Winds & Storms

Winds & Storms

Looking back at the Wahine Storm

Historical records of pressures, winds and waves have been collected for Cyclone Giselle, more widely know as the Wahine storm, after the Inter-island ferry TEV Wahine that sank off Wellington Heads with the tragic loss of 54 lives. The storm on 9 to 10 April 1968 caused winds of up to 150 km per hour at Wellington Airport and high seas and storm tides occurred along the east and south coasts of the North Island as the storm tracked south. Most pundits suggest that the Wahine storm was the second biggest storm to strike New Zealand last century, second only to the storm of the 2nd of February 1936 in terms of coastal damage. (Note: storms were only assigned names from 1963 onwards).

There were few measurements available for the 1936 event, so the 1968 Wahine storm has been reconstructed using a computer model to simulate winds and pressures based on a re-analysed NCEP global wind model. Then the regional winds were used to drive a wave model to obtain a picture of what the deep-water wave heights may have been along the east coast of the North Island. Snapshots of the preliminary wave model results are shown in the two diagrams at different stages of the storm:

Predicted significant wave height at 1600 hrs on 09 April 1968 as Cyclone Giselle passed through the Bay of Plenty. The arrows indicate the average wind speed and direction.

Predicted significant wave height at 0900 hrs on 10 April 1968 as Cyclone Giselle passed east of New Zealand.

Hindcasting such large storms provides a way of testing the forecasting skill of modern wind and wave models and at the same time provides valuable “data” to fill in the gaps of 1968 observations. This data is useful input into coastal engineering design for ports and coastal structures to better withstand such extreme storms in the future.