Just trying to think critically. What is the theory that could link the Qposts about "WATCH(ing) the water" from 3 years ago to something that's so complicated and hard to predict reliably as weather events past a couple days today?
Weather predictions are made on simulations based on "the current weather" and "past years weather data", introducing a bias making it less likely to predict such a storm of catastrophic events.
Not entirely sure what your asking but i'll brainstorm here anyway, what if "watch the water" IS referring to the INSANE floods that have happened in the last week.
Theoretically you can predict the weather for the rest of earths existence if you had every point of data and understood all the science, it would just take a super computer the correct precise data entry and the right algorithm.
I don't think the human race is at that point because weather as you mentioned is one of the most chaotic systems we know of, you'd have to include every square millimeter of the earths content and assign it's current heat, heat transference rates ect. all they way up to solar activity and astrological anomalies, think asteroid hits, radiation blasts ect.
All that aside, it would be much easier to predict massive flooding, this would only require the data for the water cycle, and we understand the science of this very well.
And aside from that you could just monitor Dam conditions and predict a failure, and maybe help prevent the required maintenance once you do see an issue to get a rough date of WHEN the dam will fail.
Another way you could predict mass floods is if the enemy was planning to use WEATHER WEAPONS to induce heavy rainfall and floods, you could figure out what the enemy needs to trigger their "flood plan". then all you would need to do is scare you're enemy into activating that plan around the time you wanted it to happen.
Where you say it's a bias because you're using the current weather is kind of inaccurate it's not so much a bias as it is a lack of monitoring and collecting data meaning it's a best guess, (nit picking but hope you get my point) something the military would be able to do with much better precision than anything civilian.
Now to address your first question about watching the water" no one has any concrete idea what this is actually referring to and most likely is referring to multiple things it's actually not a common theory that it relates to weather at all, but with all the FLOOD COMING / WATCH THE WATER talk surrounding declas it would be accurate to associate it to the floods we are seeing now if we really are about to get the data dump we've been waiting for tomorrow. (McAfees Deadmans Switch)
Some would just say that they are time travelers so just need to check the "flood history from the future" and that's how they could predict the massive flooding xD