TOKYO — With rain forecast for the next day, work took a back seat today to Tokyo’s cherry blossoms, in full bloom across the city.

Parks such as the popular Ueno Koen drew large weekend-like crowds, and even those who probably should have been somewhere else could not resist the temptation of the soft pink “sakura” and a gorgeous day.

“You see all these salarymen here?” said Ichiro Yamamoto, a 62-year-old office worker who sat eating a picnic lunch with two friends. “We’re all ditching work.”

An annual rite of spring in Japan, sakura season is not just about admiring the ephemeral beauty of the delicate flowers that disappear almost as soon as they emerge. The blossoms are also a great excuse to party.

Yamamoto and his buddies have been gathering in Ueno for the past five years, certainly to see the flowers but more so to enjoy each other’s company and indulge in good food and drink.

“It makes me feel like I’m really Japanese,” he said.

Sitting a few hundred meters (yards) away was Mizuho Kishi, 23, and two classmates from high school who had gathered for their first cherry blossom party in Ueno.

“It really feels like spring has begun,” Kishi said.

Her friend, Asami, who said she couldn’t give her last name because she cut work to be there, had never been interested before in cherry blossoms.

“But this is really the only chance you have to picnic with friends,” she said. “It’s a great part of our culture.”

All the festivity, however, isn’t exactly spontaneous.

Cherry blossoms are serious business in the country, especially for those in charge of predicting when they will arrive.

To get it right, the Japan Meteorological Agency uses a supercomputer to create a map and schedule of each year’s cherry blossom “front” that moves from the warmer south to the colder north. The data is then used by millions of people in Japan to plan their cherry blossom parties and get-togethers.

When the agency gets it wrong, as it did last year, officials offer public apologies for their miscalculations.

Sakura in Tokyo reached full bloom this year nine days sooner than average and the third earliest day since 1953, when weather officials began keeping track. The agency announces that the city’s cherry blossoms are at their peak when more than 80 percent of a benchmark tree at Yasukuni Shrine has flowered.

Newlyweds Heather Mannion and Eric Bahm of Oakland, Calif., were spending their honeymoon in Tokyo this week but said their timing with the cherry blossoms was pure luck. As they strolled under a tunnel of pink, Bahm said he admired how the sakura bring together young and old, rich and poor.

“Everyone lets loose,” said Bahm, a high school social studies teacher who lived in western Japan in the 1990s. “They revel in being together.”