u/Neko_Dash

  ...And you live anywhere from Kanto on down, you’ve probably noticed that it is raining.
  Nothing much to see, just a typical rainy season frontal pattern.  Moving east-northeast, a thick band of rain is moving along the western and southern half of the country, stretching from Kyushu all the way to Kanto.  Locally heavy rains pelted areas of Kyushu today, and intense precipitation down south will continue through the night.  The bulk of the rain will travel along the country, bringing a sloppy Thursday morning commute from Kyushu and Shikoku on up through Kansai, Chubu, Kanto and on up to Sendai.

  Rains associated with the front are expected to settle down by Friday, bringing partly-cloudy to cloudy conditions along much of the country.

  Tohoku and Hokkaido, meanwhile, may see some scattered rains here and there, but will largely be free of the precipitation tomorrow.

Rain patterns over Japan, 1 Jul @ 21:00 JST

The GFS projection of the new (as of yet unnumbered) typhoon's landfall over Taiwan. Forecast date: 10 Jul, 21:00 JST

The EMCWF's data run shown the new typhoon bearing just a little more north, bringing a wet day to Okinawa. Again, forecast for 10 Jul, 21:00 JST

Development of Invest 95W from 30 Jun, 21:00 - 1 Jul 21:00 JST

Meanwhile, we have two developing typhoons in the tropical Pacific.  One, developing just to the west of the Philippines, is expected to move into the Asian mainland soon after it forms.  The other, named, for now, Invest 95W, which we covered yesterday, has plenty of room to grow.  Compared to yesterday’s satellite images, the storm has a bit more development, and that patch of the Pacific is prime for cyclone growth right now, with sea temperatures of around 29-30c, giving the new storm lots of fuel.

  Long term models are beginning to coalesce and the current consensus is that this storm, which should reach typhoon status as per the JMA within the next the evening of 2 July, can become one of 2026’s more serious events.  Projected paths of this soon-to-be typhoon are currently forecasting it to run well south of Japan, with both the ECMWF and the GFS projecting runs toward Taiwan then on into the Chinese mainland around 10 Jul.

  Of course, we are still 9-10 days out from that point, and a lot can happen in that time.  Even though things right now look like this typhoon will not be a direct player in Japan’s weather (with the very real potential exception of Okinawa getting a day of very heavy storms), we do have to keep one eye open just in case something starts to steer the system up our way.

Way, way out in the Western Pacific, near the remote atolls of eastern Micronesia, a small pocket of atmospheric instability has bubbled to life. Centered roughly 3,900 kilometers southeast of Tokyo near 9°N, 165°E, this broad disturbance is currently designated as Invest 95W. As things stand now, it is a loose, disorganized cluster of clouds and thunderstorms slowly rotating around a developing center, with sustained winds hovering around a modest 35 km/h.

However, the environment in this patch of the Pacific is extremely promising for cyclonic development.  With exceptionally warm sea surface temperatures and low wind shear - the winds aloft that can tear a developing storm apart - surrounding conditions are highly favorable for growth. Over the next 24 to 36 hours, the system is expected to steadily consolidate. Forecasters anticipate it will climb the atmospheric ladder next week, graduating from a tropical depression to a tropical storm, and finally into a mature typhoon.

Despite this high confidence in its formation, trying to plot an exact path right now is a bit of a nonstarter. While major global weather models and the Pearl Harbor-based Joint Typhoon Warning Center acknowledge its potential, long-range tracking models show absolutely no consensus beyond 4 July.

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To illustrate just how erratic early typhoon forecasting can be, the European (ECMWF) model projected a landfall near Nagoya on 11 July during Sunday's run, shifted its target to Korea on Monday, then today points toward Taiwan around 10 July.  Meanwhile, the American (GFS) model initially hinted at a direct line toward the Kanto region, only to later shift its tracking data south toward Okinawa.

So, the bottom line? We are looking at a system that has all the ingredients to become a formidable typhoon, but we simply cannot know where it is going yet. By 5-6 July, as the storm establishes a well-defined center, the steering currents will become clearer. For now, it’s just an active watch-and-wait situation.

By the way, a word about tracking models:  When a storm like Invest 95W starts brewing, it’s only a matter of time before multi-model tracking charts, aka “spaghetti models”, start flooding your social media feeds. If you’ve ever seen these charts, which look like someone threw a handful of multicolored noodles onto a map of the Pacific and decided to call it a day, it’s easy to think these tracks are a study in randomness.  But, there is some science here.

