Hilary – California’s first-ever tropical storm warning

Amidst a summer marked by extraordinary climatic events, an uncanny and terrifying forecast looms over the American Southwest this weekend: California’s first-ever tropical storm warning.

Hurricane Hilary, originating off Mexico’s western shores, is taking direct aim for Southern California, triggering another first-ever extreme weather warning, this time a Level 4/4 for rainfall. This hurricane, which had intensified to a Category 4 with sustained winds of 145mph/233kph by Friday morning, is predicted to continue to weaken as it slams into the Baja California peninsula in the wee hours of Sunday before reaching southern California later tomorrow as a tropical storm. Upon hitting California, this would be the state’s first such storm in nearly 85 years.

Whilst the winds may no longer be Category 4 upon landfall, forecasts from the National Oceanic and Atmospheric Administration’s Weather Prediction Center warn of the possibility of inland areas in Southern California receiving up to 2-3 years of rainfall in as many days. The potential for flooding throughout northwestern Mexico and southwestern US extends far beyond these projections and is partially driven by heightened storm surges associated with the winds.

Throughout Hilary’s track across northwestern Mexico and the southwestern US, the winds are expected to down trees and powerlines and cause significant property damage. The increased likelihood of rapidly intensifying storms such as Hilary can be attributed to climate change. As the oceans and atmosphere warm, they are able to feed more powerful storms with more intense rain. Storm surges are also increased due to sea level rise stemming from polar melt and thermal expansion from the warming ocean.

Although the Arctic is far away, both its glacial melt and its lessening ability to act as the world’s thermostat are driving sea level increases and ocean and atmospheric changes that are feeding the drivers and impacts of this storm.

If you’re in California, check out CalAlerts.org for critical updates affecting your area. Emergency tips for everyone in the storm’s trajectory can be found here from the American Red Cross.

Read more about extreme weather like this on our Global Risks page.

Image: Hurricane Hilary Barrels Toward Baja California – NASA