We could always take the TNG approach to the groundhog day concept...
The day starts off like it normally does every day however at the end of the day there's a catastrophe and since we're in a loop it restarts itself.
The next day people either have a sense of Deja Vu with a few people remembering the entire event. The people who remember try to convince others to stop the catastrophe and with the catastrophe happening at the same time.
People who are off the island (Alumni or people traveling) can get the idea that something is wrong when someone from the island calls them on the same day and don't remember the day before etc. etc. etc.
And when everyone figures out what the catastrophe is and stops it from happening the time flow returns to normal.
Re: More specific!
The day starts off like it normally does every day however at the end of the day there's a catastrophe and since we're in a loop it restarts itself.
The next day people either have a sense of Deja Vu with a few people remembering the entire event. The people who remember try to convince others to stop the catastrophe and with the catastrophe happening at the same time.
People who are off the island (Alumni or people traveling) can get the idea that something is wrong when someone from the island calls them on the same day and don't remember the day before etc. etc. etc.
And when everyone figures out what the catastrophe is and stops it from happening the time flow returns to normal.