r/japanweather

Take care, everyone!

  This is tough, because I generally respect science and academia, and have profound reverence for those who hold doctorates in scientific fields.  However, the Asahi Shimbun on August 14 maneuvered into scare tactic territory and it needs to be called out. The article is here: https://www.asahi.com/ajw/articles/16808645

  At contest here is the assertion by a professor emeritus of meteorology at Kyushu University that a “monsoon gyre” is behind the recent paths of T15, which came ashore at Ibaraki prefecture on 11 Aug, and was the catalyst behind Chiba’s torrential rains two days later.

  Let that sink in: a professor emeritus.  That is a very high ranking individual in the halls of scientific academia.  The meteorologist quoted has dedicated his entire life to the study of the science.  On the other hand, I am someone who lacks such academic distinction.  I have been reading weather charts and cataloging atmospheric phenomena for 45 years.  I chased storms in the dead of night with my buds Jim and Bryan along some of northeastern Oklahoma’s lesser-known roads back when all you had a was a glitchy AM/FM radio, a cheap CB radio, a worn-out paper map and an inconsistent flashlight.  I am passionate about the science, and I am dedicated, but I am not a doctorate in the field by a long shot.

The approach of T15 was steered more by strong high pressure in the North Pacific rather than any southerly low pressure activity.

If you look at pressure tendencies of T15 as it approached landfall, there is almost no pressure change to the southeast of Japan. Gentle pressure slopes like this do not - can not - steer typhoons.

Surface analysis for 19 Aug. Lows in the tropical Pacific begin to dissipate. Data from ECMWF.

By 21 Aug, tropical lows may again re-establish themselves.

  But I’m still going to sound off because some things here do not sit right.  Let me go through my contentions, complaints and nit-picking here.

  Nitpick 1) A “monsoon gyre” steered T15 and fed the moisture necessary for the Chiba deluge.  My counterpoint: Typhoons, for all their ferocious power, are really just really big low pressure systems.  They are steered more by high pressure areas than lows in the vicinity.  T15 was steered from a strong high located in the North Pacific.  There was not a strong presence of lows in the Pacific southeast of Japan at the time of approach and landfall and steering effect by them would be marginal at best.  By the time the 13th rolled around, there were some stronger lows in the tropical Pacific southeast of Japan, but the Pacific high, too, helped funnel warm, moist air into Kanto.  That, with some cooler, drier air aloft, sparked the storms we saw a couple of days ago.  It was not, by any means, a solo effort from the gyre.

 Nitpick 2) Overhyping the gyre, being super vague and selling panic.  My counterpoint: This one complains about the Asahi’s reporting.  First off, a monsoon gyre is an informal title given to a group or cluster of lows which more or less act in unison.  It is not a cohesive system, like a typhoon nor is it a fully-defined phenomenon, like a front.  It is a situational happening.  A train of lows working kind of in concert for a period of time.  The JMA does not recognize a gyre, doesn’t declare one, and it will be on none of their charts or maps.  A gyre, in other words, is pretty much in the eye of the beholder.  The professor wants to see a gyre, fine.  To me, though, it is a just temporary band of lows that fade in and fade out. 
  The Asahi quoted the professor as saying the gyre framework will last for about two weeks, which will make you think at first blush that this instability will continue through the end of August.  However, buried in the article, the professor notes that the gyre formed in early August.  My data shows a break-up of lows to the southeast of Japan from around August 19, with a possible re-clustering a few days thereafter.  Two weeks from the first part of August?  Yep, that lines up.  But major boo to the Asahi for ginning up a bit of panic with a carelessly written headline.

  Nitpick 3) Is it a gyre in the first place?  My counterpoint: No.  Gyres do exist, but not here.  We have had lows extending out southeast of Japan for a while, since the end of rainy season.  They form, merge, dissipate, a high will come in for a bit, then a low will move in, and the process begins again.  I don’t see it as a gyre, but my own definition of a gyre is something a little more solid than just a temporary, two-week fix on a weather chart.  Of course, if you take away the gyre as the “baba-yaga” of the article, then you have no article.  They needed a boogeyman to support their thesis that something strong and wicked was driving the weather. 

  Nitpick 4) Is there a Japanese version of this article?  My counterpoint: I ransacked the Asahi’s Japanese-side site to corroborate this article and found nothing.  Was this printed only for the English language side?  If so, why?

  My forecast: Skies over Japan are going to settle down from tomorrow through 19 August  The current cluster of lows in the tropics (and, FYI, I will be very, very, very drunk before I call this particular formation a “gyre”) will weaken and dissipate in that time, but a regeneration is possible around the 21 August as a potential new invest pops up near the Mariana Islands and may become Typhoon 17.  21 Aug, however, is still a solid week away and, before I commit to the model, we need bring things in a few days and see what will happen.  By Monday, we’ll have a better idea. For the near-term, though, we will have a bit of a chance to dry out and get some sunshine.

Is this part of a typhoon or something else?

Unstable and shaky upper-level conditions dominate the vast portion of Japan today, bringing with it a risk of afternoon convective thunderstorms, some of which can be severe.

I cannot say for sure if we're going to get a repeat of last night's insane boomers in Chiba, or if movement of that type will happen in Chiba or somewhere else. The entirety of the nation, specifically Kanto, parts of Chubu, Kansai and Shikoku have very high chances of afternoon pop-ups, and that makes it pretty hard to nail down exactly where a storm/line of storms will build.

Looking at the 24 hour sat movie from 12:00 noon yesterday to 12:00 today, you can see most of the heavy activity began to flare at night. We only have IR for nighttime readings, but you can see thunderheads form and move as classic backbuilding kept feeding the storms into Chiba. We do have parallel conditions for this type of activity again today, so I would not put it out of the realm of possibility, but it's very hard to tell when/where any energetic motion will take place.

National radar as of 12:15 this afternoon indicated lots of weather action. Most prominently, there is a cluster of heavy storms in southern Miyagi prefecture, as well as a heavy cell on the Ibaraki-Chiba border. Some other smaller, but still very intense storms were seen in Ishikawa, Okayama and Kagawa prefectures.

Other widespread convective storms are predicted to pop-up today in the interior highlands of Kanto and Chubu.

I urge caution and keep your eyes on your radar apps as any one of these systems can, with a little push from the right updraft at the right time, build into a major storm cell with little notice.

Otherwise, hot and muggy across the country today. Some cooler areas on the Tohoku Pacific coast and Japan Alps highlands. No weather systems of note (typhoons, fronts, etc) today, and most of our weather activity for the next 24 hours will be powered by simple local instability at altitude.

Upper-level instability/Pop-up Thunderstorm risk today. Purple is a greater risk, yellow is a lesser chance.

National radar image, JMA @ 12:15pm 14 Aug 2026

24 hour satellite pic from yesterday to today, showing the dramatic building of yesterday's thunderstorms

Hi there!

Will be in Japan in late August. There is typhoon weather hitting Tokyo and I hope it ends very soon. In the meantime, what can I do every day to hide from the storms but also enjoy my time in Japan?

I will be bringing a rain jacket/umbrella/jeans/leather boots to protect me, but the high humidity is tough as well.

Any thoughts are welcomed and helpful!