Here is how you should actually read them:

• Treat early lines as possibilities, not promises: A multi-model isn't showing you ten different guaranteed paths; it's showing you a range of mathematical guesses based on slightly different initial data. When a storm is this young and far away, the computers are working with a lot of missing pieces.
• Look for the bundle, ignore the outliers: Don't freak out over the one wild line that darts away from the rest toward your city. Pay attention to where the majority of the lines cluster together. That bundle of lines tells us where the highest probability lies.
• The farther out, the wider the spread: A forecast model is incredibly accurate for the next 48 hours. By day five, it's a bit blurry. By day ten? It’s mostly educated guesswork. If the lines look like a tangled, wide-open mess next week, it means the atmosphere hasn't made up its mind yet—and neither should you.

The Golden Rule: When a potential typhoon is more than a week away, use that time for awareness, not anxiety. Keep an eye on the official agencies like the Japan Meteorological Agency (JMA) or the Joint Typhoon Warning Center, and let the models sort themselves out over the next few days. We'll be tracking every data run right here.

The remains of T7 are out at sea, carried by the Jet Stream, and T8 lies tattered and strewn across the Pacific Ocean, like all the hopes and dreams of my youth.

It has been an eventful few days on the weather front here in Japan, along with a seismic jolt or two to spice things up.  So, what happens now?  

Well, we settle into a gentler rhythm of systems moving across the nation.  The rainy season fronts are offshore now (remember this…I’m going to refer to it a little later), and a high pressure system floating about in the Sea of Japan will largely dominate our weather for the next couple of days.  Through Wednesday evening, the country as a whole can expect partly-cloudy to cloudy skies and variable conditions with highs between 20-22 up north to 28-30 down south, with cooler highs in mountain areas.  Hokkaido saw highs between the mid-teens to around 20 today but will get a warming trend through the week, with highs in Sapporo reaching 26 on Thursday.  

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Summer time humidity - the heavy, muggy summer air we all know and love here - came into Kanto today, with daytime percentages hovering around 80%.  Most of the rest of the nation had drier daytimes today, but from Tuesday, Kyushu and Shikoku will begin to see midday humidities in the upper 80s as our next system begins to make its run across the country.

Our next weather player is expected to approach Kyushu from midday Wednesday, but the latest data suggests its track will stay south because of the positioning of the rainy season front (梅雨前線, Baiyu Zensen).  The rainy season front is not expected to move much over the next few days and will act as a conveyor belt of sorts for the systems coming over from the mainland.  High pressure domes both south and north of the front will also help channel the movement of the systems as they move across.

Rain is probable in most of Kyushu on Wednesday, then elevated possibilities exist in western Honshu, Kansai, Chubu (Nagoya) and Kanto through Thursday evening.  There will not be much time to dry out as the next system coming over from the Asian mainland is set to land in Kyushu on Friday and take much the same path, giving western Honshu, Shikoku and Kansai the greatest chance for rain as we head into the weekend.

  Anyone who lives in central Japan certainly felt the quake last night at around 22:30.  A light 6 on the Japanese scale and a M 5.7 from the USGS, it set off quake alarms over Kanagawa, Tokyo, Shizuoka among other locations as it fired off at a depth of 50.9km.  Ultimately, no significant damage came from the quake.

  On late in the afternoon of August 8, 2024, about one month after r/japanweather was created, the Hyuganada quake struck off the coast of Miyazaki Prefecture down in Kyushu.  That shaker came in at a light 6, too, with a USGS magnitude of 7.1, and set off at a depth of 25km.

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  In the aftermath of the 2024 quake, the JMA issues a “Nankai Trough Earthquake Extra Information” advisory, which is the somewhat tortured, direct translation of the 南海トラフ地震臨時情報 notice issued by the Disaster Management Division of the Government’s Cabinet Office.    The Nankai Trough, just for review, is a 900 km long submarine trench located off the southwestern Pacific coast of Japan. It marks a highly active tectonic subduction zone where the Philippine Sea Plate is sliding beneath the Eurasian Plate.   Mt. Fuji, at the easternmost side of the fault which created the Nankai Trough, was created by the geological forces coming from a collision of plates in the area.  

  The advisory noted that the August quake could cause instability along the Nankai trough, and, following historical precedent, a 7+ megathrust quake could potentially hit along the trough, which, in turn, could trigger a potential severe tsunami along the Pacific coast of the country.

  The thing that concerns me here is the August quake was near western terminus of the Nankai Trough.  Yesterday’s quake was near the eastern terminus.  

  If we could predict earthquakes, people much smarter than me would be making very direct statements about what to expect.   The problem is we do not know what will be next.  Nobody in the government so far has issued any statements connecting the two, nor has the JMA, the MLIT (Ministry of Land, Infrastructure, Transport and Tourism, 国土交通省) or the Cabinet Office announced any further warnings of quakes or other seismic activity.  There is a tidbit of historical activity about quakes along the Nankai Trough, and recent movements would suggest we are overdue for another one, but whether or not it will happen if very far from certain.

