SAN DIEGO — As Hurricane Hilary continues its northward trek, southern California residents are bracing for an storm event unlike anything the region has seen in decades.

The dangerous storm system is currently graded by the National Weather Service as a Category 1 hurricane.

By the time it reaches California, meteorologists say the storm is likely to have weakened into a tropical storm, nonetheless brining “catastrophic” flooding and strong winds to the region.

This type of weather event is incredibly rare for the Golden State, with only a handful of storms managing to bring tropical storm-force winds in the last century.

Weather experts are revisiting two of these storm events in particular — a September 1939 tropical storm in Los Angeles and Hurricane Kathleen — to see how Hurricane Hilary might shake out.

Both of these events had monumental impacts on communities in the region, according to historians. Now, decades later, these storms could be useful for San Diegans to understand the impact that this unusual storm might have when it makes landfall on Sunday.

September 1939 Tropical Storm

In September 1939, Southern Californians were pummeled by four tropical cyclones that hit the region within weeks of each other. Each of the four made landfall at varying stages of cyclone development.

According to NASA historians, the first three storms were remnants of hurricanes with tropical storm-level winds, moving into the area after making landfall in Baja California — a similar path that Hurricane Hilary appears to be taking.

The most notable of the bunch was the fourth storm to make landfall in the region, touching down in Southern California on Sept. 25. The unnamed storm hit near San Pedro, according to NASA, becoming the first and only recorded instance of a tropical storm making landfall in the Southern California region directly.

Winds during the storm reached speeds as high as 50 miles per hour in the region, NASA said. The storm also brought upwards of five inches of rain to parts of the Los Angeles basin and 12 inches of rain to surrounding mountain areas.

Flooding due to the unprecedented levels of precipitation left thousands stranded in their homes. According to historians, some streets had standing water as deep as three feet.

Over 100 people were killed as a result of the final storm that month, according to National Oceanic and Atmospheric Association reports from the time. Roughly half died in flooding, while the other half drowned at sea.

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After the storm tore through the region, parts of Southern California were left with over $2 million — or an estimated $42.4 million based on 2023 inflation — in damages to structures and agriculture, NWS said.

While the Sept. 25 tropical storm had violent and devastating impacts, experts say much of this occurred due to how suddenly it came on, leaving residents generally unprepared.

Hurricane Kathleen

In mid-September 1976, a hurricane named Kathleen made its way to the southwestern U.S. after first making landfall in Baja California.

Similar to Hurricane Hilary, Kathleen weakened as it moved northward into California and Arizona, but it remained at a tropical storm strength when it hit the region.

California’s central and southern mountain communities saw the biggest impacts with the storm, according to NASA. Recorded precipitation ranged from about six to 12 inches in these areas, while sustained winds hit speeds of about 57 miles per hour.

Desert areas east of the mountains saw significant damages as a result of flooding, including about 70 to 80% of the town of Ocotillo in Imperial County. About twelve storm-related deaths were also recorded in these areas, NASA said.

According to experts, Hilary has the potential to play out similarly to Hurricane Kathleen, if it stays on its current track. However, the 1939 tropical cyclone remains an important framework to understand the potentially far-reaching impacts of the incoming storm.

Officials stress that taking Hurricane Hilary seriously could mean the difference between safety and devastation.

Residents are urged to shelter-in-place and to stay alert to emergency notifications, particularly if you live in a flood zone.