How fast is fast?

At home in Alberta, we see heavy rainfall warnings if there's an inch or more in the forecast. Streams generally are out several days with that amount. If we get 50mm (2"), the water's typically out 5 or 6 days. It took some time to get used to, but when we first started seeing warnings of 150 mm in a day here in NZ, we were amazed at how unfazed fishermen are. Then we started to see 200, then 300, and up to 450 mm of rain in a one day forecast. And people anticipate fishing soon after. How soon? How fast do rivers here, particularly in the alps or west coast, come down? How fast is fast? Check out this flow chart:

Imagine getting used to a river going from 40 m3sec to over 400, and fishing it the next afternoon! The country is rock that funnels the water off and back out to sea. The rain forest on the coast absorbs what it can, the rest simply flushes. It takes some time to get used to, but if you learn to play the game with the flows, it can be quite good.
And tied in to how fast is fast, typically if there is a big rain front on the west to central island, the east side is dry, warm, and windy as hell. Today the west is forecast to get 3 - 400mm of rain and where we are the wind warning is sustained 120kmh. The tops are seeing 140 kmh. The interesting part of that wind, being the leading edge of the front, is that at 5 am it was +24C. Neat stuff.