NEW YORK – Drivers are being hit with the biggest one-day jump in gasoline prices in 18 months just as the last heavy driving weekend of the summer approaches.

As Hurricane Isaac swamps the nation’s oil and gas hub along the Gulf Coast, it’s delivering sharply higher pump prices to storm-battered residents of Louisiana and Mississippi – and also to unsuspecting drivers up north in Illinois, Indiana and Ohio.

The national average price of a gallon of gas jumped almost five cents Wednesday to $3.80, the highest ever for this date. Prices are expected to continue to climb through Labor Day weekend, the end of the summer driving season.