SAN FRANCISCO – California declared a state of emergency Wednesday as a powerful storm generated 45-foot waves out at sea, dropped soaking rain on already saturated ground and prompted warnings of floods and mudslides.

The storm’s impacts will ramp up during the afternoon and the more than 8 million people who live in the San Francisco Bay Area should limit travel, the regional National Weather Service office warned. Earlier in the day, Gov. Gavin Newsom authorized state National Guard units to support disaster response as a massive storm pummeled much of the state’s coastline.

Fire and rescue equipment and personnel have been prepositioned in areas deemed most likely to experience severe flooding and mudflows.

GRAPHICS: ‘Rivers in the sky’: Graphics show atmospheric river soaking California’s Bay Area

“If you’ve still got power, it’s a good idea to charge your cellphone, computers and tablets now while you can,” said National Weather Service meteorologist Cynthia Palmer in the agency’s San Francisco area office. If the power goes out, having access to timely information about the storm – and something to watch – will be useful, she said. 

The storm is termed a “bomb cyclone” because it is expected to be marked by a quick drop in atmospheric pressure resulting in a high-intensity storm.

“All told it’s about a 30-hour event from start to finish,” said Rick Canepa, a meteorologist with the National Weather Service’s San Francisco office. “The rain won’t be done until Thursday afternoon or early evening.”

But officials warn even then the danger isn’t over. Forecasters are watching other systems out at sea that could also hit the region with more precipitation.

Meanwhile, California wasn’t the only place facing severe weather on Wednesday. A possible tornado touched down near Montgomery, Alabama early Wednesday. There were no deaths but the twister damaged more than 50 homes.

In San Francisco, customers at Papenhausen Hardware were most worried about flooding, said store co-owner Karl Aguilar.

“Last week a fair amount of people were focused on the roofs – small leaks, windows, things like that,’’ Aguilar said. “There was a point where it transitioned and people became much more concerned with flooding mitigation. This particular storm, it’s all flood mitigation.’’

A few doors to the east, Grace Daryanani at Bulls Head restaurant has sandbags and wet/dry vacuum cleaners at the ready. Her space has flooded in big storms before but she’s hoping a new outdoor dining area might divert some of the water.

“Maybe that will help,” she said. 

Wednesday commute worries

The afternoon commute was of special concern in the San Francisco Bay Area as it will come just as strong bands of wind and rain start to arrive ashore.

“There could be a lull in the rain and a false sense that it’s not that bad. But it’s coming. Trust me, it’s coming,” Palmer said. 

Coastal flooding could also occur during the high tides over the next 24 hours, which will come at 11:37 p.m. Wednesday night and 9:41 a.m. Thursday morning.

“We’ve got so much wind over the ocean that’s pushing water towards the coast,” she said.

LEARN MORE: What is a bomb cyclone?

WEATHER TERMS: What is an ‘atmospheric river’?

The monster storm, carrying tremendous amounts of rain, extends from as far south as Los Angeles to as far north as the Oregon border, but the bulk of the rain and wind are occuring  in the central and northern part of California. 

Forecasters warned of flood threats and issued high wind warnings in the lead-up to the storm. The National Weather Service in the Bay Area delivered a rare admonition saying the coming “brutal” storm system “needs to be taken seriously.” 

“Honestly, the biggest story right now is the winds,” said Palmer. Coastal areas could be hit with winds in the 40 to 50 mph range, while some mountain areas could get gusts as high as 80 mph.

Severe weather could drop 10 or more inches of rain in some parts of Northern California over the next week, forecasters say. Wednesday’s storm was expected to knock down trees, cause widespread flooding, wash out roads, cause hillsides to collapse, slow airports and potentially lead to the “loss of human life,” the National Weather Service said.

Flooding and landslides likely

Because the ground was already saturated with the more than 5 inches of rain that fell on New Year’s Eve, Wednesday’s storm could cause severe problems and damage in some areas.

“The main concern is the smaller watersheds and steep slopes. So mudslides, shallow landslides and urban and small creek flooding could get quite significant for a period of time on Wednesday night in some locations,” said Daniel Swain, a climatologist at the University of California, Los Angeles.

Severe weather, possible tornadoes in South

The South, too, was being hit with intense weather Wednesday. Heavy rains, flash floods and severe weather were seen in a swath across Florida, Georgia, North and South Carolina.

A possible tornado touched down in east Montgomery, Alabama at 3:14 a.m. on Wednesday. 

Rodney Penn, who was home when the storm hit, said a fallen tree limb broke out the windows in his wife’s car but there was no structural damage to his apartment.

“It literally sounded like there were a thousand baseball bats hitting the side of the house at the same time,” Penn said. 

In South Carolina, five counties were under a tornado watch Wednesday. 

Heavy rain in California not an end to drought in West

The extreme drought conditions California has struggled under are helping avert some possible flooding because many of the state’s larger reservoirs are still quite low, said Swain.

“They have a lot of headroom right now to absorb a lot of water,” he said. 

The state finds itself in the middle of a flood emergency even as it’s in the middle of a drought emergency, Karla Nemeth, director of the California Department of Water Resources said during a news conference Wednesday.

“A lot of our trees are stressed after three years of intensive drought, the ground is saturated and there is a significant chance of downed trees that will create significant problems, potentially flooding problems, potentially power problems,” she said.

While the rains are likely to alleviate the short-term drought in northern California along the coast, they will do little in terms of bringing drought relief to the West as a whole.

“It won’t really help move the needle in the Colorado basin but it certainly will in central and northern California,” Swain said.

More water is on the way

There are two more possible storms also out in the Pacific, one that could arrive late Friday and run into Sunday and then another possible storm that could arrive Tuesday, Canepa said. 

Both could bring higher-than-normal rain levels through the middle of January. 

There’s a wide range of uncertainty for next week, ranging from a couple of additional moderate storms which wouldn’t cause too many problems to one or possibly more atmospheric river events.

What’s an atmospheric river?

The storm, the second of three or possibly four headed toward the California coast, is coming from across the Pacific ocean. It’s what’s known as an atmospheric river or, to use the term more common a few years ago, a Pineapple Express because it originates over Hawaii.

These storms bring heavy rainfall and occur when a line of warm, moist air flows from near the islands across the Pacific Ocean to the West Coast.

When it reaches the cooler air over the western landmass, the water vapor falls as heavy rain. Atmospheric rivers are long, flowing regions of the atmosphere that carry water vapor across a swath of sky 250 to 375 miles wide. They can be more than 1,000 miles long – and can carry more water than the Mississippi River. 

Contributing: Dinah Puler in Florida, Evan Mealins and Alex Gladden, Montgomery Advertiser