We had exactly those conditions a few years ago.
A double wave from the Sun. The first was slower and we saw coming over the course of 1-2 days.
The second was unexpected and followed the course of the first, as it had cleared the path of any particles that would slow it.
It missed the Earth, on the plane of the Earth's orbit. Had the event happened two weeks later, on the same trajectory it would have been a direct hit with minimal warning. 
I periodically look at the solar weather tracking:
http://sidc.be

Interesting reading.