Texas, already soaked, may get hit hard from Patricia

Parts of north Texas, including the Dallas-Fort Worth area, were on alert as the National Weather Service placed several counties on flash flood warning.

Swathes of the central and eastern part of the state, as well as areas of Oklahoma, Arkansas and Louisiana bordering the Lone Star state were also on flash flood watch as the first trailing ends of Hurricane Patricia, currently lashing southwest Mexico, reached the U.S.' southern borders.

In the Houston area, CNN affiliate KTRK forecast 16 to 20 inches of rain, most of it falling Saturday evening to Sunday morning.

The main areas of heavy rain will shift from central and northeastern Texas eastward over the weekend, toward the Gulf Coast, the NWS said. Further showers and storms were due to develop and continue overnight into Saturday. The deluge follows months of drought, which has increased the dangers of flash flooding in Texas and the surrounding states.

The weather was affecting accessibility in some parts of the state, with the I-45 around the town of Corsicana, Texas, shut late Friday due to flooding, according to Texas Department of Transportation. The town is 55 miles south of downtown Dallas.

Flooding in the small town had left vehicles submerged, storm chaser Reed Timmer said on Twitter.

Elsewhere, social media lit up with photos of deluged streets across Texas.

The National Weather Service said an upper disturbance interacting with Hurricane Patricia in the Pacific had poured as much as 6.7 inches of rain across southeastern Oklahoma and parts of Texas since Thursday.

Still ahead: The potential for even heavier rains Saturday, especially for the eastern two-thirds of south-central Texas. Five to 10 inches of rain may fall in some areas, the weather service predicted. Western counties could see 1-3 inches of rain.

There's also a threat of isolated tornadoes Saturday when a low-pressure systems moves across the Rio Grande plains, the weather service said.

The Texas Division of Emergency Management urged rescue groups to have equipment and personnel in place in case of high-water rescues.

The Texas Task Force has provided 11 rescue swimmers for helicopter search-and-rescue teams and has seven water-rescue boat squads positioned along the I-35 corridor, a press release said.

Flash-flood warnings were up in parts of the region Friday afternoon, with broader flash-flood warnings covering parts of Texas and Oklahoma into the weekend.

In Louisiana, the weather service said the greatest threat was street flooding during periods of heavy rain and coastal flooding.

The threat of floods may sound like a deadly replay for Texans.

In May, heavy rains caused floods that killed at least 15, plus at least six in Oklahoma.

This year, much of east Texas — and all of northern Louisiana, southern Arkansas and west-central Mississippi — have suffered through extreme or exceptional drought, the two highest classifications, according to the U.S. Drought Monitor.