Mean Higher High Water comes from taking the taller of each tidal day's high waters and averaging those heights across the tidal datum epoch. It marks the top of the normal daily tide range and serves as the base for inundation mapping, coastal flood thresholds and many wetland and sea level rise studies. Flood forecasts often quote water levels as feet above MHHW, a handy proxy for water depth on the lowest shoreline ground.
Gauge peaked at 2.4 feet above MHHW, that's minor flooding on the waterfront streets.
Also heard as
- mean higher high water
Related terms
MLLW
Mean Lower Low Water: the average height of the lower of each day's two low waters, used as chart datum in the United States.
MHW
Mean High Water: the mean height of every high tide across the datum epoch, often the line that defines the legal shoreline.
High tide flooding
Shallow coastal flooding that happens when ordinary high tides exceed a local flood threshold, often without a storm.
Tidal datum
A local zero for heights, computed by averaging one stage of the tide, such as high or low water, across many years.
Storm tide
The full water level reached in a storm: astronomical tide and storm surge added together.