WATCH: FEMA director says not to underestimate the potential impact of Hurricane Ian

FEMA administrator Deanne Criswell issued a dire warning to Florida residents as they brace for Hurricane Ian, telling them “do not underestimate” the potential life-threatening impact of the storm.

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Ian tore into western Cuba Tuesday as a major hurricane, with nothing to stop it from intensifying into a catastrophic Category 4 storm before it crashes ashore Wednesday in Florida, where officials ordered 2.5 million people to evacuate.

Ian was forecast to strengthen even more over warm Gulf of Mexico waters, reaching top winds of 140 mph (225 kmh) as it approaches Florida’s southwest coast. Tropical storm-force winds were expected across the southern peninsula late Tuesday, reaching hurricane force Wednesday morning.

Criswell said by the time the storm reaches the shores of Florida, it is expected to slow down to approximately five miles per hour, which she said is significant in its potential for dangerous storm surge.

“What this means means is that Floridians are going to experience the impacts from this storm for a very long time,” Criswell said. “I can tell you that our biggest concern as we wait for this storm to make landfall is storm surge. And I will note that storm surge is a leading cause of hurricane related fatalities.”

LIVE MAP: Track the path of Hurricane Ian

With tropical storm-force winds extending 115 miles (185 kilometers) from Ian’s center, damage was expected across a wide area of Florida, regardless of where Ian makes landfall. The hurricane center expanded its storm surge warning to the peninsula’s Atlantic coast, and expanded its tropical storm warning from Boca Raton to Brunswick, Georgia — a distance of about 375 miles (603 kilometers).

Criswell said what makes storms like these particularly dangerous is their unpredictability. So she urged residents to listen to their local officials, heed their warnings and do not become complacent.

“Get ready and do not underestimate the potential that this storm can bring. Know where you are going to get your information, listen to your local officials and heed their advice. They are trying to keep you safe,” she said.