UPDATE: Trump says a quarantine of the New York City area “will not be necessary,” CDC will issue a travel advisory instead
That’s a big deal. “CDC does not generally issue advisories or restrictions for travel within the United States.”
https://www.cdc.gov/coronavirus/2019-ncov/travelers/travel-in-the-us.html
Advisories give the receiving state powers, should a person decide to travel. Travel is allowed. CDC has the power to prohibit travel, but that power is a personal one, not a regional one.