Only one Category 5 hurricane has ever made landfall on the island of Puerto Rico, an unincorporated territory of the United States. That was the 1928 Okeechobee hurricane that crossed the island with sustained winds of 160mph and caused more than 300 deaths on the island. Later, that storm would become the second-deadliest hurricane in the history of the continental United States, with 2,500 deaths in Florida.
Now, Hurricane Maria seems likely to become the second Category 5 to hit Puerto Rico. As of 5pm ET, the storm is intensifying, with 165mph sustained winds. Critically, the storm's central pressure is also falling, and it is down to 916 millibars as of Tuesday evening. At that central pressure, Maria would rank among the 10 most-intense landfalling hurricanes in the Atlantic basin in the last 150 years.
In response to the threat to the US Virgin Islands and Puerto Rico, warnings from the National Hurricane Center have become increasingly dire during the last 48 hours. In a Tuesday evening public advisory, forecasters warned of Maria's "potentially catastrophic" winds, rainfall, and storm surge. They urged that final preparations be rushed to completion.