Erin is the fifth named storm to develop during the Atlantic hurricane season, which started just over two months ago. Last week, Tropical Storm Dexter formed in the western Atlantic but didn't pose a threat to land. In early July, Tropical Storm Chantal made landfall on the Carolina coast, bringing deadly flooding to the region.

As Erin continues to churn over very warm water, the storm will gain quick momentum and will likely become the first major hurricane (a category 3, 4 or 5 storm) as early as this weekend as it passes to the north of Puerto Rico.