Longer term wave climatology is used to predict the statistical chance that for instance a given wave-sensitive ofshore operation - such as lifting a major topside element into place - will be delayed by sea conditions which are too rough. Sets of characteristic wave data values can be grouped and arranged in a table such as that given below for all wave directions in the winter season in areas 8, 9, 15 and 16 of the North Atlantic Ocean. A ”storm” here is an arbitrary time period - often of 3 or 6 hours - for which a single pair of values has been collected. The number in each cell of this table indicates the chance that a significant wave height is between the values in the left column and in the range of wave periods listed at the top of the table.