Tropical Storm Bertha strengthened in the Gulf of Mexico and was moving slowly toward the Florida Panhandle and Alabama, causing a tropical storm warning and storm surge watches, forecasters said.

The storm was about 125 miles (201km) south-east of Mobile, Alabama, the Miami-based National Hurricane Center (NHC) said on Tuesday afternoon. It was moving north-west at 5mph (8km/h) with maximum sustained winds of 60mph.

The wind speed increased by 20mph since Bertha formed on Monday night. A tropical storm warning, meaning the conditions are expected within the warning area within 36 hours, was in effect early on Tuesday from the Florida and Alabama border to the Jefferson and Plaquemines parish line in Louisiana.

A storm surge watch, indicating rising, possible life-threatening water moving inland from the coast within 48 hours, was issued from the Alabama and Florida border to the mouth of the Mississippi River, the NHC reported.

Bertha is the second tropical storm of the Atlantic hurricane season after Tropical Storm Arthur brought heavy rainfall to the south-eastern US in June.

The storm was expected to stay near or along the northern Gulf coast, dropping heavy rain on coastal areas of Florida, Alabama, Mississippi and Louisiana while pushing west toward Texas.

Potentially life-threatening storm surges of up to 4ft (1.2 meters) are possible in portions of Louisiana, Alabama and Florida, the NHC said, warning Bertha could spin off an isolated tornado or two over the Florida Big Bend region.

Areas of flash flooding also were possible through Friday along the coast from western Florida to middle Texas, forecasters said, adding that rainfall could total 3in to 5in (7cm to 12cm) along the Louisiana coastline, with higher amounts in some scattered areas.

Red flags on the beach at Orange Beach, Alabama, cautioned swimmers about high surf and currents. In Escambia county, Florida, emergency officials offered sand for people living in flood-prone areas to use for sandbags.

Meanwhile, in the eastern Pacific Ocean, Hurricane Fausto churned far from Mexico’s Baja California peninsula and posed no threat to land, the NHC said.

Fausto gained hurricane status on Monday night. It was about 740 miles south-west of the southern tip of the Baja California peninsula, had top sustained winds of 80mph and was moving north-west at 12mph.

The storm was expected to strengthen on Tuesday and Wednesday. No coastal watches or warnings were in effect, though ocean swells generated by the storm could cause life-threatening surf and rip tide conditions on the Baja California coast, the NHC said.