Storm surge is the response of the ocean to changing atmospheric pressure and wind.
Storm surge displaces sea level from the tide.
For negative storm surge, sea level is displaced below the tide (e.g., up to 05 May);
For positive storm surge, sea level is elevated above the tide (e.g., after 05 May).
The high-frequency oscillations in sea level are the FIG waves.
They are particularly noticeable at high and low tide when sea level is relatively flat,
but they occur throughout the record and they do not change with tide.