After having read most posts, I recall a similar incident I experienced in an A340 ca. 20 years ago in ... GRU... right next door to VCP.
Our problem then, was that the aircraft was - in hindsight - obviously overweight and a varying light wind was not helping either.
OAT was reported as being 36C - which resulted in a TOGA take-off.
Initial acceleration was normal (i.e. the aircraft started moving), but just after(!!) V1 the IAS acceleration arrow went from 5 knots up, to 3 knots down, 5 knots up etc. and a veeeeerrrry slow further increase in speed.
Thrust levers were at their physical forward detent, A/C on APU and WTF-grunts where heard as we lumbered down the runway and tried to figure what to do.
And then, as the centerline lights turned from white to read-white the "old man" flying ever so gently pulled on the stick, got it flying in ground effect, but kept the very gentle rotation going as the speed increased, and when we were sure it was actually flying, we raised the gear lever.
Behind RWY 07 (?) there was a large white warehouse that produced an updraft that helped us over the hills to the East.
Next time around I told the local mech about our experience and he said. "Everybody knows, you have to had 3-4 degrees to the reported OAT when calculating the T/O performance in this heat."