Hundreds of thousands without power in Oklahoma as severe thunderstorms continue throughout US

While tens of millions of Americans in the South are enduring a sweltering heat wave, another round of severe storms is threatening other parts of the region.

Nearly 300,000 customers across Oklahoma were without power following severe storms Saturday into Sunday morning, according to two of the state's power providers, Oklahoma Gas and Electric and the Public Service Company of Oklahoma.

Relentless rounds of severe thunderstorms continue to batter parts of the South this weekend, with thunderstorms expected to touch down from Arkansas to the Florida Panhandle from Sunday afternoon through the evening, forecasts show.

Strong, potentially damaging wind gusts and large hail remain the primary hazards of the latest sequence of storm systems, with the possibility of isolated tornadoes and frequent lightning.

The severe weather threat will linger across parts of the northern Gulf Coast region on Monday, focusing from the Mississippi coast and eastward across the Florida Panhandle, including cities such as Mobile, Alabama, and Tallahassee, Florida.

Any strong, slow-moving thunderstorms bringing torrential rain could trigger areas of flash flooding on Monday across parts of the Southeast, as well.

By early Sunday afternoon, nearly 300 reports of severe weather were issued from Colorado to Florida over the weekend. The majority of the reports detailed strong wind gusts, wind damage and large hail, as well as multiple tornado reports since Saturday. Most of the tornados were reported as either brief, weak or taking place in open fields.

Hail larger than baseballs was reported in multiple locations, including central Texas, the Oklahoma panhandle and southwestern Kansas, according to the National Weather Service. Numerous wind gusts topping 70 mph were reported across northern Oklahoma on Saturday evening, and Tulsa, Oklahoma, was hit hard with widespread wind damage and power outages reported in the city. Wind gusts up to 100 mph were reported there on Saturday night.

In Oklahoma, outages centralized in the Tulsa and McAlester metro areas were caused by severe weather, including wind gusts up to 90 mph that caused "sustained substantial damage to the grid including transmission structures, broken poles, cross-arms and downed wires," PSO said in a statement.

The outages are "the most significant restoration event" since an ice storm severely damaged the grid in 2007, PSO said, adding that it will take several days to recover power.

The system comes days after five people were killed as tornadoes rolled through Texas last week.

And another strong storm system could be approaching from the Atlantic in the coming weeks.

A tropical disturbance located several hundred miles southwest of the Cabo Verde Islands is showing signs of better organization and will likely develop into a tropical depression within the next 48 hours, forecasts show. The system will continue to move westward over the central Atlantic Ocean and could be near the Lesser Antilles by the end of the week.

ABC News' Nicholas Kerr contributed to this report.