Delta is projected to have winds in the 125 mph range when it makes landfall along the Gulf Coast.
It's the strongest storm ever named after a letter in the Greek alphabet, eclipsing Hurricane Beta in 2005, which reached 115 mph.
Delta underwent rapid intensification Tuesday, which is defined as an increase of maximum sustained winds by at least 35 mph in a 24-hour period. In 36 hours, Delta went from a tropical storm to a Category 4 hurricane.
"Delta is the fastest storm to intensify from tropical depression to a Category 4 storm in modern records," said Michael Ventrice, meteorological scientist for The Weather Company.
The storm-weary Gulf Coast is in the cone of concern for the sixth time in the 2020 hurricane season.
Louisiana and Alabama have already declared a state of emergency ahead of the storm.
Delta is a relatively small storm with hurricane-force-winds extending 30 miles from the center and tropical-storm-force winds 125 miles from the center, according to the latest advisory.
"Our concern is storms like this tend to grow in size as they get into the Gulf of Mexico," AccuWeather senior meteorologist Dan Kottlowski said Tuesday. "Where this is a small hurricane it'll probably grow as it moves into the Gulf of Mexico, and with the core circulation like it has now when a storm gets bigger like that the core circulation, the eye, tends to get a title bit bigger and that kind of prevents it from really becoming any stronger than it already is."
Even though an eyewall replacement cycle might prevent Delta from getting much stronger, its increase in size could increase the wind field.
"It's probably going to be anywhere from 20 to 30% larger," said Michael Ventrice, a meteorological scientist at The Weather Company, "and this typically results in an expansion of the wind field compared to what it is as a smaller hurricane and a smaller eye."