Tropical storm Eta formed in the Caribbean late Saturday, tying the record for most named storms in a single Atlantic hurricane season.

The system reached maximum sustained winds of 65 km/h late Saturday, the U.S. National Hurricane Center said in an advisory. It's centred 435 kilometres southeast of Kingston, Jamaica.

Forecasters expect Eta to become a hurricane by Monday. The system is forecast to be near the northeastern coasts of Nicaragua and Honduras by Monday night. A hurricane watch was issued for parts of both countries. Eta was moving west at about 24 km/h.

Eta is the 28th named Atlantic storm this season, tying the 2005 record for named storms. However, this is the first time the Greek letter Eta is being used as a storm name; in 2005, after the season ended, meteorologists went back and determined there was a storm that should have gotten a name but didn't.

Hurricane season still has a month to go, ending Nov. 30. And in 2005, Zeta formed in the end of December.