This is just a guess but if a store owner is concerned
that he will have difficulty refilling his inventory
or if he thinks he may suffer extensive damage that
will prevent him from conducting regular business for
a time might he raise prices to get what he can, while
he can?
The store owner who is selling the generators has to cover a lot of fixed costs that don't change just because the area has been hit by a hurricane. He still has to pay rent, he still has to pay his taxes, he still has to pay his utility bills, and he still has to pay his staff.
If generators are the only thing anyone is buying in his store this week, he'd have to raise their prices simply to raise enough revenue to keep his store open.