I live in Mississippi and I was really curious to find out how disasters would play into landlord/tenant law. I spoke with a few lawyer buddies and this is the impression I get:
If there was no electricity, unsafe water, etc, the unit was uninhabitable during that time. Your tenant would have a solid case for not owing rent for just those 2 weeks, but it was their choice to stay gone for the whole month. That being said, there is no doctine for "in the event of a natural disaster" so if you think you can win an eviction for these reasons, go ahead and try. It's really about what you can work out with your tenant. If the unit was partially destroyed then technically they could live somewhere else and not owe rent until it was repaired. Lower his rent to account for the 2 weeks without power, but after the power was restored, it was the tenant's choice to remain out of town, and you deserve rent for the other 2 weeks.
I could be wrong, but this is the way things were explained to me. I hope either this helps, or someone else here can correct me.