For the maximum high tide (the highest possible high tide) to occur at a place, several conditions need to line up at the same time:

  1. Sun, Moon, and Earth in a line (syzygy)
    • This happens at new moon and full moon.
    • Their gravitational pulls reinforce each other, producing spring tides , which have the greatest tidal range (highest highs and lowest lows).
  1. Moon at or near perigee (closest to Earth)
    • When the Moon is closer, its gravitational pull on Earth’s oceans is stronger.
    • If a new or full moon happens near perigee, you get perigean spring tides , which are among the highest high tides experienced routinely.
  1. Favourable coastline and seabed shape (local geography)
    • Narrow bays, funnel‑shaped estuaries, or wide continental shelves can amplify the incoming tidal wave.
    • This is why places like the Bay of Fundy reach extreme tidal ranges, with mean ranges over 11 m and extremes up to about 17 m.
  1. Resonance with the natural period of the basin
    • If the natural oscillation period of a bay or gulf is close to the tidal forcing period, the water can “slosh” in resonance and increase the maximum high tide height.
  1. Favourable weather conditions (for truly extreme water levels)
    • Low atmospheric pressure slightly raises sea level.
    • Strong onshore winds can pile water against the coast, further elevating the high tide above the purely astronomical prediction.
    • These factors can make the observed maximum high tide higher than predicted and can contribute to flooding.

So, in essence:

The largest possible high tide at a given location occurs when a perigean spring tide coincides with local geographic amplification and, for truly extreme events, supportive weather conditions like low pressure and strong onshore winds.

Mini recap

  • Alignment of Sun and Moon → spring tide (biggest tidal range).
  • Moon closest to Earth → perigean effect (stronger pull).
  • Funnel‑shaped coasts or resonant bays → extra amplification.
  • Low pressure + onshore winds → push the maximum even higher.

Information gathered from public forums or data available on the internet and portrayed here.