The meaning of "have a blast" is:
The definition of "have a blast" is:
(verb) have a great time
Have fun on your vacation, I hope you have a blast.
A: How was your class?
B: I had a blast! My teacher, Mike, is so great!
I am having a blast here in Canada. I hope to see you soon!
From the Blogs:
Angels Have a Blast Against Yankees