National Weather Service San Diego Issues First Tropical Storm Watches/Warnings for Extreme Southwestern California for Tropical Storm Hilary

National Weather Service (NWS) forecast offices in San Diego (SGX) and Los Angeles/Oxnard (LOX) became the agency’s only tropical capable forecast offices in the western United States at the beginning of the 2023 Pacific Hurricane season. NWS SGX and LOX gained the ability to issue Tropical Cyclone Local Watch/Warnings (TCV), Hurricane Local Statements (HLS) and Hurricane Threats and Impacts (HTI) for any impending tropical storm or hurricane to approach Southern California. The addition of the tropical suite of products came just in time, months ahead of Tropical Storm Hilary which made landfall in the northern Baja Peninsula shortly before crossing into California.

In the middle of August, tropical development looked possible off the southwestern coast of Mexico. Southern California is no stranger to impacts from distant tropical disturbances as well as remnants from previous hurricanes, but a direct landfall in northern Baja California or somewhere along the Southern California coastline looked possible from Tropical Storm Hilary. Close coordination with the National Hurricane Center (NHC), the Weather Prediction Center (WPC), the Ocean Prediction Center (OPC), and neighboring NWS forecast offices occurred leading up to landfall. As landfall miles from the border of California looked more likely, the need for Impact-Based Decision Support Services (IDSS) increased significantly at NWS SGX. The team conducted numerous live webinars with local emergency management partners; hundreds of interviews with local, national, and international news agencies; issued specialized partner briefings; and communicated with the public via social media.

Using the recently implemented tropical procedures, SGX and LOX issued the first ever Tropical Storm Watches and Warnings on August 18 along the West Coast. Tropical Storm Hilary made landfall in northern Baja California on August 20, 2023, and moved northward through Southern California that afternoon and evening. Tropical Storm Hilary produced torrential rainfall across mountain and desert communities resulting in catastrophic flash flooding and debris flows, and widespread tropical storm-force winds.

This presentation will focus on tropical operations at NWS SGX leading up to Tropical Storm Hilary including coordination and collaboration efforts with partnering agencies, challenges with the forecast and messaging via IDSS, rain and wind impacts across Southern California, and lessons learned along the way.