The level has dropped to almost exactly what it was in 1993, from a peak in 2008-9. It seems to be a combination of SOI dropping from its high in 2009-10, a drop in sea temperature from 2008, and a rise in barometric pressure after 2011. A change of 1 hPa (=millibar) results in a change of 1cm in sea-level. Higher pressure, lower sea-level, and vice-versa. "Storm-surge" is due to low pressure (and high onshore winds) in a storm system. This is SOI to November 2016:
I'm checking on nearby (well, relatively) stations to see if there's anything remotely similar. I've already checked CGPS station data; here's that for Port Vila; the tide gauge is about 1 km away at the Cruise-ship port.
Although the red velocity analysis on the left says "Not robust", there's little change. More later maybe.