By Cherri Gregg, Elizabeth Hur

PHILADELPHIA (CBS) — Delaware Governor Jack Markell has issued a partial state of emergency for the state beginning Saturday night.

“The prudent thing for us to do here,” said Markell, “is to have people leave many of our coastal communities.”

Governor Markell says the partial state of emergency will last for a period of 24 beginning at 8 p.m. on Saturday.

“I’m ordering a mandatory evacuation of coastal communities in Sussex, Kent and New Castle Counties,” he said. “All of the above have been identified to us by emergency management officials.”

Markell says all residents in flood-prone areas must be evacuated by 8 p.m. on Sunday. He says evacuees needing shelter should wait until Sunday at noon to head to shelters in all three counties.

The Governor says significant flooding and power outages are expected, and those who stay will be left without access to first responders.

Earlier in the day, Wilmington Mayor James M. Baker declared a state of emergency effective at 3 p.m. Saturday. (read related story:)

The evacuation order applies to about 3,000 residents who live in a flood plain area of the city.

For a list of communities impacted and shelters go to delaware.gov or at 1800-464-HELP.