4 year la Nina is a big surprise, but a 4 year la Nina given we've had 3 years already is a much smaller surprise

That’s not how probabilities work.

If I flip a coin and get heads 3 times in a row it doesn’t change the odds on the 4th flip.

It is how probabilities work. A plain example: The odds of flipping ten heads in a row are 1/1024, but if you've already flipped nine heads, the odds of flipping ten heads are 1/2.

Can you please tell me in detail how you're not agreeing with what I said? I said the exact same thing.

"If I flip a coin and get heads 3 times in a row it doesn’t change the odds on the 4th flip."

It's not the odds of the fourth flip, it's the difference between four flips and a fourth flip.

Look upstream, you'll find someone (you perhaps? I don't care who) who doesn't realise whether the current La Niña situation is equivalent to a fourth-flip or a four-flips situation. A common problem in statistics, in my experience: People sort of understand two statistical statements, but then apply the wrong one to the real-world situation they're in.