Please note that due to unusually high temperatures at the moment, for safety reasons, the townhall of St Gervais and the Prefecture of Haute-Savoie say that the ascent to the Mont Blanc by the voie normal is strongly discouraged. The dangerousness of the Couloir du Gouter is the main reason for that warning. If people insist on going they remind them that they should very early and come back before the temperatures reach their peak of the day.
For information, the mountain guides associations of Chamonix and Val Montjoie have suspended (for now) their climbs to the summit via this route.
If the situation does not improve, authorities may shut the access to the Gouter mountain hut (they did that twice in the past during the summer of 2015).
This is info taken from a French newspaper and published on the 22nd.
Hopefully the situation will improve when you go there so that you can enjoy a nice climb and activation.