  I really want to be 100% crystal clear here.  I am in no way trying to gin up alarm or fear.  That’s one of the rules I set for the sub back in 2024 - no panic posts.  But, the locations and timelines of the two events should raise awareness that a large seismic event will eventually happen along the Nankai Trough at some point.  We simply do not know when the next quake will hit or how strong it will be.  Will it happen?  If so, when?  How large will it be?  Will it generate a tsunami?  Nobody knows.

Just be aware, keep alert and stay safe. That's the best we can do.

Links to government sources regarding Nankai Trough Warnings and Preparation

https://www.bousai.go.jp/jishin/nankai/rinji/index3.html

https://www.bousai.go.jp/jishin/nankai/pdf/multileaflet01.pdf

https://www.jma.go.jp/jma/kishou/know/jishin/nteq/index.html

  Although it sounds like an uncannily specific description of my ex-spouse, we are talking about the tracks of Typhoon 7 and 8 here, so stop snickering and pay attention.  Especially you troublemakers in the back.

  Now, then.

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  Typhoon 7 (data as of 18:00 JST): 

  Position: 24.8N 126.0E, 260km southwest of Kadena AFB, Okinawa

  Movement: 345 degrees at 18kph

  Max Sustained Winds: 82kph   Gusts: 144kph over open water

  Central atmospheric pressure: 985hPa

  Synopsis: T7 has lost a lot of its integrity in the past 24 hours.  24-36 hours ago, the eye was very visible from Himawari satellite images.  Now, not so much.  The storm’s strength peaked earlier today, and will encounter less favorable conditions from here on out.  It will complete its northeastward pivot at it makes its closest approach to Okinawa around 6am tomorrow morning.  After it pivots, it will pick up speed, pushed on by strong westerly winds aloft.  About 24-36 hours from now (26 June, 21:00~27 June, 03:00), it will encounter a double strike of drier air and more severe vertical wind shear (VWS...more on VWS a little bit below), as well as cooler sea surface temperatures as it moves out of the tropics.
  Where is it going?  After completing its pivot overnight, T7 will set a course for the Pacific coast of Japan’s main islands.  The path was tweaked a little eastward since last night, and the new path will put the Pac coast right in line for some very heavy rain.  Winds are forecast to run about 40-60kph along the southern Pacific coast, but maintain about 80kph over water.   Winds should taper down to about 30-45kph over land by the time the system reaches Shikoku onwards, and maintain about 72kph winds over water.

  Trying to forecast the rain profile has been tough, partially due to the weakening and loosening of the system.  It is also expected to merge with an existing rainy season front over Kyushu, Shikoku and the Kii Peninsula, which further muddies the waters, but is largely expected to extend the rain profile out toward Nagoya.  Suffice it to say Kyushu, Shikoku, western Honshu up to Kansai will be under rain.  Further up, Chubu (Nagoya) and Kanto will get significant rainfall through Saturday, locally heavy in some parts, while Hokuriku (the vicinity of Kanazawa, and up the Sea of Japan coast) will get some scattered bands of rain.

  Typhoon 8 (data as of 18:00 JST):

  Position: 19.7N 135.5E, 1,350km south-southwest of Kagoshima

  Movement: 315 degrees at 35kph

  Max Sustained Winds: 82kph   Gusts: 126kph over open water

  Central atmospheric pressure: 998hPa

  Synopsis:  The looser, faster one of the two, T8 is also weaker.  It is a scattered, weak storm on satellite images, with no discernible eye or even structure.  T8 is being pushed northwest along a band of high pressure out over open ocean.  Already pretty fast moving at 35kph, it will pivot along the endpoint of that high pressure band in about 12 hours (around 9am, 26 June) and then accelerate as it heads toward Japan.  In about 24-36 hours from now, (26 June, 21:00~27 June, 03:00), T8 will wander into the bad part of town, at least for tropical storms, and will get slammed by a very aggressive environment of strong VWS (vertical wind shear…remember…I talked about a bit up in the T7 passage), forceful winds aloft, surrounding dry air and cooler sea surface temperatures.  The result will take some of the edge off of T8’s strength, but the high winds aloft will assist in keeping T8 alive by maintaining storm outflow.

  Where is it going?  There is a lot of disagreement on the path of T8.  The JTWC says will move on a curved heading northeast and will make landfall around Shizuka, while WeatherNews is betting that T8 grazes Chiba around Saturday morning on its way out to sea, without any landfall.  Right now, it’s really up in the air for the 24-36 hours.  Anything can happen.

  Except the Fujiw(h)ara Effect.  Ain’t no way in this universe that’s gonna happen.  Period.

