During the planning phase of trips to Japan, I monitor two data sources in tandem. The first is that ever-shifting results screen, responding in real time to seasonal demand, route changes, currency shifts, and consumer behaviour. It tracks the rise and fall of flight costs and availability—a volatile, networked system, self-adjusting yet entirely human-made. Its only near certainty is that the longer one hesitates to buy, the worse the deal becomes for whoever’s left holding the credit card.

The second data source, by contrast, is influenced only in microincrements by human activity spread across years, decades, even millennia. It remains largely indifferent to the compressed timescale of a trip, shifting and settling on its own terms. It is, of course, the weather, a determinant on the kind of walks, travel, and work I’m likely to undertake. Both the weather report and the flight screen have been on my mind this week, with my September arrival in Tokyo drawing near.

September is classically the first month of Japanese autumn. Early on, it still feels like summer. The air clings with humidity, and daytime temperatures often exceed 30°C, driven by typhoons and their trailing weather systems. Precipitation is likely, especially in the first half of the month, as autumnal rain bands sweep across the archipelago. Toward October, stable air masses suppress cloud formation and begin to take hold, bringing clearer skies, cooler air, and an easing of the heat. I’ve always found September a moving time to be in Japan.