As many as 25 million passengers are expected to fly this Thanksgiving travel season, up from just under 24 million last year.

The estimate, part of the 2013 Thanksgiving Travel Forecast released today by the trade organization Airlines for America, represents a 1.5 percent increase over 2012 and covers the 12-day period from Friday, Nov. 22 through Tuesday, Dec. 3.

While there will be more travelers, there will also be more seats. Last year, planes were 90 percent full during the busiest days of the Thanksgiving travel season, but this year they are expected to be more than 85 percent full on the busiest travel days: the Wednesday before Thanksgiving, and the Sunday and Monday after the holiday, according to the forecast.

"More seats are returning to the marketplace to accommodate growing demand," said John Heimlich, vice president and chief economist of Airlines for America.

But for passengers, packed planes mean even less space for carry-ons and little wiggle room if there are weather-related travel issues.