After exploding in strength at a historic rate this weekend, Hurricane Erin is now a sprawling Category 4 storm churning in the Atlantic. The storm’s enormous footprint is becoming the biggest concern as it threatens to drive life-threatening rip currents and towering waves toward the eastern US coastline and Bermuda.

Forecasters are tracking a new disturbance in the Atlantic Ocean as Hurricane Erin, a Category 5 storm, undergoes an eyewall replacement cycle, according to a Saturday night update from the National Hurricane Center.

Reports from NOAA and Air Force Reserve Hurricane Hunter aircraft indicate that maximum sustained winds have increased to near 75 mph. Steady to rapid strengthening is expected during the next two to three days, and Erin is forecast to become a major hurricane this weekend.

Hurricane Erin formed Friday in the Atlantic Ocean on track to bring heavy rains that could lead to flooding and landslides in Puerto Rico and the Virgin Islands, forecasters said.

An area of low pressure is likely to develop into a cyclone within the next 48 hours, according to the National Hurricane Center.

The National Hurricane Center is predicting Invest 97L could become a tropical depression or tropical storm as early as later this morning, Aug. 11.