The first thing Gu Zhiwei did after traveling through time was get dragged away to forecast the weather.

One moment she had been watching a typhoon’s path at a modern meteorological station. The next, she was kneeling in a wooden room with a leaking roof, facing three officials. A bronze plaque on the desk read Bureau of Winds. On an old map hanging from the wall, the river outside the city had been circled three times in red.

“There will be heavy rain tomorrow in the late afternoon,” she heard herself say. “The mountain flood will reach the south gate within half an hour.”

The chief official set down his brush, his face darkening. “Young lady, the governor is getting married tomorrow. Move the rain to the day after.”

Gu Zhiwei thought she had misheard. She asked for the map, spread it on the floor, then checked the shape of the cloud base outside. She had no satellite and no radar, but the wind direction, air pressure, and color of the river gave her enough to go on. The south gate was low ground. More than four hundred families lived there.

“Rain isn’t a government notice. You can’t change its date.”

The official gave a short laugh and pulled another sheet from his sleeve. It was the Bureau’s official forecast for tomorrow, already stamped with a seal. It said Clear skies.

Gu Zhiwei remembered the hardest part of a typhoon night: people did not always disbelieve a forecast. Sometimes they would only believe someone willing to bear the consequences of acting on it.

She turned the forecast over, wrote down the elevation of each lane near the south gate, and began calculating where the first evacuees should go. Someone outside shouted that the river embankment had split open.

Before she could finish, the old map fell from the wall. Behind it was an older one, its paper yellowed but its writing clear: Thirty years ago, same month, same day: south gate submerged.

At the bottom, in small characters, was the signature of another colleague from her modern weather station—a person she had never met, yet knew all too well.