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.

The storm will remain a major hurricane through the middle of the week, according to the National Hurricane Center.

Hurricane Erin has re-intensified into a category 4 storm on Sunday after completing an eyewall replacement cycle, with the U.S. National Hurricane Center warning of life-threatening surf and rip currents along the U.

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.

Tropical Storm Erin is likely to become Hurricane Erin shortly. It's now tracking over ocean water that's in the low 80s, and the dry and dusty air that has had a stranglehold on the circulation is dissipating.