It rains a lot on the western side of the Southern Alps. Prevailing westerly winds pick up moisture from the Tasman Sea. The moisture-laden air tries to go up and over the mountains—which rise from sea-level to 12,000 feet in just a few miles. The air cools as it rises and cannot retain all the moisture, which falls as rain on the western slopes.
The Southern Alps truly define the weather on the South Island. From the tops of the Southern Alps down to the Tasman Sea is a rain forest, one of the wettest places on earth. East of the Southern Alps, the Canterbury Plain receives less rain than at home
Here are some rainfall amounts:
The chart above was in the Haast Visitor Centre on the west coast. The chart shows rainfall of 4.5 meters (180 inches) at Haast Pass and 6.5 meters (257 inches) at Milford Sound—similar to Doubtful Sound where we were yesterday. That’s a lot of rain! And we have been told that some spots high on the western slopes of the Southern Alps receive even more rain.Note the rainfall for Christchurch on the Canterbury Plain east of the mountains—26 inches. The average for Burlington is 33 inches.
Yet we were also told that while the West Coast of the South Island receives a lot of rain, they don’t have a lot of rainy days, except at this time of year. They say that winter is a nice time of year on the west coast. We were also told that the weather changes a lot, that it was common to have "six seasons in a day," but we did not see much variation in the weather.
Here is another interesting chart from the Franz Josef Glacier Visitor Centre farther north on the west coast:
I think we were there during a period of moderate, steady rain.I was surprised at the amount of agriculture on the west coast. In spite of the rain, we saw sheep farms, dairy farms, beef farms and deer farms, the same as on the eastern side of the mountains. Didn’t see any irrigation.
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