It could be the first time two hurricanes form in the Gulf of Mexico simultaneously, according to records dating to at least 1900.
Tropical Storms Laura and Marco were both projected to approach the U.S. Gulf Coast at or near hurricane force.
At least nine people were killed, including a 5-year-old girl, and millions of others were left without power.
Millions of people were without power on Wednesday after felled trees downed power lines.
Roads flooded in coastal Louisiana and Mississippi, and thousands were without power even before the the storm made landfall.
Bertha's maximum sustained winds were near 50 mph as it came ashore but it was expected to weaken to a tropical depression after moving inland.
Arthur formed Saturday in waters off Florida, marking the sixth straight year that a named storm has developed before June 1.
Tropical Storm Dorian is bearing down on Puerto Rico, which is still recovering from 2017's Hurricane Maria.
The slow-moving storm could bring up to 25 inches of rain to some parts of the South, and it may become a hurricane as early as Friday.
Tropical Storm Michael could strengthen into a hurricane by Tuesday night or Wednesday, the hurricane center said.