  There is also a chance that T8 may completely unravel by Saturday, depending on its vulnerability to the surrounding environmental factors outlined above.  If that happens, it will just be a line of thunderstorms instead of a coherent system.  Even so, it will still pack rain and winds.

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  Now, VWS.  Vertical Wind Shear.  What is that Y50,000 term?
  Typhoons for all their majestic, awesome power, are really fragile structures on a global scale.  Typhoons need very specific conditions to grow and thrive and system-scale challenges to that environment can bring a strong typhoon down to a tropical storm in a matter of hours.  The most common threat to typhoons is vertical wind shear.  In ideal environment for a typhoon is one where there is very little surrounding wind movement.  This allows the vertical cyclonic movement of a new typhoon to form and solidify.  Now, throw in some strong, sustained winds from anywhere from 2,000 meters on up at different speeds and directions, and that starts to mess around with a typhoon’s structure.   The central core (the eye) and its surrounding walls will start to degrade with persistent VWS exposure.  Down in the tropics, wind shear at that level doesn’t really exist much.  But, bring it up to around 25 degrees latitude on up, and vertical wind shear is more common. 

  Good morning everyone.  This is going to be a busy day on the sub, with the movement of Typhoons 7 and 8, and a steady rainy season front.  Lots to get through, but I want to go through the fun stuff first.

  On a couple of other Japan-related subs, there are some folks going on talking about T7 and T8 merging to create a super typhoon that will blow us all into Pyongyang along with our little dog Azuki.

  So, tell you what - let the other subs have their fun (and some of the creativity is a hoot to read), but here’s what really happens when the so-called “Fujiwhara Effect” takes place, why it is so difficult to see, and why it won’t happen in this case.

  The Fujiw(h)ara Effect is named after Japanese meteorologist Sakuhei Fujiwhara, who first described the phenomenon in the 1920s.  At that time, romanization of Japanese names hadn’t been standardized, so the extra “h” stuck in there, but like Stewie and his “h” pronunciation of “Cool Whip” on “Family Guy”.  But I digress.  Double Neko Points to anyone resident in Japan with the guts to say “Fujiwhara”, with the distinct “h” pronunciation, in every day life. [Images re-uploaded at the bottom of the post.]

Today's WeatherNews chart showing positions of Typhoons 7 and 8.

Course of 2019's T5. It ate T6 out over in the open ocean around 155 degrees E.

The atmospheric pressure profile of 2017/T5. It ate T6 around July 26, but there was no correlated increase in the strength. The red dip you see around July 30 was due to a more southerly track.

A satellite view of 2009's Typhoons 17 (L) and 18 (R) interacting. They did not combine, but the brief flirtation does make a stunning satellite image.

FUJIW(H)ARA EFFECT RUNDOWN

  Typhoons are massive low-pressure systems which rotate counter-clockwise in the Northern Hemisphere.  The Fujiwhara Effect posits that two typhoons within a certain distance of each other begin to influence each other and their low pressure centers begin to move to combine to create one storm.  This happens in one of two ways: 1) Stronger storm “eats” the weaker storm: This is basic physics.  The more powerful storm will consume the smaller member.  Or, 2) A Merger of Equals.  This is much more difficult to pull off, but two equals willl begin to orbit around each other until they merge. 
  In either event, the resulting storm generally does not become more powerful on its own.  If a storm is at 950hPa and has a radius of 500km before merging with a companion storm, the strength will probably not change.  The storm may become a bit larger, but generally not stronger.  I’ll address a couple of real-life observations in a moment.

WHY THE FUJIW(H)ARA EFFECT IS SO RARE

  Conditions must be absolutely perfect for storms to combine.  Being in general proximity alone is not enough.  Both storms have to be free of other disruptions, such as wind shear from other systems, high winds aloft (Minor Jets or Jet Stream), insertion of drier air from surrounding systems, landmasses, cooler water temps, etc.  The Fujiw(h)ara Effect truly needs a pristine canvas to create this particular painting.

HISTORICAL PRECEDENT

  So, I went back through the Neko_Dash Weather Library (known also as “The Internet”), and found that there was one recent instance of the Fujiw(h)ara Effect in the western Pacific.  in 2017, tropical storm Kulap (T2017/06) and typhoon Nori (T2017/05) merged, with the more powerful Nori eating Kulap for lunch, getting much stronger due to a southward dip into warmer, calmer seas, and then made a run for Japan coming up from Kyushu and over Honshu as a very pedestrian, not-very-noteworthy typhoon.  There merger took place out in open water, about 25 degrees N / 155 degrees E, far from any other systems which could have disturbed the merger.

