Heavy rains were forecast to start late Friday in Antigua and Barbuda, the U.S. and British Virgin Islands, and southern and eastern Puerto Rico. Up to 4 inches (10 centimeters) are expected, with isolated totals of up to 6 inches (15 centimeters), according to the National Hurricane Center in Miami. Forecasters also warned of dangerous swells.

Tropical Storm Erin is forecast to strengthen into a hurricane on Friday as it tracks north of the Caribbean and intensifies into a major Category 3 storm. Here’s the latest forecast.

The key to the severity of impacts in the Leeward Islands and Puerto Rico from strengthening Erin depends on how soon a turn to the northwest occurs with a near-miss versus a direct hit.