The outer bands of the storm are expected to dump 2 to 4 inches of rain in the Florida Keys, the Yucatan Peninsula, Belize and Northern Honduras.
An Air Force Reserve Hurricane Hunter aircraft is now en route to investigate Michael.
AccuWeather added in a report that rain and gusty winds are expected to ramp up across the central and/or northeastern Gulf Coast around midweek.
Forecasters are calling on Florida Gulf Coast residents to monitor the storm's approach, warning of the possibility of storm surge, heavy rains and unsafe winds as it approaches the U.S. Southeast.
Michael is forecast to strengthen into a Category 2 hurricane before it makes landfall near Appalachicola, FL with 100 mile per hour winds before quickly losing strength as it moves over the Southeastern United States.
Scott, who announced he was declaring a state of emergency Sunday for 26 counties in the Florida Panhandle and Big Bend, said that afternoon that the storm will be slow, strong and will bring a unsafe storm surge."This storm will be life-threatening and extremely risky", he said in briefing Sunday evening.
Michael has undergone a period of "rapid intensification" - defined as an increase of sustained winds of 35 mph in a 24-hour period.
"The FL panhandle needs to be prepared for a direct hit with sustained hurricane force winds", Scott wrote on Twitter on Monday.
Some strengthening is forecast during the next several days, and the depression is expected to become a tropical storm later today.
The storm is expected to unleash coastal storm surges of up to 12 feet (3.7 meters) along Florida's Panhandle and dump as much as a foot (30 cm) of rain across Florida, Georgia and SC, the National Hurricane Center (NHC) reported.
Scott warned that Michael could reach land as a Category 2 hurricane with winds in excess of 100 miles per hour. Tropical storm winds extended out 170 miles (275 kilometers), primarily to the northeast and southeast of the storm's center.
Cuban officials issued the warning for the provinces of Pinar del Rio and Isle of Youth.
Forecasters predicted Michael would be a major hurricane - Category 3 or stronger - by the time it arrived Wednesday.
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