I would not say "unexpected". See the third line:
"Pay no mind to the distant thunder"
That means the storm is coming, he should have foreseen it, but instead, he just is too focused in another things:
"Beauty fills his head with wonder, boy..."
It's liek some guy who has a good time, and thinks that nothing can go wrong, but because of this optimism he fails to see the signs that something bad is going to happen, so he is unprepared.
I would not say "unexpected". See the third line: "Pay no mind to the distant thunder" That means the storm is coming, he should have foreseen it, but instead, he just is too focused in another things: "Beauty fills his head with wonder, boy..." It's liek some guy who has a good time, and thinks that nothing can go wrong, but because of this optimism he fails to see the signs that something bad is going to happen, so he is unprepared.