Heavy rains from the powerful nor'easter pummeling the region today could cause flood levels in Rhode Island tomorrow not seen in more than two decades.

The Rhode Island Emergency Management Agency said this evening that it is closely monitoring the situation as forecasts call for up to 4 inches of rain as the snow changes over in the next few hours.

The rain is expected to cause major flooding in West Bay communities along the Pawtuxet River and minor flooding along the Blackstone River.

"There is a chance Saturday evening that we could have a major flood in Rhode Island," said Nicole Belk, a service hydrologist for the National Weather Service in Taunton, Mass. "This is a potent system. We’re expecting a prolonged period of heavy rain. That’s why we’re so concerned."

The forecast calls for up to 4 inches of rain across Rhode Island late tonight through tomorrow afternoon. The weather service has issued a flood watch, and Belk said it's almost certain that the Pawtuxet will reach at least 11 feet, which is the moderate flood stage.

If the rain totals 3 to 4 inches, Belk said the Pawtuxet should reach "major flood stage," which is 13 feet. Flooding in Warwick, West Warwick and Cranston later tomorrow could rival the floods of October 2005 that resulted in evacuations, submerged cars and several streets completely under water, she said.

The state emergency management agency notes that the Pawtuxet's expected 13.1- foot crest tomorrow at 8 p.m. could be the largest since April 1983. By comparison, the river crested at 10.5 feet when the river experienced flooding during heavy rains two weeks ago.

Minor flooding is possible along the Blackstone River basin, though Belk said rainfall total would be tempered by prolonged periods of sleet and freezing rain tonight. Coastal areas, however, should get all rain starting late tonight.

Belk participated in a conference call this afternoon with officials throughout the region as they decided how to prepare for the flooding.

The Blackstone Valley Tourism Council today urged some local businesses to set up sandbags to avoid serious flooding damage, according to the council's education coordinator, Patricia McAlpine. The council, like many local officials and agencies, has been in close contact with the weather service, McAlpine said.

"We suggest people keep checking the Web site and listening to radio reports," she said. "We know there's been a problem in the past with businesses in flood-prone areas."

A gale warning is also in effect for Rhode Island and Massachusetts coastal waters until 10 tonight, with northeast winds ranging from 25 to 30 knots and seas between 7 and 10 feet.

Belk urged motorists to avoid flooded roads. Cars shouldn't be parked in low-lying areas, she said. And drivers should avoid standing water on the road, as it's often far deeper than people think.

Earlier this month, a Providence woman's Lexus was swept into a small brook behind Roger Williams Medical Center during minor flooding. The Fire Department used a raft to reach the stranded driver and pulled her out through the car's sunroof.

Belk also urged residents to heed warnings from their local officials. If they decide to call for an evacuation, she said, people should do as they're told.

More into a flight mode? Check on the arrivals and departures of planes at local airports before you go. The storm, which is stretching across the Northeast, has caused cancellations and delays around the region.