Looking at what is happening in the US as of right now, I'm fairly sure the second wave will be more like in July 2020. Unless you count it as still the first wave moving in from the coasts to the heartland and then as it moves back out is that the second wave?
Their analysis has new case rates falling off the peak as quickly as we arrived at it. And new case rates almost zero by end of June? This is wildly optimistic. Italy’s chart looks nothing like their forecast for the US.
It doesn't even have to be global, just a regional second wave in a tourist hot spot could crush tourism globally.