IM NZ 2021 Forecast

The weather for IMNZ on Saturday is looking promising, if not necessarily super fast. I suspect the limited daylight hours will cause more consternation than the environmental conditions.


windy.com shows the predicted wind direction and strength

You're going to have a fairly direct headwind all the way out to Reporoa. But it's not particularly strong. While you're battling into that wind - console yourself with the thought that this is the fastest wind direction as it pushes you back up to the racecourse. A southwester (instead of this northeaster) is the slowest wind direction as it adds resistance to the overall uphill leg back to Taupo.

As a quick reminder of how to read this image (because I keep getting asked). You are sitting in the middle facing towards 0 degrees. The distance of the graph line from the centre shows the proportion of time that you will have wind from that direction. 

What this shows is that you will either have headwind or tailwind - not much of anything else. 


The forecast is for cloud cover, with a very low chance of rain (2%). Temperatures are good for this time of year - 14 deg at 9am (most people will be getting on the bike from 9am onwards). Not so flash for 70.3 athletes as it will be 12deg when you finish the swim.

Atmospheric pressure is moderate compared to other editions of the race so air density overall fairly similar to last year.

Inpact on Performance

Bike SplitDisadvantage compared to 2020

So it's a little slower than last year based on the forecast. 

That shouldn't stop you from being able to set a PB if you've managed to maintain form and motivation after the postponement.

Water Conditions

Currently the outflow from the Lake is at a slightly higher level than last year (209cumecs compared to 182) so you should find more of a boost on the return leg and into the Marina.

The lake level is 30cm lower than last year, but I can't think of any way that would have an impact. Maybe it will be easier to see the golf balls?

The lake is warm at around 18.5deg, but I can't find old data to compare.

It should be quite a fast swim


I've analysed days with this wind direction previously and found that riders taking over 6 hrs were heavily penalised by poor pacing. The times at the front of the field usually track extremely well with the predictions, but the risk for athletes not at the pointy end is getting overexcited fighting the headwind on the way out, then getting penalised for the rest of the day.

Curbing your desire to hit a certain speed on the way out will help a lot for your day overall.

The Race

On the mens side - the abscence of international athletes is unlikely to impact the times achieved. We have a lot of depth in NZ. The established contenders will be watching for the effect of Kyle Smith in his first IM outing (he has been working hard on optimisation) and Cameron Brown will look to be at least half an hour faster than the next nearly 50 year old again.

The pro womens field offers strong athletes but a notable lack of depth with only four athletes. Dr Hannah Wells makes her debut at IMNZ so will be looking to make a splash.


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