I don't know that anyone can reliably forecast what the world's...

I don't know that anyone can reliably forecast what the world's going to do to Coal prices from one year to another.
And because the world has decided that Coal will have no value going forward (well, that's the plan) it's important that results in the form of dividends are constant and higher than average to cater for that moment in time when Coal, and therefore, NHC prices, are worth next to nothing.
Their production increases across the next few years should support their results if coal prices drop too much.
This is not a stock to put away in the bottom drawer (as they say in the classics) but needs to be watched carefully on an almost daily basis.
With that in mind, I read through the following link regularly.

Coal - Price - Chart - Historical Data - News (tradingeconomics.com)

This helps me a little. Each of the tabs here is worth checking. Their forecasts haven't always been totally accurate but it's a start.