"Highest High Tide" is not a definition used by NOAA to describe tides. Is highest high tide referring to highest astronomical tide (HAT) or (Max tide) maximum observed tide or other?
I do not know; thanks for the heads up. There is an informational note in 555.1 that says to See NFPA 303-2011; perhaps that will be of some help. We (electrical code professionals) are expected to have a broad knowledge of so many things besides electrical...and I'm going to add National Oceanic and Atmospheric Administration to the list. Perhaps they are referring to a Proxigean Spring Tide?
If you have a suggestion to improve 555.2, I would implore you to please file a Public Input (PI), once the 2023 NEC code cycle opens up.
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