A multi-faith prayer and release of doves is due to take place at 09:15 BST.
Organisers are encouraging attendees to wear or accessorise in "green for Grenfell" in a display of "reverence and respect amidst the revelry".
A "ring of care" will be formed around the tower by police.
More than 80 people are believed to have died when fire engulfed the Grenfell Tower block of flats on 14 June. The carnival route passes near the tower.
Pepe Francis, chairman of the carnival trust, said: "We support the suggestions of the local community and wider carnival community to start this year's carnival earlier.
"This will be the first opportunity for visitors to carnival to pay their respects for those affected by Grenfell."
Hundreds of hand-drawn tributes, flowers and candles will be protected by fencing, while the public have been asked not to take selfies at the site.
A reflection zone will be placed near the burnt high-rise, where performers will lower the volume of their music.
MP Emma Dent Coad, who likened the carnival to a wake, will give a speech ahead of the dove release.
At 15:00 on both days, hundreds of thousands of revellers along the route are expected to pause and observe a minute's silence to mark the tragedy.
A spokesman for Grenfell United, a residents and survivors group, said: "We hope people will follow these requests from us and our friends and family in the wider community.
"They will enable people to pay their respects; be conscious of our vulnerability; and show solidarity for our ongoing demands for housing and full justice, in the creative spirit of carnival."
Steel barriers, concrete blocks and a ban on vehicles will be in place to protect revellers from the threat of terrorism.
Scotland Yard said there was no specific intelligence but security plans had been "thoroughly reviewed" after the Barcelona attack.
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