Weather forecast in Japan is worse than throwing a dart

[7-seasons.com]

Does anyone know why/how the weather forecasting is so terrible in Japan? Am I using the wrong source? Do they have a locally based weather office? Or is the weather seriously this hard to predict specifically in Japan? I have lived in 3 countries and a few cities, but this is absolutely the worst and very noticeable.

The temperature forecast seems to be pretty good but the weather is frequently way off. I should say that I had already given up on the weather forecast and bought my own barometer to get the atmospheric pressure haha. My personal forecasting based on looking at the clouds, feeling the wind, and checking my barometer doesn't do so well for gauging let's say rainy season and typhoons for example.

I seriously feel like this is an entrepreneurial opportunity because it is so bad unless it is like the episode of Curb Your Enthusiasm where the weatherman was forecasting rain to clear the golf course and have it to himself.

Examples:
1. Many occasions previously where I checked the weather for tomorrow the night before (good ol rush hour days to the office), and woke up to confirm/check again and the forecast for now today has completely changed at 7 or 8 am on that day. Like, somebody wakes up and updates to completely change the forecast when the day has already arrived.
2. Rainy season: this one was on the Weather app on the iPhone, maybe Accuweather, I checked it on the first day of rainy season. It showed 2-3 weeks of rain every single day. The result? It rained for maybe 3 days for the whole "season" and stopped short.
3. Typhoon 4: JMA website. I first checked this because a coworker said she was leaving early to go back to Korea before the typhoon hit Tokyo. I am pretty sure that at the very start the typhoon was headed straight north to Korea on the JMA website. Then, a day or two later the forecast showed a hook right directly to Tokyo that was supposed to arrive today. And the result? The typhoon died and stopped right on Kyushu.

Feels good to rant about this so I am already somewhat satisfied but if anyone has a better forecasting source or a rationale for why the forecast is so bad I could stop complaining a little bit. And if someone has tips for forecasting by myself that would also be appreciated!

[RetireJapan]

In my experience Yahoo Tenki is much better than the iPhone/Android weather apps. The local news seems pretty good too.

[goran]

Yahoo Tenki for the win.
I like their cloud and rain mapping animation for next few hours, which I'd say is fairly accurate as well.

[Beaglehound]

I wouldn’t write off JMA. I find it extremely accurate for hourly forecasts. On why forecasts are often inaccurate, so much sea and so many mountains makes things inherently unpredictable is my uneducated guess.

[captainspoke]

I wouldn’t write off JMA. I find it extremely accurate for hourly forecasts. On why forecasts are often inaccurate, so much sea and so many mountains makes things inherently unpredictable is my uneducated guess.

JMA data is almost certainly what every other service and app uses--those others just put their own skin on it to make it look unique. Does anyone really think that yahoo or any other secondary provider is doing anything other than scraping what's publicly available? (like JMA) The only 'competition' for JMA would be the US military, to the degree that they release their data to the public.

I use JMA all the time, all the time. I find it to be reliable. Note that in their weekly forecasts for a given place there is an A, B, or C included to indicate the reliability of the forecast (A = good, C = best guess).

Thinking some service can tell you what the weather will be a week from now is tentative, two weeks from now is dreamland. (tho I forecast it will be pretty hot thru the rest of July and most of August.)

[Deep Blue]

I find it exceptionally accurate compared to the forecasts in the UK.

[Andy.]

Concur on Yahoo Tenki. Pretty reliable for me.

[Gulliver]

Without getting too technical: Japan is geographically situated in one of the worst possible spots for accurate weather forecasting. There is a constant tug-of-war between the continental effect sweeping in from China/Russia and the maritime effect coming from the east since Japan is essentially a Pacific island. Added to the mix are wildcard typhoons from Southeast Asia being funneled between the two systems which may, or may not, have petered out by the time they get here.

During the extreme temperatures of a Japanese summer unexpected updrafts and cloudbursts can further complicate the matter. I’m sure we’ve all experienced enjoying a calm day one minute and suddenly having your hat blown off the next.

Also remember, when they say there’s a 50% chance of rain what they actually mean is that there is a 50% chance that any one spot in the forecast area will receive precipitation.

On top of all this throw in the extreme elevation inclines between the plains and the mountain ranges intersecting Japan- Going east or west 20 kilometers could place you in an entirely different climate.

Your best forecast is usually going to come from local meteorologists on TV evening news. Since these guys have local experience they are good at reading the situation about a day or two in advance. When I first moved here I thought it was funny how they would suggest clothing to wear the next day and whether you should bring a small folding umbrella or a big strong one. But it turns out they know what they’re talking about.

Due to the conditions outlined above attempting to make an accurate weather forecast one or two weeks out is conjecture at best.

[captainspoke]

... When I first moved here I thought it was funny how they would suggest clothing to wear the next day and whether you should bring a small folding umbrella or a big strong one. ...

Where we are there's a saying something like "it's okay to forget your lunch, but you should never forget your umbrella".

**

Separately, what you said rang bells, and if anyone is interested read about the Siberian High and Aleutian Low.

https://en.wikipedia.org/wiki/Siberian_High

https://en.wikipedia.org/wiki/Aleutian_Low

[Cracaphat]

My wife always believes her newspaper's BS forecast.She just set in her ways regardless of how many times they're wrong.I use The Weather channel app for myself.