  In 2009, there was a brief interaction between T2009/17 and T2009/18 (“Parma” and “Melor”) in the Philippines Sea, but it didn’t lead to a full merger.  T2009/17 went on to hassle the Philippines before smashing into Vietnam, while T209/18 hooked up north and did some time on Japan’s central Pacific coast.

WHY IT WON’T HAPPEN WITH T7 and T8

  The current T7 and T8 won’t combine and the biggest reason is because there is definitely not a pristine canvas to work on.  T7 is already weakening, wandering into a more challenging environment of hostile wind shear, drier air coming from the north and cooling sea surface temperatures.  T8 was never a strong storm to begin with and has remained disorganized.  Within 36 hours (that is, before 18:00 on 26 June), T8 will start to be picked up by Jet Stream-associated winds aloft and, that will be, for all intents and purposes, the end of the line for T8.

Any questions?

[Edit: For whatever reason, the images I uploaded are not coming through. Here they are again.

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But first, the weather.  The regular weather.

  There is a lot going on and Japan’s atmosphere right now is as wacky as a sack of cats.  There’s a lot to get through.

  It’s been a very cool summer so far, something that has been noted in other subs.  As much as this is cause for jubilation and dancing in the streets, especially after the brutal, brutal summer we had last year, our little cool wave is temporary.  It is the product of several factors, chiefly a proper rainy season setup, and placement of local high and low pressure systems bringing down northerly air.

Pressure and wind profiles of T7 and T8 as of 09:00 JST this morning.

This is why it has felt kind of cool. We have two very well-placed pressure systems funneling cool north wind down to us. Won't last forever, though.

Himawari Sat Movie for the 24 hours from 23 June, 09:00 - 24 June, 09:00.

​​  Looking at long-term data, I’m seeing a gradual weakening of this pattern in the July 1-4 timeframe, being replaced my more seasonal (i.e, hot) temperatures, probably with the standard humidity that goes with it.  Nationally, we will go from highs in the low 20s to the low 30s by 4 July.  Bottom line: Enjoy the cool summer now, while we have it.  By mid-July, we will have this memory and powerful AC to keep us cool.

  The 5-Day Forecast: The rainy season setups are still strong over the country, and they are being enhanced by the approach of couple of typhoons, which I will get to in a moment. 
  WEST JAPAN (Kansai on down to Kyushu, Shikoku inclusive): For the next three days, through the evening of 26 June, western Japan will be under rainy skies much of the time, with some of the rainfall, particularly in Kyushu and Shikoku, very heavy.  Much of this rain is generated from rainy season fronts, but the approach of Typhoon 7 on Friday will give the rain just a bit more strength.  Things will begin to settle out with the rain moving on by midday Saturday, and some areas may get some sun poking through the clouds on Sunday.

  OKINAWA: Okinawa will see their sunny weather turn to heavy rain with the approach of Typhoon 7 from Thursday evening (more about that later).
  CENTRAL JAPAN (Chubu/Hokuriku/Kanto): Rainy season frontal system-derived showers will fall over much of the central part of the country on Thursday.  Rain bands from Typhoon 8 and, later, Typhoon 7, will begin to be a player in central Japan’s weather from Friday as it moves northeast over Honshu.  The central part of Honshu and Hokuriku (Sea of Japan) side of the country are expected to get the most intense and sustained rainfall from the at-that-point rapidly weakening T7.
  TOHOKU/HOKKAIDO: Tohoku and Hokkaido both will see fair to cloudy skies today, with increased chances of rain on Friday as the remains of T7 push through the area.  Cloudy to partly cloudy skies remain in the area after the storm.

  TYPHOON 7 and TYPHOON 8

  We have something of a traffic jam this week, as both Typhoon 7 (aka, “Mekkhala”) and Typhoon 8 (aka, “Higos”) churn their way through the Pacific Ocean on their way to Japan.  There’s a lot to unpack here as these storms have very different characteristics.

  First things first: Models, although in general agreement about both T7 and T8 over the next 36-48 hours, then start to go all over the place regarding the path and intensity of each typhoon.   What follows is my interpretation of what each typhoon will do, based on data from the JTWC, WeatherNews, the JMA and the ECMWF.

  Typhoon 7: T7 is the stronger of the two storms in the Pacific right now.  The latest data runs on T7’s 5-day forecast position the storm further westward than before.  Its strength has already peaked, a day or two before its expected encounter with Okinawa and it will begin a. Slow decline.  Located as of 9:00 JST at 21.0N 124.6E, about 530km south-southeast of Taipei, T7 has a central pressure of 983 hPa and sustained maximum winds of 140kph with gusts of up to 170kph over open water.  T7 is executing its pivot now, presently tracking at 354 degrees, just a little west of true north at a lumbering 15kph.  It will move northeast toward Okinawa later today, and set a course over the main Japanese islands.  

