Hurricane forecasters' worst nightmare came true on Wednesday morning, when what had been a Category 3 storm Tuesday night suddenly jumped almost to Category 5.

Why it matters: It used to be rare for storms to keep strengthening until landfall, let alone do so rapidly. Now it is not — and studies show this is a dangerous sign of climate change.

The big picture: Such an intensity leap was made possible by warm ocean temperatures and abundant atmospheric moisture — both factors that climate change enhances.

It's not just the U.S. that has been suffering the consequences from rapidly intensifying tropical cyclones. Consider an example from halfway around the world, which occurred just as Ian was spinning up in the Caribbean.

Threat level: The danger of a rapid intensification shortly before landfall is that people will be caught off guard by the stronger storm, and get stuck in a vulnerable spot for storm surge flooding, damaging winds or both.

Between the lines: The trends seen in the past several years, together with studies of how hurricanes are changing in a warming world, point to a key role for human-caused climate change.

Yes, but: While forecasters have made great strides in predicting storm tracks several days in advance (though the Ian track forecast was more uncertain than most), intensity forecasts have been stuck.

The bottom line: There is research underway to better predict intensity shifts, using new technologies such as Saildrones, satellites and other sensors.