The Harvest Fest happens annually near the United States Thanksgiving holiday.
The official description from the News post is:
"Every year, as the Fall comes to an end and nature has turned the colors of Earth into bright oranges and light browns, a Holiday called "Harvest Fest" begins. Harvest Fest is a time where Beasts from all corners of Earth give thanks for the many blessings of the year. Magnificent feasts are held in cities and towns and Beasts reconnect with friends and family.
Harvest Fest also marks the time in which flocks of Turkatrice begin migrating through Europe. These wild birds are the cornerstone of any traditional Harvest Feast, and so each year the great Turkatrice hunt begins as adventurers chase after these birds and return them to the local great Feast!
Harvest Masters can be found in the major cities of Camelot, Heartwood, and Bremen. Visiting these Harvest Masters for the first time will send you to a nearby chest where you can take your pick from any of the delicious foods available. You can also hunt local Turkatrices found in the wild and bring their meat back to the great feast in exchange for tokens that can be used to purchase additional Harvest Feast goodies.
But Turkatrice hunters beware, rumors dwell of a Turkatrice King who does not take kindly to the eating of his minions.
Purchase a special limited time only Turkatrice hat, available in the credit store!
Harvest Fest begins on Thursday, November 19th and runs until Wednesday, December 2nd!"