5. The modal will + be + -ing form
Progressive forms usually refer to a situation that began before a time point continues through and after that time point, and into the future, and is of limited duration. The combination of this idea with the modal will, expressing certainty, leads to the modal will + be + -ing form referring to a situation beginning before a future time point and continuing through that time point:
Sally’s plane takes off from Heathrow at 9 o’clock tomorrow, so by about midday she will be flying over Istanbul.
It is also possible that the speaker is more concerned with the pure certainty of the action happening than with volitional aspect that might be implied by the use of WILL by itself:
Emma will be seeing Luke tomorrow.
Some writers claim, with some justification, that this use of modal will + a progressive implies, by its lack of reference to intention, volition or arrangement, a 'casual' future. Depending on the context and co-text, the speaker may be intending a ‘casual’ futurity, or may be indicating a situation in progress at a particular time.
from: Ways of Expressing the Future in English
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