Hurricane Erin was downgraded to a Category 3 storm Sunday, but forecasters warn it is expected to intensify and grow in size in coming days, as it lashes Caribbean islands with heavy rains that could cause flash floods and landslides.

Storms that ramp up so quickly complicate forecasting and make it harder for government agencies to plan for emergencies. Hurricane Erick, a Pacific storm that made landfall June 19 in Oaxaca, Mexico, also strengthened rapidly, doubling in intensity in less than a day.

As of 5:00 p.m. AST on Sunday, Erin’s center was positioned approximately 275 miles northwest of San Juan, Puerto Rico, tracking west-northwest at 13 mph. Although no longer directly affecting the area, the storm’s outer bands are still delivering heavy rainfall, dangerous marine conditions, and life-threatening surf along coastal areas.

An eyewall replacement cycle is underway within Hurricane Erin as the monster storm continues to barrel across the Atlantic while bringing gusty winds and rain to Puerto Rico and the Virgin Islands after rapidly intensifying into a catastrophic Category 5 hurricane over the weekend.

Erin is the first hurricane to develop over the Atlantic this year, and meteorologists are closely tracking its path and forecast.