The Touryst

Arrive at Hawayy Island
Get shorts from Balloon Salesman (between Shirt and Ice Cream shops)
Change into shorts in changing stations next to announcer tower
Talk to announcer and surfers to start contest

You can retry as much as you can, 10,000 points completes the to-do list objective. Build up speed by doing tricks and get the height I achieve in the video link below. The height still took me around 20 retries to finally get and its probably better to do more than just the two tricks over and over to get that height but this is how I did it.
Nailing your drop ins is also a must

Updated clip to be playable without leaving page

You don't have to do any special or certain amount of tricks. You gain speed and height by staying as close to the top of the wave as possible - when you jump out of the water, turn and land, then turn back up to get out of the water as fast as you can - rinse and repeat

All credits go to michael el loco

I put this as a guide there. His method was drowned among too many comments on another guide & fortunatly it works like a charm.

I did it first try after following his advice

On Hawayy Island, you can join a surfing competition; however, first you need to buy some shorts. These can be purchased from Enzo, just outside the Tshirt shop. Change into them in the beach changing room and then join the competition. You can surf as many times as you want. To do a 540 degree turn, you need to build up your speed meter by doing small tricks. With enough speed, you will start to jump higher making it possible to complete larger tricks.

Here is a video guide with English commentary!

Guides here said we need to wait for the RED speed to do the trick, but I failed since the wave would come faster than I got to the red.

I tried to it on orange speed with a little bit of luck on getting the require height.

Here the video:

Once you don't need to chase for the red speed, all you need to do is make the correct angle to get the height.

This is done on Hawayy Island, and you can buy the Guide from Leysure Island. When you get there you talk to the ref on the stand, will then need shorts. Buy them from the vender between the ice cream man and the t-shirt store, then you can compete.

As for the surfing itself, you just need to get enough speed to get the 540 degree turn. You get speed by going up, then coming down the wave. You don't actually need to catch air to build speed, but I've noticed you get higher after going straight up the attempt before. So if you get to about 90% speed, then go straight up and do a 360, then come down and go back up, you usually have enough speed to get the 540. I was able to get it three times in a row after trying that, but it took me 27 attempts up to that point lol. You do have a set amount of time before the wave catches up to you and stops your run, so try it to get a feel for it, and then you should get it. Hope this helps, video below showing how to build speed easy.

The controls are not at all intuitive. After reading many guides and a LOT of playing, I discovered you should only move the controller to right the board toward the top then push to the right to orient the board for a good landing. Nothing else. Keep your finger off the stick if you aren’t redirecting up or for a landing. Anything else will cause a crash.