How severe wave conditions are possible on the Norwegian Continental Shelf?

The paper describes results from experimental runs with a version of the WAM Cycle 4 computer model, run operationally at the Norwegian Meteorological Institute. The question to answer is how high waves may become in weather conditions that are extreme, but plausible in a meteorological sense. Results focus on 2 sites: the Northern North Sea under southerly wind conditions and Haltenbanken under southwesterly conditions. For the North Sea site, the selected approach was to reduce the low pressure over UK in a severe southerly condition and intensify the high pressure over Scandinavia/Northern Europe. For Haltenbanken, experiments were run with deepened low pressure and changing speed of propagation of the low. The study shows that the worst scenarios can produce significant wave heights of a severity being comparable to sea states being predicted as 10−4 probability events1 by traditional methods based on observed sea states. Minimum and maximum pressures used in the worsening scenarios for the lows and highs were never deeper or stronger than observed during the 20th century, but the simultaneous occurrence utilized herein for the extreme highs and lows are not observed. An assessment of the annual probability of the simultaneous occurrence is presently ongoing.