Simple answer is English has no future tense as such. I teach English as a Second Language and the standard explanation is it’s dependent on factors such as certainty of knowledge and who shares that knowledge.
So ‘The train arrives at the station every day’.
‘I expect the train will arrive in the next five minutes’.
‘I know the train is going to arrive soon because the signal has just changed’.
‘The train will be arriving at 18.02 at Platform 5 according to the timetable’.
It’s a great job, and always open to interpretation!