u/Neko_Dash

  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.

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

Good evening. Stayed up a bit late tonight to get the latest data from the Joint Typhoon Warning Center on the approach of T15 to the Japanese mainland.

Currently, T15 is located at 35.5N 147.9E, putting it about 740km east of Yokosuka, Japan. The storm has a measured central pressure of 990 hPa, with sustained winds of 72kph and is moving northwest at about 20kph.

T15 is barely a typhoon by any measure, making the cut in the JMA's domestic definition by the narrowest of margins. The US-operated JTWC calls it a tropical storm. Nonetheless, it is heading straight for Japan, setting up our first direct, near-perpendicular hit on Honshu since 2021.

As noted earlier, T15 is not a strong storm. It is operating in a "marginally favorable" environment. It does have healthy outflow, meaning it is clearly pulling up moist air and is expelling it at altitude, but some wind shear has been observed near the southwest periphery of the storm, affecting its overall integrity, and it is in a somewhat cooler sea surface temperature environment.

Overnight tonight, T15 will start to turn west-southwest in reaction to a strong ridge of high pressure pushing down from a strong high system holding in the northern Pacific. It will also slightly intensify on its final approach to the Japanese mainland, although that will not move the needle much in terms of overall storm strength.

https://preview.redd.it/wokv67w2nkih1.jpg?width=2668&format=pjpg&auto=webp&s=decff168c220b7b4ad53c31e93162b31f8d2cd80

High pressure from the North Pacific is acting as a steering mechanism for T15.

Forecasted pressure gradient profile of T15 upon landfall. Blue indicates decreasing pressure, meaning you are in the path of the storm and green is increasing pressure seen from the back side of the storm after it has moved past.

Current data suggests landfall south of Mito, near the border of Chiba and Ibaraki prefectures at around 18:00 tomorrow, 11 August. The storm will begin to lose intensity almost immediately after coming ashore, and it will cut west-southwest over Kanto and the southern Japan Alps. By Wednesday morning, it will emerge in the Sea of Japan around Fukui prefecture as a low pressure system, downgraded from its stronger storm status.

Rainfall from T15 will be focused in central Japan, with accumulations of between 60-120mm expected in the 24 hours between 15:00 11 Aug - 15:00 12 Aug along the direct path of the storm. Areas in the periphery of T15's path will get lower totals. Winds on the Chiba/Ibaraki coast at landfall will be between 50-80kph, but will decay rapidly as the storm moves over land.

Stay safe wherever you are!

Attention all personnel! Just as an FYI, I rejiggered the flair a bit to focus more on weather events instead of geographic location (with an example shown above).

We do have user flair available if you want to show where you're chiming in from.

以上

  Last night's strong string of pop-ups last night included some excellent pyrotechnics as a bonus.  Absolutely hellacious rainstorms from afternoon to evening from Nagano over to Tochigi, down to Saitama and into Kanagawa as a group of very energetic convective storms blew up in the elevations, came down, then got some backbuilding to keep the tempo going.

  Today, we expect calmer skies and cooler temps for much of the nation.  Pop-up risk declines and centers on the Shizuoka-Aichi area.  T15, meanwhile, begins its approach to Japan.   Let’s talk about T15 for now and get into what to expect, and not expect, as we get a relatively rare Tohoku direct hit from a typhoon.  First off, T15 is not a strong storm, by any measure.  

  Current T15 snapshot

  Central pressure: 990 hPa as of 10 Aug, 09:00 JST

  Location: 33.8N, 149.7E, about 900km east of Yokusuka, Japan

  Movement: Northwest at 15kph

  Sustained Winds: 72kph; Gusts: 108kph

  

High pressure (depicted in red) is steering T15 (tight blue circles) on a more southerly course than originally thought.

Landfall profile of T15, around 17:00 Tuesday, 11 Aug.

Most of the rain action on T15 is in the northeastern part of the storm.

Anticipated T15 rainfall accumulation for the 24 hours from 15:00 Tuesday 11 Aug to 15:00 Wednesday 12 Aug.

