Does Tempestuous Magic allow you to avoid attacks of opportunity *after* they have already triggered?

Question

My level 4 storm sorcerer has the shield spell. Imagine I am within melee range of three enemies. I move out of reach of all three provoking three Attacks of Opportunity (AoO). The first attack hits but I use my reaction to cast shield to avoid it. Using my bonus action, I use Tempestuous Magic immediately after casting Shield to fly 10ft away.

Would this:

a) Allow me to avoid the last two AoO because TM prevents you from provoking AoO or would that not apply because the previous two AoO have already been triggered/"provoked?"

Tempestuous Magic

Starting at 1st level, you can use a bonus action on your turn to cause whirling gusts of elemental air to briefly surround you, immediately before or after you cast a spell of 1st level or higher. Doing so allows you to fly up to 10 feet without provoking opportunity attacks.

b) Allow me to avoid the last two AoO because by flying 10ft away I am no longer a valid target for the remaining two AoO or would the attacks still happen because of the following?

To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach.

c) Something else entirely.

If you are wondering why not just cast a 1st level spell before moving and fly away without provoking AoO I can think of some reasons. Imagine you either don't have misty step or are out of lvl 2 spell slots. If I think (or know) the enemies will catch up on the next turn this would be the most optimal way to utilize my 1st lvl spell slots to keep me alive (if it works how I hope it does)

Answer 1

You cannot use a bonus action while reactions are being resolved

If you move away, provoking 3 AoO, those three creatures all use their reactions to make those attacks, before you leave their reach. During this time you can go ahead and cast shield, as that's a reaction which has a trigger that can be activated whenever you are attack. However what you cannot do is use a bonus action (or a normal action or your movement or your free objection or whatever else), in your case the TM, until those triggers have been fully resolved. This is explained in the last sentence under the reaction segment in the PHB:

If the reaction interrupts another creature’s turn, that creature can continue its turn right after the reaction.

This tells us that a reaction is something that interupts a turn, and leaves the creature's whose turn it would normally be unable to act until the interuption has passed. The only thing that can interupt a reaction, is another reaction. Again in your case shield, another commen case is counterspelling a Counterspell or another reaction spell.

This means that right after those 3 attacks have been resolved, you can go ahead and use TM (given that you cast shield during that time), though of course then it would not be of any use to you in this case. I know this slightly contradicts the wording of TM "you can use a bonus action [...] immediately before or after you cast a spell" and one might argue that 'specific beats general' applies in this case, but I would personally argue against it, as I would wager that the designers did not fully consider this interacting with reaction spells on your own turn. Meaning that immediately in this case means, as soon as you are able to cast bonus actions again, which is after the resolution of any and all reactions.

You could still prevent those attacks by moving cleverly

If you are indeed surrounded by 3 different attackers, you might be able to use your movement in a thoughful way, as to only provoke one attack at a time, and then be able to prevent the other two with TM. E.g. if the enemies are to your south, southwest and southeast, you could instead of moving north and provoking all three attacks, only move west or east, moving only out of the range of one enemy and thus provoking only one attack. Then you could cast shield as intended and then use TM after the attack as a bonus action, preventing the other two attacks.

Answer 2

RAW, probably

Contrary to TreeSpawned's logic, the statement

If the reaction interrupts another creature’s turn, that creature can continue its turn right after the reaction.

does not imply that a Reaction "leaves" a turn, only that it instantaneously "interrupts" a turn.

It's definitely still the PC's turn when the opponents' Reaction take place, so the PC can use a Bonus Action.

You choose when to take a bonus action during your turn...

The question becomes a matter of the order of resolution of events.

The PC's Shield Reaction interrupts the opponents' OA Reaction. Casting Shield interrupts the interruption, so it resolves first. Since TM allows the PC to fly immediately before casting the spell, all attacks might be avoided.

Practically...

I believe a reasonable GM should let the PC avoid most, if not all, of the attacks. But, that's an opinion.

Turns are an abstraction of time, and the break down "unrealistically" when you try to atomize the events in them, like casting spells. Talk to your GM. The best solution may be to roll some dice to determine, probabilistically, which opponents' attacks resolve simultaneously and which ones attack moments after the TM takes effect.