  Once the recurvature is complete (that is, once it completes its pivot), it will pick up speed as it runs into stronger winds aloft coming from the west.  

  In the next 24 hours, T7 will begin to run into some hostile areas, with stronger wind shear which will tear at the integrity of the system.  About 36 hours from now, movement into cooler waters will further sap T7’s strength, although the outward flow aloft will continue saucking air upward and helping the storm maintain its fierce intensity through Tau72 despite the cold water.

  T7 will bring large bands of rain and some storm-level winds to Japan’s main islands through Thursday evening into Friday, finally moving away from Japan around Saturday afternoon.

  Typhoon 8 was classified as a typhoon-level storm by the JMA this morning, but it is just barely in that classification.  As of 09:00 JST, the storm had 72kph sustained winds with gusts of 108koh over open water and a central barometric pressure reading of 1000 hPa.  It is not powerful, as typhoons go, and it is not expected to develop much stronger than it is now.  T8 is not expected to make landfall, although current models suggest it will graze the Pacific coast of Chiba while staying about 100-150km offshore.

  Now, a note about these typhoons, and this is directed mostly to travelers.  First, typhoons, by the time they get up to the latitudes of Osaka or so, lose a lot of their power. They are still formidable storms bringing a lot of wind and rain, don’t get me wrong, but they are not the super destructive beasts they were earlier when thrashing the tropics.  Typhoons up beyond Kyushu/Shikoku may mess with travel infrastructure, but they are rarely lethal forces of nature.  We have a list of transportation services pinned to the top of the sub.  If you are unsure whether your flight/train/trolley/go-kart/donkey ride will be affected, please consult your travel provider, which may be in this list.  For those taking ferries or other marine transport, no sensible operator is going to see 15 foot waves and think, “Yeah, I can make it to Okinawa today.”  

Edit: Why in the name of all that's crazy do the pictures and movies flake out? They just disappear. WTH, Reddit?

  Unsettled weather patterns continue across much of Japan today as rain covers a large swath of the country south and west of a line from Hitachi to Nagaoka on down to Kansai and on into Shikoku.  Additional scattered showers are moving along western Honshu and Kyushu.

  A low pressure system is moving across the Sea of Japan today, spawning a couple of fronts which are triggering our rainy weather.  The setup is a classical rainy season pattern for central Japan at this time of year.  The weather will move over the country through the evening, bringing consist rain for the remainder of today and on into tomorrow morning.  Areas of Hokuriku, in particular, may see heavy to severe local rain accumulations as the system moves through.

Tonight's expected rain profile as the low moves across the country.

Radar snap of where the rain is falling as of 16:30 this afternoon.

The Himawari image, too, shows a country shrouded in clouds.

Initial track forecast of the newly-delveoped T7

  After the system moves over Japan on Sunday, we can expect unsettled conditions to continue pretty much nationwide.  As we head into the new week, the Japan’s weather will be dominated by mostly cloudy skies with some local showers popping up here and there.  As erratic as the atmosphere over the nation will be for the next few days, it is hard to pinpoint, but in the midst of the clouds, some areas may get a bit of sun peeking through the clouds from time to time, but the safer bet is to expect cloudy conditions with a consistent chance of rain.

  Typhoon 7 (aka, “Mekkhala”), too, has formed in the Philippine Sea.  Sitting at a position of 14.4 degrees north and 136.9 degrees east as of 15:00 today, the storm is generating sustained winds of 80kph with gusts of up to 108kph.  T7 is heading west-northwest at a speed of around 15kph and is expected to maintain that course and speed for the next couple of days, strengthening as is drifts toward Taiwan.  The storm is forecast to hit peak strength late on the 23rd, just as it begins to pivot and recurve north - northeastward toward Japan.  T7 will already be weakening as it begins to start messing with Okinawa’s weather from the evening of the 25th through the 26th as it hits strong winds aloft and moves into cooler sea surface temperatures.  Still a sizable storm, T7 will then track along a very similar path as T6 did earlier this month, and will bring rain and wind to the Pacific coast from the 26th through the 28th.  There is a chance, according to the ECMWF (European) model, that T7 could combine with another low coming in off the Korean Peninsula around the 26th, and that could augment the rain and wind profile of the typhoon as it moves along the Pacific Coast.

  Still, the approach of T7 is still a good five to six days away and we need to get a little closer to get more accurate readings of what to expect.  Safe to say T7 will swing by close to the country, but we need to wait awhile before we can how much rain will come and where.

Peace out everyone, and enjoy your Saturday.

Back in the 1980s, I remember a local weather forecast that gave this exact quote. I'm guessing I was the only one listening because it didn't seem to register with anyone else, not even in the studio. Sounds ridiculous.

