What San Diego Should Know About Hurricane Hilary

Editor’s note: We will update this post as we learn more.

Q. Will Hilary be a hurricane when it reaches San Diego County?

The latest forecast from the National Hurricane Center indicates that Hilary should lose its hurricane status (sustained winds of at least 75 mph) a few hours before it reaches the county. The entire county is under a tropical storm watch. The storm, as it moves north along the Baja California coast, could get within less than 100 miles of San Diego as a hurricane. But the weather service says there remains the potential for hurricane conditions off the coast on Sunday, with heavy seas, squalls and damaging winds.

The local weather service is using some of its strongest warning language ever: “Prepare for life-threatening rainfall flooding. … Devastating impacts across Southern California include numerous evacuations and rescues.”

Hilary keeps speeding up. The National Hurricane Center now has the center of the storm over central San Diego County by 6 p.m. Sunday. It’s still expected to be a tropical storm when it passes through.

Q. Has anything like Hurricane (or tropical storm) Hilary ever happened in San Diego before?

In some ways yes, in other ways, no. There is anecdotal evidence, from written reports, that a Category 1 hurricane with sustained winds of at least 75 mph hit San Diego on Oct. 2-3, 1858. There were no official measurements of the winds and rain, but significant damage was reported that suggested hurricane-force winds.

If Hilary delivers as much rain as forecasters believe, it could be the wettest tropical system in the city’s recorded history (reliable rainfall records go back to 1850). Preliminary estimates are for 2 to 2.5 inches of rain in San Diego. The most rain a tropical system has dropped on the city is 2.13 inches, from the remnants of former Hurricane Doreen on Aug. 16-17, 1977. Doreen dissipated around San Clemente Island, but not before causing flash floods in San Diego and Imperial counties. Four deaths were linked to Doreen.

Former Hurricane Kathleen arrived Sept. 9, 1976. Impacts in the city of San Diego were less substantial; it dropped less than an inch of rain. But the storm was deadly in the San Diego and Imperial County deserts. Kathleen arrived as a tropical storm, packing 57 mph sustained winds. It dropped a foot of rain in places, damaged hundreds of homes and killed 12 people. In terms of damage and impact, it has no rival in San Diego County.

Hilary has similar if not greater potential, if it stays on its current track.

Tropical-storm force winds hit Long Beach in September 1939, but they were not recorded in San Diego. 

Q. The usual mantra is that the waters off the Southern California coast are too cold to sustain a hurricane. They need to be around 79° or warmer. The ocean temp off La Jolla in recent days has been well below 70°. Why won’t Hilary break up before it gets here?

Hilary will encounter colder waters en route, and it will weaken. But Hilary has some characteristics that should allow it to outperform other tropical systems that have approached the area in the past. National Weather Service forecaster Miguel Miller said Hilary is huge, strong and moving fast. Early Friday it became a Category 4 storm, with sustained winds of 145 mph. It’s expected to max out at 150 mph. Tropical-storm force winds extend 250 miles from the center. Few storms, if any, have been that strong and that big so close to San Diego.

Miller compared Hilary to a giant bear chasing a person. A single arrow or shot will not subdue the bear. The cooler waters off our coast are not enough by themselves to keep Hilary from mauling So Cal. 

The storm’s speed is a big contributing factor. It’s moving fast and getting faster. If it were moving slowly, it would linger longer over the cooler waters near us, which would degrade the storm. Its speed should allow it to keep at least some of its circulation and storm structure until it’s well inland.

Q. When is the heavy rain expected to start?

The weather service says some light rain could start as early as Saturday afternoon, but the heaviest periods should be from late morning or early afternoon Sunday through early Monday.

Q. How much rain are the forecasters expecting inland?

Some of the projections from the forecast models are frightening. The inland valleys should get 2.5 to 3 inches of rain by Monday, but many locations in the mountains and deserts could get 5 to 7 inches. Some isolated spots could exceed 10 inches. That amount of rain is sure to cause flash flooding and road washouts. Avoiding travel anywhere in the county is advised, but especially in the mountains and desert.

Q. Have there been stronger hurricanes in the eastern Pacific?

There have been, but none have delivered the impacts that Hilary is expected to bring to San Diego. Hurricane Linda, Sept. 4, 1997, was the strongest eastern Pacific hurricane on record. It had sustained winds of 185 mph. Linda was initially forecast to strike San Diego, but it veered away. It brought only light rain to Southern California.