I would believe group A more
because, as we know "Precaution is always better an cure"
If I stay more cautious about it, there are less chances of the tsunami to cause a severe harm. If I don't stay much cautious, according to group B, and in case if their prediction goes wrong, I'll be in serious danger.
I chose group A because
even if the tsunami ain't powerful enough, I would be glad I was careful enough for it and it'll help me in future if I face another situation like this again
The consequences if I chose group B would be :
well, if I would have chose B, I won't have taken any Precautions at all
I won't have been careful enough
and in case their prediction went wrong, I would have to suffer high losses.
I hope it helps.... Have a great time ahead!