Tropical Storm Erin hasn't gained much strength since forming on Monday over the Atlantic, but the National Hurricane Center says that should change soon as the storm moves west toward more favorable conditions for development.

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.