Rachel and Kelvin Wave Combine to Threaten California Coast with Floods and Erosion

Key points

• Tropical Storm Rachel, downgraded from a Category 1 hurricane, is expected to bring widespread rain to Southern California from Saturday to Tuesday, with the highest chances between Sunday night and Monday.
• A Kelvin wave, fueled by El Niño, is raising sea levels by 6-12 inches and is expected to keep tides elevated for months, increasing the risk of coastal flooding and beach erosion.
• Forecasters see a 70-90% chance of rain in Los Angeles and Ventura counties, with peak flooding and significant beach erosion expected on Sunday, particularly in areas like Long Beach, Catalina Island, and the Malibu to Ventura coastline.
• The storm is expected to bring 0.25-0.75 inches of rain to most areas, with mountains receiving more, and is unlikely to cause debris flows or landslides due to low rain rates.
• NOAA has an 83% chance of a historic El Niño, which is driving the Kelvin wave and contributing to the unusually active hurricane season.

Background

This event follows a record-breaking heat wave in Southern California, which is expected to ease by Sunday or Monday. The current conditions are part of a broader trend of a historic El Niño, which has been raising sea levels and increasing the risk of coastal flooding and erosion. Previous coverage noted that a Kelvin wave had already begun to raise sea levels by up to a foot, compounding existing climate change trends and prompting emergency preparations across the state.

How outlets are covering it

The Los Angeles Times emphasizes the combined threat of Rachel and the Kelvin wave, highlighting the risk of significant beach erosion and coastal flooding, particularly on Sunday. KSL News focuses on the potential for heavy rainfall in Utah, which could help improve soil moisture and snowpack, but also warns of flooding risks. NBC 7 San Diego highlights the tropical storm watch for San Diego County, with potential for flash flooding, coastal flooding, and damaging winds. The Orange County Register reports on immediate flooding in Laguna Beach, with water covering streets and parking lots, and notes that the situation is likely to worsen over the next two weeks. The outlets differ in their emphasis, with some focusing on the immediate coastal impacts and others on the broader regional and long-term effects of the El Niño and Kelvin wave.

Why it matters

The convergence of Tropical Storm Rachel and the El Niño-driven Kelvin wave poses a significant threat to Southern California's coastline, with potential for widespread flooding, erosion, and damage to infrastructure. The event highlights the increasing risks associated with climate change and the need for preparedness and emergency response. The potential for a historic El Niño and the long-term elevation of sea levels by the Kelvin wave could have lasting impacts on the region's coastal communities and ecosystems.

What to watch

Forecasters expect the rain and flooding to continue through Tuesday, with the highest chances between Sunday night and Monday. The Kelvin wave is expected to keep sea levels elevated for months, increasing the risk of coastal flooding and erosion. The storm is expected to move through Utah, bringing heavy rainfall and potential flooding, but also helping to improve soil moisture and snowpack. The long-term impacts of the El Niño and Kelvin wave will depend on the strength and duration of the climate pattern, but the region is likely to face increased risks of flooding, erosion, and other weather-related hazards in the coming months.