Except this seemingly paradoxical sentence also is a fair summary of the skies over Japan for the next two days or so.

This morning satellite image. 15 Jun 2026; 08:00 JST

Same image, but with fronts overlaid. Can you tell I have almost no artistic talent? Pretty obvious, eh?

National radar this morning showed a large area of precipitation associated with the offshore low leading out into the Pacific. But, more scattered rain is in the forecast.

  Many of you in Kanto woke up to a band of showers, but that was associated with a low moving off the Pacific Coast and they had moved offshore largely by 10am.  By 10:30, all of Japan was pretty rainless, except for Okinawa, which is getting a fair amount of wet stuff thanks to a stalled rainy season front sitting right over the islands.  For the rest of the day and into to tomorrow, no system-related precipitation is expected to fall in the main islands, but there is a risk of pop-ups this afternoon nationwide, and the humid air you feel today may fuel those pop-ups as we get daytime heating under way.  The chance for these sudden thunderstorms is higher in the north, from Tohoku on up to Hokkaido, and lesser in points south and west, but still overall elevated across the country.

  We do have a lot of systems moving through the area, mostly in a train going from Taiwan and Asian mainland down southwest, moving northeast over Japan.  This is going to make our weather very unstable for the period.  For the next two days, through Wednesday evening (June 17), we can expect fair to cloudy skies over the country.  Yeah, that’s pretty broad, isn’t it?  Doesn’t exactly qualify as a pinpoint forecast, but really, with the unstable atmosphere we have over east Asia right now, it’s also accurate.  Sunny skies, then some clouds will move in, then they’ll move out…that sort of thing.

  No major rain threats through Tuesday evening, aside from today’s pop-up risks.  With another moderate low system moving through, parts of the Pacific coast may see some rain showers on Wednesday into Thursday, with pockets of locally heavy rain possible.

  Temperatures through Wednesday will be capped in the upper 20s nationwide, with the possible exception of Kyushu, which may breach 30 in some areas.

More updates later. We do have a couple of sizable systems lining up to move over the country later in the week and over the weekend, but things are too turbulent to make an accurate forecast right now. By midweek, I should get some clarity in this and we can make a better call. Have a most excellent week, everyone.

If you are unfamiliar with the term, "pop-up thunderstorms" (known locally as ゲリラ豪雨 guerrilla gou) are sudden, highly localized, potentially severe, storm cells that bloom rapidly in humid, unsettled skies. While they typically dissipate within a couple of hours, under the right conditions they can stall and last for 6 to 8 hours. The rainfall is intensely focused; one town might face a severe deluge while the next village over stays completely dry. They frequently bring frequent lightning, thunder, and in exceptionally rare cases, isolated tornadoes. Hail (雹、ひょう), can also generate quickly, thanks to the violent up and downdrafts present in a storm.

[Fun Project: Get a hailstone and quickly cut in open to find out how many times it went up and down in the thunderhead before falling to earth!]

Tomorrow's pop-up thunderstorm risk map. Purple represents highest risk. [Data from WeatherNews]

If you are new to the world of pop-up thunderstorms, here is a pretty typical photo taken during a downpour in Osaka last August. They are very local and can be very heavy.

Heat stress levels will be moderate tomorrow, due more from humidity than temperature, with Nagoya and Hiroshima running the highest risks. [Image from Genki.jp]

Tomorrow's Risk (When & Where): Atmospheric conditions tomorrow will be ripe for these sudden developments across the northern half of Japan. An elevated risk exists from Kansai up through northern Tohoku, with higher chances from Kanto on north, primarily between the hours of 11:00 to 16:00.  If you are outdoors, especially near rivers, streams, or low-lying areas, keep a close eye on the sky and seek shelter immediately if you notice dark, threatening clouds.

Heat & Humidity Notice: Yeah, it's getting to be that time of year again. Meanwhile, although maximum temperatures nationwide will come in under 30°C (with areas around Nagoya potentially breaching the 30°C mark), high humidity will elevate the risk of heat stress. All areas of Japan will be under a guarded or cautionary heat stress level tomorrow (as opposed to higher caution or danger levels). If you plan to be outside for extended periods, please take regular breaks to rest and cool off.

https://preview.redd.it/l9tnmtyzif6h1.png?width=1417&format=png&auto=webp&s=b7ad6611101d69f3b5e5fb6d7c024c8b3d313450

Taken at 18:00, JST today, 10 June.
This is a seriously beautiful image.

  As another post today noted, it has been kind of a cool June, especially for Tokyo and points north.  Great news, but...what’s going on? What's driving this?

