Tropical Storm Erin slows to 17 mph but is expected to become a hurricane by Friday, likely tracking east of the U.S. East Coast.

Erin developed in the eastern Atlantic, moving westward from the Cabo Verde Islands at about 20 mph (32 km/h). Infrared sensors on NOAA's GOES-19 satellite reveal colder cloud tops and deep convection near the center — signs of a strengthening system feeding on warm ocean waters.

Tropical Storm Erin has formed on a path toward the Caribbean and is expected to strengthen to a hurricane later in the week as it passes by Puerto Rico. Most models forecast the storm turning upward into the Atlantic Ocean, but a few see the storm continuing onward to the U.S. mainland.