St. Augustine does not have a class A inlet. If one wants to avoid Matanzas with frequent shoaling, it is adviseable to go out the St. John's River and not try to go out St. Augustine. This picture shows the inlet entrance from the ICW when there was an onshore wind. There is surf all across the inlet, which is not a nice situation to be in with a boat.
Coming into St. Augustine from the north by boat, the main caveat is to avoid the big shifting shoal on the west side of the channel. It sticks out way beyond the mouth of the river into the inlet so you have to go almost out the inlet before you can turn and go toward town.
The way that this shoal is marked is with pilings with signs on them that say "Danger", but also the channel markers are red floating buoys which are moved around as necessary to allow boats to clear the shoal. These markers are really small though, and easy to miss.
The picture shows one of the little floating red buoys looking through the boat lifelines towards the lighthouse. One of the Danger signs is on the extreme right edge of the picture.