  Simple answer is that the rainy season is working the way it’s supposed to.  This is the stuff we missed last year.  We have a very clear frontal boundary established between cooler, drier air to the north and warmer, moister tropical air to the south.  Checking this morning’s data showed this split on every metric.  

Frontal system (hand drawn) over surface wind analysis. Very obvious where the front is.

The same front, in yellow, drawn against surface pressure analysis at the same time.

And the front is very visible on satellite imagery

The rain profile, too, tells the same tale.

And the JMA can confirm it.

  The bulk of the Japanese mainland is sitting under the drier northern airmass, under the influence of a kind of weak, but large, high pressure dome sitting over Mongolia.  A low, situated northeast of Hokkaido and moving northeastward is spawning a cold front which is acting as a barrier between the two air masses.  This will hold for the next day or two and bisect Japan’s temperatures cleanly in two.  Take Japan, and imagine drawing a line from Kanazawa down to Tokyo.  Anything north of that line will, for the next couple of days be cooler than normal.  South and west of that line will see warmer temperatures, into the mid 20s.  We will see a warming trend from this weekend but, for now, enjoy what is shaping up to be a very nice and cool June.

The TD (tropical depression) west of Taiwan in the JMA surface analysis, by the way, will unravel soon and won't go anywhere. These things can grow and become typhoons. Not so in this case.

  Skies over Japan will be fair to partly-cloudy over much of the country through Friday, with some areas (mostly in the greater Kanto area and Hokkaido) getting greater than 80% cloud cover.  Friday looks to be especially unstable as a light low moves through the area, bringing an increased chance of rain to central Japan northward.

  The memories of last year’s non-event rainy season and torrid summer aftermath are still fresh in our minds, but that mean that this year will be a repeat?

  Not really. Last year’s late-spring to summer weather was driven mostly by some very unusually strong high pressure domes which set up shop over China much earlier in the year than normal.  That, in turn, knocked other regional systems out of kilter, and interfered with the development of typical rainy season patterns.  In effect, despite having an early and truncated official rainy season, the nation was launched right into summer.  Pop-ups thunderstorms replaced system driven rains, and those China highs played a key role in keeping typhoons away from the country.

  This year, the pattern looks way different and, thankfully, pretty close to normal.  While the rainy season started for Okinawa in early May, most of us in Kyushu, Shikoku and central Honshu on down and west started our tsuyu this past week.  Only Tohoku remains, with a predicted entry into their season of June 20-21.  As things stand now, the rainy season for most areas of Japan is expected to last around normal, plus/minus 4-5 days.  For most of Kanto down to Kyushu, that means lasting until mid-July.

Japan radar profile; 9 June 2026, 08:00 JST

Projected rainfall pattern; 9 June 2026; 17:00 JST

JMA's Rainy Season Tracker. A bit of an eye chart, but you get the idea.

The same chart as above, in a graphic format. Chart by tenki.jp.

https://preview.redd.it/3qthslj4k56h1.png?width=1720&format=png&auto=webp&s=81d9a371632b993bc3fe03545f128150f2e3ca34

https://preview.redd.it/98k4okj4k56h1.png?width=876&format=png&auto=webp&s=8a481c4b49a2ab8e91b2192b49f4a9251a78e2a3

  Rainfall during the rainy season is also expected to be equal or a little above normal.  The maps today are showing a rainy season frontal setup, and radar images from 8am this morning show a line of almost stationary rain stretching along the western Pacific coast.  That system is expected to go nowhere fast as projected rain bands for this afternoon at 17:00 show little change in the morning’s radar picture.

  So, looking at what this means to this week’s forecast, we can expect unsettled skies across the country for the next few days.  At a higher level, pressure patterns across Asia are unsettled, showing a train of lows trailing along the front, on down to Taiwan and beyond.  These shifting lows will help catalyze changeable weather coming our way for the next few days.  In short, we can expect partly-cloudy to cloudy skies for the most part, but the chance of rain is increased nationwide through this week.  For the week, Wednesday looks to be the most stable, with smaller systems beginning to move across the country from Thursday, bringing small, localized showers in their wake.  

  No major systems or storms (like, tropical storm level stuff) predicted to come our way this coming week.  All precipitation will be light to moderate.  Daytime, humidities, though, will increase, bringing with it an increased chance of heat stress.  If you must exert yourself outside this week, please use caution and cool down when you can.  Heat stress can creep up on you, even indoors.

I was messing around with Google Maps earlier today and one rabbit hole led to another. Ultimately wound up in Warrington, England, kind of in between Liverpool and Manchester.
And, yeah, this street name popped up.

https://preview.redd.it/0nsrsjj66v5h1.png?width=1870&format=png&auto=webp&s=538bafd5aa937664230077ada294d4c54880762a