These guys are not predicting the weather per say...The sun is not going to cool..
This is a cyclical orbital mechanics observation that they have identified will likely affect us in 2030.
It has everything to do with what hemisphere of the sun (it rotates) will be facing us at we orbit it.
What they are saying is that the cycles will cancel each other out and the side of the sun we will be facing will be very calm and docile for a number of years...The Maunder Minimum.
I would try to explain this further but it’s way over my pay grade as to the mathematics..
Valentina Zharkova is a Professor in Mathematics at Northumbria University. She has a BSc/MSc in Applied Mathematics and Astronomy, a Ph.D. in Astrophysics, certificate in project management.
https://www.northumbria.ac.uk/about-us/our-staff/z/professor-valentina-zharkova/