It was raining, yes, but it was not a TS or +RA, more like a -RA or DZ for the past days
Firstly, my deep and sincere commiserations to all those involved in this incident.
I departed Sao Paulo (GRU) the evening before this incident, and I would assess the rainfall that was falling most of Monday as moderate and occasionally bordering of heavy - I got quite wet doing the walkround!
Now I am not commenting on the cause of the incident, but I can confirm that the landings on the Monday were to the south as seen from crew hotel, so the aircraft would have been depositing rubber at the northerly end of the runway.
I have personal experience on landing on newly resurfaced runways (LHR etc) prior to grooving and can confirm that the stopping characteristics are much poorer than normal, and can easily equate to those experienced on contaminated runways.
[Trying to be factual]