Beijing — A storm front Monday forced the Solar Impulse aircraft to make an unscheduled landing in Japan, the latest setback for a project that’s attempting two solar-powered “firsts”: flying a plane cross the Pacific and around the world.

Before landing in Japan, however, the plane had traveled for 40 hours, completing the first day-and-night leg in its planned around-the-world journey. According to the Solar Impulse team, it was the longest solar-powered flight ever.

Pilot Andre Borschberg set off from Nanjing, China, early Sunday with hopes of flying the Solar Impulse continuously to Hawaii, which no one has done before in an aircraft that carries no fuel. As Borschberg soared over the Sea of Japan, his ground crew cheered him, tweeting repeatedly at the hashtag NextStopHawaii.

But a storm front that was east of Japan closed in on the plane’s flight path, according to Bertrand Piccard, initiator of the Solar Impulse project and Borschberg’s co-pilot. That forced Borschberg to slow the plane as the team assessed options. On Monday afternoon, they decided he should land in Nagoya, Japan. According to the Solar Impulse website, the plane landed safely at Komaki airfield just before 11 p.m. local time.

“The window to reach Hawaii has closed. The front is too dangerous to cross,” Piccard said in a video message posted on the Solar Impulse website. “So we have decided to land in Nagoya and wait until weather conditions are better to continue.”

Swiss pilots Piccard and Borschberg are taking turns flying the lightweight, one-seat plane. The product of a decade of work and fundraising, Solar Impulse gets its energy from 17,000 solar cells on its 236-foot-wide wings, which are wider than those on a Boeing 747.

In 1999, Piccard led a two-man team that became the first to encircle the globe nonstop in a hot-air balloon. He then launched the Solar Impulse project to see whether advanced technologies could propel a plane around the world without fuel.

Piccard said the team was pleased with the plane’s performance — citing its lengthy flight even after the sun had set — and that he was convinced the aircraft was fully capable of flying across the Pacific, although there might be more bumps along the way.

“Adventure is like this,” he said in his video message. “No, we are not going on a holiday trip.”