Notes on North Canterbury Wave Forecasts 

The time series of wave height, period and direction come from the NOAA WaveWatch 3 (NWW3) model. There is information about the model here. The data were extracted for the node off North Canterbury at 173.75 deg E 43 deg S, as shown in the map to the right.

The table below shows the statistics of the waves that occurred from 1-Mar-1997 to 31-Dec-2008.

At the top is a row of percentages with corresponding heights. These are the green dashed lines on the forecast. They are called percentage exceedance values. For 0.1% of the time, waves exceed 5.05 m in height. Conversely, for 99.9% of the time, waves are less than 5.05 m in height.

For 50% of the time, the waves are under 1.39 m in height. This means that if the forecast wave height is at or below the lowest green dashed line, the sea will be slight relative to the conditions that normally occur at this site. But if the forecast wave height is above this line, the sea will be rough, and if it is above the top dashed line, it will be extremely rough.

The body of the table shows the statistics of the direction of the waves. For 50% of the time (first column), the predominant wave direction is SSW, with 35% of waves coming from this direction. The remaining waves come from all directions, but very few of them come from the WSW to N (corresponding to offshore directions). As the wave heights increase, the SSW to S directions become more dominant. Notice that 12% of the largest waves come from the E.

Distribution (%) of the direction of waves over various heights.
Direction Top 50.0%
Hs > 1.39 m
Top 5.0%
Hs > 2.94 m
Top 1.0%
Hs > 3.94 m
Top 0.1%
Hs > 5.05 m
N 1.3% 0.1% 0.0% 0.0%
NNE 1.4% 0.0% 0.0% 0.0%
NE 2.4% 0.0% 0.0% 0.0%
ENE 7.2% 2.2% 0.9% 0.0%
E 9.6% 4.2% 2.7% 12.1%
ESE 7.2% 7.3% 4.4% 0.0%
SE 5.7% 5.5% 7.7% 0.0%
SSE 5.9% 7.5% 11.5% 6.1%
S 18.4% 20.8% 27.7% 33.3%
SSW 34.7% 51.5% 44.8% 48.5%
SW 1.5% 0.8% 0.3% 0.0%
WSW 0.4% 0.0% 0.0% 0.0%
W 1.2% 0.1% 0.0% 0.0%
WNW 1.4% 0.1% 0.0% 0.0%
NW 0.9% 0.0% 0.0% 0.0%
NNW 0.6% 0.1% 0.0% 0.0%