I'm also in a microclimate. Zone 9b / 10 just like you, while areas only 25 miles north and west are 8a / b. when cold fronts pass through, the wind has to pass over lake pontchatrain, which is really a large tidal bay, thus warming the air.
We had one night that dropped below 30 and a couple light frosts.
One thing that I never knew was that latitude 30 during the summer, recieves more solar radiation (or insolation) than any other latitude, including the equator. The Amazonian plants we all love so much grow like crazy here during the spring, summer and fall, and seem to weather the winter just fine. They may loose they're leaves or go dormant, but our winter generally don't kill them. My caapi has endured freezing temps with no ill effects and my mimosa hostilis can take frost and stay green, although the one night in the 20s did fry it's leaves, but I'm sure they'll come back. Hbwr can also take freezing temps and stay alive.