Tropical Storm Zeta forms in the open Atlantic Ocean, tying the record for the latest tropical cyclone ever to form in the North Atlantic basin.

Tropical Storm Zeta was a very late-developing tropical storm that formed in the central Atlantic Ocean during the 2005 Atlantic hurricane season, forming one month after the season's official end. Becoming a tropical depression on December 30, and intensifying the following day into the season's 28th storm, Zeta continued into January 2006. It was one of only two Atlantic tropical cyclones to span two calendar years.

A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon is the same thing which occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn or more.