Airfare deals are taking off.

Discount airline Norwegian Air is offering airfares from the U.S. to Europe and other spots for under $100. One-way flights from New York to Martinique and Guadaloupe, France are $69, and for under $100 you can go to Dublin and Shannon, Ireland ($99) and Edinburgh ($89). Other cities you can travel to for $149 or less one-way from New York include Paris, Madrid, London, Copenhagen, Amsterdam and Stockholm. The airline also offers flights from Miami, Los Angeles, Las Vegas and other U.S. airports, though those tend to cost a little more.

Of course, there are caveats: To nab the deals, you have to book by Sept. 5, and travel between Oct. 31 and March 31, 2019. The super-low fares aren’t available every day of the week, and your return flight is likely to cost a little more, typically starting at about $109. And when booking low-cost fares in general, you must “make sure you understand the total cost of trip. Many of these fares will cost you extra for ancillaries like baggage and seat selection,” Patrick Surry, the chief data scientist at flight research and deal site Hopper, told Moneyish. Still, it can be a good deal, especially for those with flexibility on when they fly.

Even if you can’t catch this deal, this is a good time to book flights in general. Flight prices tend to drop in late August and early September, Tom Spagnola, the senior vice president of supplier relations for CheapOair, told Moneyish. Indeed, data from CheapOAir shows that “airfare will be at its lowest for a four-week period beginning the third week of August and lasting through the second week of September.”

The reason: “Prices and demand tend to peak in June for summer travel. Demand then weakens as the summer winds down, but holiday travel demand hasn’t quite ramped up,” explained Surry. “In order to entice travelers, the airlines will begin offering deals during this late summer/early fall period.”

So where are some of the best deals right now? In the coming weeks, expect “to see lots of deals to Europe that will be under $500 round-trip such as Paris, Iceland, Madrid, Stockholm, and Lisbon,” said Surry. That’s thanks to “the increased competition from low-cost carriers like Norwegian and Wow Air,” which is “leading to major discounts on these routes.” Plus, look for deals on some long-haul flights, he adds: “Prices to Shanghai are currently averaging $462 round-trip and prices to Singapore are currently averaging $553 round-trip.”

And don’t worry — the under-$100ish European deals are likely to pop up again. “We expect to see a lot more deals like this as we enter the fall,” said Surry.

Correction: An earlier version of this story noted that European flights started at $69 in the headline; this has been amended.