City of Charleston officials said they want citizens to be prepared for flooded streets and downed trees that Tropical Storm Andrea likely will bring tonight and Friday morning.

Mayor Joe Riley, at a press conference this afternoon, said city employees should not come to work until 10 a.m. Friday. There will be a high tide, and likely flooding, around 7:30 a.m., he said.

Tides will be slightly higher than normal today and Friday, Riley said, and the ground already is saturated from heavy rainfall. That makes flooding even more likely.

Charleston Police Chief Greg Mullen said officers Friday will barricade streets that have flooded and will reroute traffic. But, people should remember not to drive onto a flooded street, even if the entrance to it isn’t blocked.

“While this isn’t a hurricane, it’s a substantial storm we could be facing,” Mullen said.

Some areas in the city that typically flood are: the Crosstown, the streets around the Medical University of South Carolina, and Ashley and Rutledge avenues, Mullen said.

Riley said the city will post updated conditions on Facebook and Twitter, and will alert the media.

Tri-county emergency management officials also said their biggest concern about Tropical Storm Andrea is the impact of flooding.

Charleston County emergency management officials and their counterparts from Berkeley and Dorchester counties held a news conference this morning at Charleston County’s new Emergency Operations Center on Palmetto Commerce Parkway.

Charleston County moved to OPCON 4 at 10 a.m. That means there is the possibility of an emergency or disaster situation. And it notifies county employees who might be called in to work to be ready.

But the county hasn’t opened the Emergency Operation Center or called in those employees.

Maj. Jim Brady, spokesman for the Charleston County Sheriff’s Office, said drivers should only take to the road if necessary on Thursday and Friday because “areas prone to flooding will probably be flooded.”

Cathy Haynes, Charleston County’s director of operations for emergency management, said, “If there’s water on the road, don’t go through it.”

Charleston County Council Chairman Teddie Pryor said people should use common sense and not drive onto flooded roads.

And he asked employers to be flexible with their employees Friday morning. If the roads are flooded, people would be wise to wait before heading out to work, he said.

Nick Marino, from the Berkeley County Emergency Management Department, and Mario Formisano, from the Dorchester County Emergency Management Department, said they are working in a united front with Charleston County emergency officials.

Reach Diane Knich at 937-5491 or on Twitter @dianeknich.