As Tropical Storm Hilary battered the West Coast and Southwest 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 (NOAA) Weather Prediction Center.

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

A tropical cyclone like Hilary setting rainfall records in four states is highly unusual, and only two other single tropical systems set rainfall records that came close to impacting 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 rainfall was the result of Hilary’s rare path through the states, where it first hit California, after making landfall on Mexico, and then traveled almost due north into the West and northern Rockies.

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

For Idaho, the previous record-setter was Olivia in 1982. Montana 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 of rain also from Kathleen in 1976, still stands after Hilary.

Hilary 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 state rainfall records due to 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 saw record rainfall from Cristobal in 2020 when remnants dropped 5.06 inches over the state. 

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By NBC News | The Informant