  T15 is a typhoon according to the JMA’s definition of a typhoon, but only barely.  What’s going to happen from here?  T15 is in a “marginally favorable” environment, which means that it can maintain its strength as a storm, but there are factors preventing it from growing.  Warm sea surface temperatures and very low wind shear are helping the storm continue its current intensity, but drier air to the south and west of the storm are preventing further development.  T15 is being steered by a huge crest/ridge of high pressure which extends over most of the northern Pacific.  An extension of this high is deployed over the Sea of Japan and the Korean Peninsula, forcing T15 to a more southerly course than previously anticipated.  There may be some opportunity for T15 to develop prior to hitting land tomorrow, but the storm will not present a large threat to communities in its path.

  Until yesterday, T15 was expected to make landfall Tuesday afternoon near Sendai, but current models suggest the storm will come ashore further south, closer to Mito, in Ibaraki prefecture late afternoon (around 16:00-17:00-ish) on Tuesday.  The steering mechanism I mentioned above will also give a push to T15, and its flyover Honshu will be finished in about 12 hours, re-emerging over the Sea of Japan as a much weaker system around 4:00-6:00 Wednesday.

  Rain accumulations for the 24 hours from 15:00 Tuesday to 15:00 Wednesday can be expected to range anywhere from 20-80mm, depending on where you are in the path of the storm, with local amounts of up to 100mm possible.  Most of the action in T15 is happening on the northeast side of the storm and areas on the southwest side of the system will see lighter rainfall.  Winds upon landfall will range from 50-80kph, which is right on the fence as far as JMA definitions of typhoons go.

  Because of T15’s location and cyclonic rotation, much of Japan along a line from Shizuoka to Hokuriku on up north will get a few days respite from the summer heat we have been having.  High temperatures between today and Wednesday the 12th tell the story.  Tokyo goes from 32 to 27, Nagoya from 36 to 28.  Osaka and Kyoto both will follow the same curve.  Gifu City, too, will see Monday’s high of 36 drift down to a more tolerable 31.  Kind of the reverse of what we would expect after a typhoon, right?  Again, it is all about positioning, and instead of pulling warm tropical air up in its wake, as a normal typhoon does, T15 will drag more northerly air down.  Enjoy it because by the weekend, temperatures nationwide will rebound to more seasonal highs.

  That’s the wrap up.  The countdown to T15’s landfall starts now.

As we get moving on this fine Saturday morning, the eye of Typhoon 13 has moved past Okinawa, but the island chain is still be thwacked by the leeward side of the storm and still has to deal with a few more hours of carnage.  T13, while still a very, very formidable piece of atmosphere, is decaying.  It will move over into the Asian mainland, devolve further, and bring heavy rains with some flooding to that area over the next few days.

The current scoop on T13

Expected rain totals as T15 moves across Japan

The current dish on T15 as it forms in the Pacific

In the meantime, a smaller bubble of a typhoon has formed out the Pacific.  Designated Typhoon 15 by the JMA, it was just promoted overnight and has sustained winds of just 65kph.  While that barely puts into the typhoon category in Japan, it is still classified it as a tropical storm elsewhere. 

About two days ago, I said on this sub that T15 was going to give Japan a “full and clean miss” and I now need to retract those words.  Newer models for T15 have been generated.  Earlier it appeared that there would be no strong steering mechanism for T15, which would allow it to swing north unhindered and miss Japan altogether.  More recent models tell a different story.  While the current high pressure system steering T15 will disintegrate, this will give T15 a short chance to jink up northward some, but another high (a “ridge” as we call it) will take its place and force T15 on a more east-to-west course, bringing it to a very uncommon path of landfall around Tohoku, specifically, Sendai.  T15 is projected to grow only modestly as it winds up for its rare track toward Japan. 

By midday, 11 Aug, T15 should boast 85kph winds and bring a metric buttload of rain to the Tohoku, Kanto, and Hokuriku areas, with between 50-80cm rain possible from the storm.  Chubu and Kansai, too, will benefit from the waterworks with an expected 15-25cm of rain as T15 winds its way over the Japanese archipelago before finally limping on out to the Sea of Japan and over toward the Korean Peninsula.

Typhoon 14, just to note, formed and died just as quickly west of the Philippines.

Everyone, have a great weekend. It is now time for me to shut down the computer and go touch grass and commune with nature for a bit. Stay dry and stay safe, y'all.