What's a good time for a trip to Baja?

My girlfriend and I are planning a trip where we’ll stay with relatives in San Diego, then take a 3-day trip down the Baja to look for the good snorkeling.

GF says she’s heard that in Baja, even in mid-September, even the water is too damn hot. And immediately after that it’s the monsoon season and you won’t want to go near the place until after October. I say that by November, it’ll be too cold to do anything on the water in San Diego.

So is there no seasonal window where one could rely on decent weather throughout a region encompassing San Diego and a resort area in nearby Baja California where decent snorkeling might had?

This is not a particularly useful bit of information, but I’ve driven down to Cabo San Lucas in July 1991, and it was hotter than a motherfucker. I’m not sure when monsoon season is, but it never rained then. I would think that on the Pacific side, the water won’t be too hot for snorkeling, but on the Sea of Cortez, it wasn’t intolerably hot, but this was pretty close to Cabo. The snorkeling was great down there, but you obviously you aren’t going to make it that far south in 3 days. I doubt that the snorkeling is any good around San Felipe.

Here’s a site that shows some scuba sites on the Pacific side, where the water will be tolerably cool. I have no idea if there is decent snorkeling there, but I love the town of San Quintin. I think they may be building some humongous natural gas port there, so get there before they destroy it.

At least for the Southern end of Baja, the tourist season is from October to June. It’s never cold, it just goes from pleasant in the winter to hot and muggy in the summer. I’m not sure how that compares to the US-Mexico border region, though.