Irma is expected to be downgraded to a tropical storm by the time it brushes by South Carolina Monday and into Tuesday, according to the National Hurricane Center, but heavy rains - up to 10 inches - and winds up to 50 miles per hour are possible.
"Remember, just because the winds have died down and it isn't raining any more does not mean its all clear", said McMaster. The remnants of the deadly hurricane are now projected to sweep into Alabama and Georgia by Monday morning, bringing strong winds and rain.
Columbia is most likely to experience the storm's effects throughout the day and night Monday, although tropical storm-force winds are possible starting Sunday night.
Patients in healthcare facilities in the counties of Jasper, Beaufort, Colleton, Dorchester, Charleston, Berkeley, Georgetown, and Horry were ordered evacuated as of 2 p.m. Thursday, the governor said.
"I'm real proud of the way that team SC has devised, through a lot of work and a lot of thought, a grand plan that so far is working extremely well", said McMaster.
McMaster said the rest of the state can evacuate if they don't feel safe.
Bulletin High School and Battery Creak High School in Beaufort County will open as shelters at 9 a.m. Sunday.
"Even so", Nicosia added in an email to the media and emergency managers, "there is way too much uncertainty this far out and we need to remain vigilant by being prepared in the event the storm track changes (and it could)".
Katia weakens to tropical depression over Mexico
Meanwhile, Hurricane Jose strengthened to Category 4, and hurricane watches were in effect for the northern Leeward Islands. The 8.1 quake off the southern Pacific coast just before midnight Thursday toppled hundreds of buildings in several states.
Meteorologists warned the surges could flood low-lying coastal areas, especially during high tide, damaging docks and piers and eroding beaches.
Major coastal flooding is possible, threatening to cut off many coastal areas, including routes to and from barrier islands.
The governor has rescinded part of his executive order calling for the evacuation of health centers along the coast.
Officials said the evacuation of medical facilities in Jasper, Beaufort, Colleton facilities is going well. These impact include storm surge, potential inland flooding and tropical storm force winds.
No other S.C. counties are under evacuation order.
Decisions on lane reversals in those areas will be made as needed.
"The largest cluster of solutions takes (Irma) west of the Appalachians to the Tennessee Valley by Tuesday evening", the weather service said in its 11 a.m.
County offices along with city of Georgetown offices will be closed Monday except for essential personnel.