How weather-related tides affect forecasts of storm surge

Wednesday 20 June 2018 - 14:00 to 15:00
NOC Liverpool - Nicholson Lecture Theatre (University of Liverpool).
Dr Joanne Williams (NOC)

Tide predictions based on tide-gauge observations are not just the astronomical tides, they also contain radiational tides - periodic sea level changes due to atmospheric conditions and solar forcing.
This poses a problem of double-counting for operational forecasts of total water level during storm surges. In the UK forecast, a regional model is run as tide-only, with astronomic forcing alone; and tide-and-surge, forced additionally by surface winds and pressure. The surge residual is defined to be the difference between these configurations and is added to the local harmonic predictions from gauges.
In this talk I'll show how we used the Global Tide and Surge Model based on Delft-FM to quantify the weather-related tides that may be double-counted in operational forecasts. I'll show that the global S2 atmospheric tide is captured by the tide-surge model, and changes in other key constituents, including M2. I'll also talk about the extent to which the "Highest Astronomical Tide", which is derived from tide predictions based on observations, may contain weather-related components.

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