Hurricane Sally has made landfall on Alabama's Gulf Coast as a category two hurricane after winds intensified overnight.
Winds were clocked at 165km/h on Wednesday morning, able to cause extensive damage. The hurricane also poses the risk of "catastrophic and life-threatening" flooding along portions of the north-central Gulf Coast, the National Hurricane Center said in an advisory.
The NHC earlier said the hurricane could bring more than 60cm of rain to some areas as it creeps inland.
Sally made landfall at Gulf Shores, Alabama, and was creeping toward the Alabama-Florida border at 5km/h. Its winds and rains will stretch from Mississippi to the Florida Panhandle, the NHC said.
Officials across the South had called on residents of low-lying areas to shelter away from the winds and rain. But for some, Hurricane Sally's slow approach brought a chance to relive childhood memories of storms past, and to witness the power of nature first hand.
Thomas Harms braved the wind and rains on Tuesday to watch the waves crash into the Fairhope Municipal Pier, and reminisced about past storms. As a child, he went with his grandfather to see storms arrive, and he did the same on Tuesday for his son.
"It kind of takes a little bit of the fear out of it and also help you understand the dangers of it too," said Harms. "I've been kind of passing that on to my son in doing the same thing."
Damage from Sally was expected to reach up to $US3 billion ($A4.1 billion), said Chuck Watson of Enki Research, which tracks tropical storms and models the cost of their damage. That estimate could rise if the heaviest rainfall happened over land, Watson said.
Ports, schools and businesses were closed along the coast as Sally churned. As the storm track shifted east, ports along the Mississippi River were reopened to travel on Wednesday. But they were closed to vessel traffic from Biloxi, Mississippi, to Pascagoula, Florida.
Energy companies shut more than a quarter of US Gulf of Mexico offshore oil and gas production and some refiners halted or slowed operations.