Hurricane Harvey’s catastrophic flooding could bump up gas prices for drivers.

The storm is expected to be the worst to hit the Gulf Coast, where 17% of crude oil in the U.S. is produced, on Saturday as gas companies scramble to prepare.

Refineries are already being shut down in anticipation of the Category 3 storm, disrupting gasoline supplies, and experts say you can expect an impact at the gas pump in Texas and some states because of it until the storm passes.

Wholesale gas rose Thursday by 5 cents, or 3%, to $1.66 per gallon, and will reportedly rise at service stations in the next few days. Drivers can expect an increase of 5 to 15 cents per gallon once the storm hits, and those numbers will rise by about 25 cents by Labor Day, The Associated Press reports.

The nationwide average price for regular gas rose one penny this week to $2.35, according to the The American Automobile Association. The average price was $2.19 per gallon a year ago.

When Hurricane Katrina hit in 2005, there was a 40-cent gas increase overnight. It’s unclear how great Harvey’s weather wrath will be until Monday, but meteorologists say power outages and excessive flooding are in the forecast.

So if you must drive, don’t waste gas.

Here are ways to save on gas ahead of the storm:

1. Get a gas app. Mobile maps for smartphones can help you save more than 20 cents per gallon. The free app Gas Buddy helps you locate the least expensive gas station, as well as the closest one in your proximity. And Fuel Finder automatically refreshes price data every five minutes, available for iPhones for $2.99.

2. Turn off the A.C. It may be hot, but air conditioning is the biggest gas guzzler. The AC can lower the fuel efficiency from 10 to 20% depending on the type of vehicle you drive and how old it is. Keep it off as much as you can, especially during the storm.

3. Drive manual. If you drive a manual transmission, shift up early on and shift down late to save on fuel. Be sure to shift into neutral when the car is still so you don’t overwork the transmission.

4. Avoid gas stations near the highway. The first service station you find, especially during the storm, is bound to be pricy. Avoid it by driving into the nearest town to find a cheaper station.

5. Fill your tires. Make sure your tires are fully inflated because if they’re not, they wear out faster and waste gas. Full tires reduce friction on the road and improve better gas milage.

6. Drive at a constant speed. If you drive an automatic transmission, try using cruise control to better manage your speed and conserve on fuel.