Forecasting is a bit of hit and miss but many major storms are forecast and typhoons/hurricanes tracked which has saved countless lives in the process.
I don't trust metservice further than I can throw them. Weatherwatch is generally more accurate.
Now the science of it is apparently quite involved but in essence, forecasters monitor weather fronts, low pressure and high pressure to determine what our weather is going to do. Humidity, sea temperatures, wind speed/direction and pressure (plus a few other entities) makes predictions pretty accurate for the experienced climatologist. That said, they do get it wrong from time to time.
Last weeks storm that hit down south was predicted by Weatherwatch a week before it hit. NIWA said its a waste of time, storm in a tea cup blah blah. 3 days later metservice and NIWA changed their mind and agreed with Weatherwatch. Bit of a pissing contest going on between them at the moment.
yr.no and a few others are accurate but I would be more inclined to go with a local weather guy and on top of that, the rural site gives more info like fog and snow.
I am not a climatologist but just enjoy the citizen science side of it.
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