The U.S. National Hurricane Center said Roslyn's maximum sustained winds had increased to 130 mph and it was expected to grow still further.
The storm has landed in South Carolina after devastating southwest and central Florida. Ian brought heavy rain, high winds and flooding along South Carolina coast, causing damage in some areas.
"The flooding has been catastrophic," the police department on Pawleys Island, S.C., said around midday. As the storm arrived, the state was under 85 weather alerts.
The category 4 storm had sustained winds of 150 mph, just shy of category 5 status, before making landfall in Lee County.
Such massive storms are fairly rare, and it's even more rare for them to make landfall. NOAA says that for such storms, "catastrophic damage will occur" with electricity outages "for weeks or months."
The National Weather Service's Joel Cline wants residents to know when danger is coming. But he adds, "If people think of a hurricane as a dot and a city as a dot, I think they've missed the point."
The weather system currently churning south of Jamaica is projected to intensify into a hurricane in the coming days. Gov. Ron DeSantis declared a state of emergency in Florida.
"Things are all upside-down," making it hard for hurricanes to form, an expert says. But experts warn not to assume there's less risk just because the first months of hurricane season have been calm.
For decades, it was impossible to say that a specific weather event was caused, or even made worse, by climate change. But advanced research methods are changing that.