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Four states broke rainfall records because of Tropical Storm Hilary

Idaho, Montana, Nevada and Oregon broke their rainfall records, NOAA said.
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As Tropical Storm Hilary battered the West Coast and the southwestern U.S. with rain and flash flooding, four states — Idaho, Montana, Nevada and Oregon — broke their rainfall records, according to the National Oceanic and Atmospheric Association’s Weather Prediction Center.

In Nevada, the record more than doubled, to 9.20 inches, while Montana, Idaho and Oregon all got up to an inch more rain compared to the previous records. 

A tropical cyclone like Hilary's setting rainfall records in four states is highly unusual, and only two other single tropical systems have set rainfall records that came close to affecting as many states. Carla in 1961 set rainfall records across Iowa, Wisconsin and Michigan, and Kathleen in 1976 set records across California, Oregon and Idaho.

The widespread rain was the result of Hilary’s rare path through the states, where it first hit California after having made landfall on Mexico and then traveled almost due north into the West and the northern Rockies.

People drive through floodwaters following Tropical Storm Hilary in Thousand Palms, Calif., on Aug. 21, 2023.
People drive through floodwaters following Tropical Storm Hilary in Thousand Palms, Calif., on Aug. 21, 2023.Josh Edelson / AFP - Getty Images

Forecasters had predicted that because of the high amounts of deep tropical moisture transported into the region, record-setting rainfall would be likely, breaking daily records, monthly records and even state records.

For Idaho, the previous record-setter was Olivia in 1982. Montana’s and Oregon’s records were from the same tropical system, Kathleen, in 1976. Nevada had the oldest record of the four states, from an unnamed tropical system in 1906. 

The state record for California, at 17.76 inches also from Kathleen in 1976, still stands after Hilary.

Hilary’s setting records in four states brings the number of new records up to nine in just the past six years, and research continues to attribute heavier rainfall rates and amounts produced by tropical cyclones to climate change.

That means historic rainfall could become more common, and since 2017, five other states have broken records because of tropical systems.

Hurricane Harvey set the Texas record in 2017 when it dropped 60.58 inches of rain over the state. Hurricane Florence in 2018 set records across both North Carolina and South Carolina; Barry in 2019 dropped a record amount of rain, more than 16 inches, over Arkansas; and Minnesota got record rainfall from Cristobal in 2020, when remnants dropped 5.06 inches over the state.