Experts say Irma is now so powerful it is registering on devices designed to detect earthquakes. Scientists picked up the background noise of winds causing trees to move and crashing ocean waves on their earthquake-detecting seismometers. It is expected to become the second powerful storm to thrash the U.S. mainland in as many weeks after devastating Hurricane Harvey. A mandatory evacuation is under way in the Florida Keys. In addition to Irma, Tropical Storm Jose has now formed behind it in the open Atlantic and is expected to develop into a hurricane. A third tropical storm – Katia – has also formed in the Gulf of Mexico with winds but is expected to stay offshore until Friday morning.