winds at this point.”
That means sustained winds of 39 mph or higher are possible near the center of the storm, with even stronger gusts. The hurricane center puts the chance of tropical storm force winds in San Diego at less than 10%, but those risks could increase if the storm moves closer. Higher elevations will likely experience stronger wind speeds.
No recorded storm has entered California as a hurricane, but tropical storms have. Most recently, Tropical Storm Hilary narrowly missed landfall in California and passed through Mexico, but caused “significant flooding problems” in California’s deserts.
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