Subtropical jet stream positions El Niño storms against Southern California coast

Meteorologists track seasonal shifts in atmospheric pressure that dictate storm tracks across the Pacific.

A powerful subtropical jet stream has formed between Hawaii and California. This high-altitude wind corridor is acting as a direct conveyor belt for moisture-laden storms heading toward the West Coast during the winter months.

The current El Niño event is injecting massive amounts of water vapor into the atmosphere. This moisture typically fuels stronger precipitation events and larger surf. When these storm systems align with the seasonally high tides known as king tides, the risk of coastal flooding increases sharply.

Phil Gonsalves, a forecaster with the National Weather Service, identified the recent weather pattern as a classic outcome of El Niño. San Diego County received approximately twice its normal October rainfall. A storm system moved into the region on Saturday night, delivering precipitation to the entire county before dawn on Sunday.

The jet stream responsible for this transport is intense. It stretches 200 to 300 miles in width and travels at speeds between 140 and 180 miles per hour. It operates at an altitude of 6 to 8 miles above the ocean surface. Storms forming within this zone are frequently termed pineapple expresses. Historical data shows these systems have caused widespread flooding and property damage in greater San Diego.

Brian D’Agostino, vice president of wildfire and climate science at San Diego Gas & Electric, noted that the weekend rainfall marked the first clear sign of this southern jet stream driving storms. The weather pattern signals a shift in how atmospheric moisture is being delivered to the region.

Marine conditions revealed the growing influence of El Niño earlier in the week. Morning high tides exceeded normal levels despite a lack of heavy surf or persistent winds. Tidal heights naturally rise from October through January due to Earth's proximity to the sun. However, this year's readings were further amplified by El Niño and a marine heat wave that affected the California coastline earlier in the year. The heat expanded the water volume, causing tide levels to rise. In La Jolla, ocean temperatures reached 75.4 degrees on Saturday, nearly 10 degrees above average.

Scripps Institution of Oceanography recorded a peak tide of 9 feet and 0.98 inches in La Jolla on Tuesday. This reading stands as the highest morning high tide in 102 years of record-keeping at that location. Reinhard Flick, a coastal oceanographer at Scripps, stated that the water level sat almost 1.5 feet above normal. He described the event as unprecedented for the local coast.

The elevated tides caused minor flooding in Point Loma, Pacific Beach, and Mission Beach. Water also backed up the drainage system along Harbor Drive in downtown San Diego. The pooling water on streets confused driverless Waymo vehicles, causing them to stall or reroute. The lack of strong winds and heavy surf prevented more widespread damage during that specific week.

The National Weather Service predicts additional king tides from November 24 to 26 and December 23 to 25. El Niño is expected to strengthen during these periods. Gonsalves cautioned that weather systems are not deterministic. While patterns are known, precise prediction remains difficult. He noted that nature has a mind of its own.