I wrote a response about the plague of frogs a while ago that sort of answers this. Greta Hort is probably the biggest 'natural' sequence proponent but as I've pointed out, there are problems with this (and that's only dealing with a few plagues). I highly doubt the plagues are meant to be natural neither would the writers conceive of them as being natural either, this was very clearly Yahweh's hand at work.

I've crossposted this to /r/AskBibleScholars. Here's the direct link.