Rachel could bring San Diego up to 2½ Octobers’ worth of rain in a day

October is usually one of San Diego’s quietest rain months. This weekend, the remnants of Tropical Storm Rachel could change that in a single day.

The National Weather Service office in San Diego expects 0.40 to 1.25 inches of rain on the coast and in the valleys, with the highest totals in southeastern areas and more in the mountains. For perspective, the official San Diego gauge at the airport averages half an inch for the entire month of October.

What’s coming from Rachel

Rachel is a tropical storm, not a hurricane. At 2 p.m. Saturday, the National Hurricane Center placed its center about 400 miles south of San Diego, moving north-northeast at 30 mph with top sustained winds near 65 mph. NHC expects the center to move onshore over northern Baja California tonight and become post-tropical by Sunday morning as its remnants cross the Southwest.

A Tropical Storm Watch covers the San Diego County coast, and the NWS has a Flood Watch for San Diego County from this evening through Sunday evening. Forecasters expect light rain to turn moderate to heavy around midnight in San Diego County, with the heaviest and most widespread rain for most places before noon Sunday.

Here’s what NWS San Diego’s Saturday midday forecast discussion expects from Rachel:

Forecasters say areas of flash flooding are possible Sunday, and they expect the San Diego River at Fashion Valley to peak around 7.5 feet near noon Sunday, which the NWS lists as action/monitor stage. Scattered showers could linger near the coast into Monday before drier, warmer weather returns.

How this October stacks up

October rain in San Diego tends to come in one or two events, or not at all. In 2021, a pair of early storms and a late-month system added up to 1.01 inches. In 2022 and 2023, the airport barely got wet. October 2024 recorded only a trace, and last October brought 0.41 inch, nearly all of it on Oct. 14.

That’s why a single tropical system can swing the month so dramatically. The low end of the forecast would land just under a normal October. The high end would be about two and a half times normal, and not far from the 1.52 inches the past five Octobers produced combined.

San Diego’s normal October rain is half an inch. Rachel could bring up to two and a half times that in about a day.

How rain is measured here

When you hear “San Diego got X inches,” that number almost always comes from the National Weather Service’s official weather station at San Diego International Airport, long known as Lindbergh Field. It’s an automated station that measures rainfall continuously, down to the hundredth of an inch.

“Normal” has a specific meaning, too. NOAA calculates climate normals as 30-year averages and updates them periodically. The current set covers 1991 through 2020, and it puts San Diego’s normal October at 0.50 inch and the full year at 9.79 inches. Older references may use a different period and show different numbers.

Rain totals also vary across the county, and the same storm often drops more in the foothills and mountains than at the coast. The County of San Diego’s Flood Control District runs its own real-time network of gauges, called ALERT, that sends readings from around the county to its weather center in Kearny Mesa. It’s a good way to see what fell closer to you.

One more thing to know: San Diego’s “rain year” doesn’t follow the calendar. Water years start Oct. 1, so any rain Rachel delivers counts toward the new water year that just began.

Before the rain arrives

The NWS warns that urban flooding and flash flooding in the mountains are possible, and the coast is already under a Coastal Flood Warning through 3 p.m. Sunday because of high tides and surf. Clear gutters and drains, avoid flooded roads and low crossings, and check NWS San Diego and AlertSanDiego for updates. For the latest track, see our Tropical Storm Rachel story.