Sunday’s downpour deters some festivalgoers but Monday is expected to be busier, with police remaining on alert

Like in a secret lair from a James Bond film, a phalanx of video screens hangs from walls piping in streams of pictures. At its head is someone set on, if not domination, then on avoiding the loss of control: commander David Musker, in charge of the Metropolitan police’s operation at Notting Hill carnival.

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The bank of 18 screens in his personal command suite mostly shows bedraggled crowds who have braved a day-long downpour.

But Musker says the rain does not mean police can ease off. “The most violent carnival we had was five years ago when it poured,” he says, explaining that rain means “the baddies can get to one another”, something near impossible when the narrow streets in west London are rammed on a sunny carnival day.

Fears of violence this year amid a rise in knife crime have led police to deploy electronic knife arches at the carnival for the first time. But plans exist to be thwarted, and the incessant rain means some of the arches are not working.

“Rain is effectively the knife arch,” quips one officer.

The weather means carnival crowds are about half of what was expected, so when Musker chairs a 4pm phone conference of the emergency services and the government, he is able to declare: “At the moment it is peaceful in Notting Hill.”

However, the weather on Monday is expected to be dry and relatively warm. It seems like everything presents a challenge. Musker predicts it will be “a very busy day”, adding: “Bear in mind people who have not come today will come tomorrow.”

Musker’s command suite sits in the corner of the Met’s main command centre. Close by are those in charge of armed officers, specialists in tackling violence, managing traffic and monitoring social media.

As he talks he glances at the screens and decodes the pictures, a skill he says he got from years of experience on the ground: “The screens are a guide, not a bible.”

Facebook Twitter Pinterest Police officers on patrol on the main Parade day of the Notting Hill Carnival Photograph: Daniel Leal-Olivas/AFP/Getty Images

Those in command of the carnival have their own jargon. One thing that raises concern if spotted on the screen is “bomb bursts”, when people in a crowd suddenly run away, and which might be the first hint of trouble.

Musker adds: “You can’t understand sentiment and feel from sitting up here.”

As CCTV cameras show young men jumping around he jabs a finger at a screen: “What looks really lively could be high spirits.”.

Musker leads the operation as gold commander for the fourth time. The cameras inform and can also capture crowd crushes and other horrors unfolding. “I’ve sat here and seen one of my officers flat on their face, with their finger in someone’s artery [after they had been stabbed], with people walking by kicking him,” he says.

“Sometimes there is a tension between what we see and not demonising a community event.”

Musker explains that if commanders are concerned about a crush, the police helicopter can measure the heat emanating from the heads of people in a crowd. If people get scared their head generates more heat and shows up as white on video screens, rather than dark. The problem is it may be too late by then, and decisions that baffle revellers – closing off roads or refusing access to carnival areas – can just be the police anticipating problems 30 or 40 minutes before they actually happen.

Facebook Twitter Pinterest Some Londoners undeterred by the heavy rain. Photograph: Neil Hall/EPA

On Sunday police made 38 arrests at the carnival, and recovered two knives and a Taser.

Musker says he decided on Saturday evening after reading intelligence reports about violence to declare all of the carnival on Sunday an area covered by section 60, allowing officers to carry out stops and searches without the need for reasonable suspicion.

With one million or more people thronging narrow streets in west London, the carnival is the biggest annual public order challenge for the Met.

Some members of the black community dislike the police and the media focus on the Notting Hill carnival as a crime story, rather than Britain’s biggest annual celebration of African-Caribbean culture. And while some feel it has been finishing earlier with too many restrictions, others say it should be moved and restricted further.

Musker makes it clear he opposes any later finish and says: “What I want is new thinking to make it a safe and spectacular event.”

On the ground those who braved the rain observed a 72-second silence for the victims of the Grenfell fire, which happened close to the carnival route.

Matthew Phillip, the executive director of Notting Hill carnival, said: “What an incredible day – no matter how much the rain came it couldn’t dampen the spirits of all the children taking part in today’s parade.

“It was an incredible display of colour and music from the 72 bands.

“We’d like to thank all of the brilliant performers for entertaining the crowds and putting some sunshine into the carnivalists day.”