UPDATE 1-Tropical Storm Teddy forms in the Atlantic - U.S. NHC

(Adds formation of Tropical Depression Twenty-One)

Sept 14 (Reuters) - Tropical Depression 20 has strengthened into storm Teddy in the Atlantic and is expected to become a powerful hurricane later this week, the U.S. National Hurricane Center (NHC) said on Monday.

The system is located about 1,110 miles (1,785 km) west of the Cape Verde Islands, packing maximum sustained winds of 40 miles per hour (65 km/h). It is expected to head west-northwest for one or two days before veering northwest, the NHC added.

A new tropical depression, Twenty-One, has formed about 330 miles (535 km/h) west-northwest of the Cape Verde islands, and is expected to be short lived, the Miami-based weather forecaster said. (Reporting by Diptendu Lahiri and Harshith Aranya in Bengaluru; Editing by Kevin Liffey and Louise Heavens)