I've also done that a few times at night (Actually to Cat I.). Even though there is no shelter, the bank helps moderate the seas. The times I've anchored out on the bank, the problem has been not so much sea state, but tidal currents swinging the boat somewhat sideways to the prevailing wind
and waves, making things a bit rolly. This of course will change as the tides change and depend on the sea state.
My experience about a lane of traffic and getting out of it to anchor echos those stated in above posts.