Relief for the embattled U.S. automotive industry is coming from an unlikely source: Hurricanes.

Research house Cox Automotive estimates the number of vehicles damaged by Hurricane Harvey in Texas at between 300,000 and half a million. Perhaps 20% will be repaired, and most of the rest replaced with secondhand vehicles, but at least some will drive new-car sales. On top of that there is the damage to vehicles on dealers’ lots, though Ford said last week this was less than 5,000 units for its brands, which are dominant in Texas. Hurricane Irma, which is now approaching Florida, could have a similar impact in the coming days.

Brokerage Evercore ISI puts the potential bump to 2017 new-car sales from Harvey at about 135,000, or a little under 1%. That wouldn’t be enough to restore the market to growth—sales are down 2.7% for the year through August, according to Autodata—but it would cushion the decline. The impact on profits in Detroit would also likely be greater, as Texans favor the lucrative pickups in which U.S. manufacturers specialize. Meanwhile, the rush of secondhand sales should support used-car prices. After Hurricane Katrina in 2005 used-car prices rose for half a year, notes Barclays. This is more significant for manufacturers than it sounds. Secondhand prices have been falling as cars bought new on lease three years ago hit dealer lots in ever greater numbers. The “residual values” that car makers’ finance arms and independent leasing companies include in their models are likewise falling, weighing on profits. They are compensating for this by tightening the terms of leasing packages, even as secondhand models get cheaper. This is an important reason why U.S. new-car sales are weakening—and likely to weaken further—despite near-record consumer confidence. Any support for used-car prices should slow this gradual erosion of the market. The storms won’t wash away Detroit’s long-term challenge of investing in electric and self-driving vehicles as demand in its crucial home market turns down. But insurance payouts may give U.S. car makers a much-needed late-year fillip. Write to Stephen Wilmot at stephen.wilmot@wsj.com

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