It's the first day of September. What this means, to the whole of Japan, is that it's now autumn. Forget the vernal equinox, put a jacket on, ignore the blazing sun outside. Autumn has arrived. Fashion magazines are full of autumn outfits and shops have set out their Halloween displays.
The Japanese take great pride in the fact that Japan has four distinct seasons. The weather forecast on TV is reliable down to the hour. If it's meant to be raining at 10am but just a bit cloudy at 11am, you can bet money that the rain stops at 10.59 on the dot. You will see people dutifully lugging umbrellas on hot, sunny days, because the forecast said there'll be some drizzle at 4pm.
In contrast to our often unpredictable British summer weather, you know when it's summer in Japan. And you know when it's not. If we're going by changing temperatures and orange leaves, it is not autumn just yet.
But this isn't completely about the weather, either. Sure, September just started, but it's going to hit at least 27 degrees in Tokyo all week. The daily temperature isn't going to drop below 18 degrees until the end of October. So what's going on?
The obvious answer here is marketing. It's a lot easier to advertise autumn clothes to people if you've made them believe it's time to wear them. After all, only the very forward-thinking amongst us would go shopping for jumpers and scarves in 27-degree heat.
Japan has a relatively 'immediate' approach to selling things - if you need it, you need it now. And you should be able to find it now. In England, Sod's Law dictates that you won't be able to find an umbrella when it's raining. At the first sight of precipitation in Tokyo, every shop you pass will be flogging umbrellas. This is why autumn is forced upon the Japanese consumer with the start of September. If people wait until it's genuinely cold to buy autumn clothes, shops will have missed out on close to a month of sales.
Such a contrast between weather and mindset can be a bit disconcerting. I was last in Tokyo in the run-up to Halloween. As you can see from the picture, there were pumpkins everywhere. Wandering around shops filled with costumes and fake blood felt just like being at home. Eating pumpkin and sweet potato ice cream sure didn't.
I'm writing this under the shadow of an ominously grey and heavy London sky. In Tokyo, it's going to be something like 29 degrees today. So just where has autumn actually started?