Wow, that's some storm:
I would not wait for the winds to start increasing;when a cloud formation looks that ominous,
I get ashore and stop as soon as I see it, no worries about getting back upwind, having a few boost, or whatever.
Don't know but it looks like this kind of formation could give a catabatic-like effect, when it hits it could be 2-3x as much as you otherwise expect...
From the picture it looks like all kites should have been down 10-15 minutes ago.
One last tack or boost could be all it takes to use up the "safety" margin before storm winds, and there is no way to tell how far in front of the cloud the winds will reach.
The speed of these things can be deceptive! Careful....
Glad no bad injuries!