[onnoonno]

I see, thanks. But that rather sounds like the buoy itself is switching modes?

From the look of all the plots, even the far-away ones, it rather looks to me like they have been remotely switched into event mode (with that 15s stuff being plotted at about the same time)?

I guess I am really confused about the time stamps.

[adanto6840]

Based on this page, linked by someone just above, it sounds like they do have 2-way comms (Iridium) and can remotely be put into 'Event Mode'.

http://www.ndbc.noaa.gov/dart/dart.shtml

I think it's a combo of noise when that was activated (see the page above, describes exactly what it reports when it goes into that mode, etc) -- and then for the one that shows a substantial sea level rise, it's likely just the pressure since it's all pressure-based sea-level measurement "estimates". Guess I kind of thought it measured actual rise/fall of the buoy, or maybe used GPS or something, but makes a bit more sense that it's solely based on sea-floor pressure.