r/japanweather

Two of us, Nov 8–26. Tokyo → Nikko → Kawaguchiko → Hakone → Takayama → Kyoto → Osaka → Fukuoka (Takachiho day trip) → Hiroshima/Miyajima → Tokyo. All booked, changing dates will be really tough.

Japan looks rough from outside with the floods and I'm worried about the weather in November. Let me know what I should do, if its going to be worse, I can still try to cancel my trip :(

A summary of the typhoon situation as things sit this morning, 8 October.
Typhoon 27 is in the record books, but what's up with the other two cyclones in the western Pacific?

And this is legit physics, not science fiction.

There are three typhoons out the Pacific now.  Typhoon 27 (“Choi-Wan”) is one of the strongest storms we have seen in the Pacific so far this season.  Typhoon 28, which also goes by its former name of Nolo, is a trans-Pacific traveler which started in the waters off Mexico and has made the rare journey to our side of the world.  Typhoon 29 (“Koguma”) is an up-and-coming new storm with the potential to grow significantly in the next 48 hours.  

 They are all headed toward us, yet, the way surrounding systems are set up, it looks we have a very good chance to get lucky and avoid a direct hit from any of them.  

Family portrait, T27, T28 and T29. Sat movie from 4 Oct 22:00 - 6 Oct 08:00

Surface Pressure prediction, 8 Oct, 06:00 JST (Data as of 6 Oct, 06:00)

  First off, the stats of each storm, as of this morning’s 6:00 JMA data run:

  Typhoon 27  Location: 29.1N, 145.6E, about 800km SE of Tokyo, moving N at 20kph.  Central core pressure of 950hPa.  Sustained winds over water of 150kph, gusts of 210kph.  Gale force winds extend out 850km east, and 560km west of the storm.
  T27 is forecast to continue moving northward, pivoting to a northeast bearing by the morning of 7 Oct, and the storm will continue to edge away from the Japanese mainland.  While there will be no landfall from T27, coastal areas of Chiba and Ibaraki prefecture may get some gusts as an effect of the extreme outer wind bands of the storm.  

  Typhoon 28  Location: 25.7N, 173.9E, about 3,300km ESE of Tokyo, moving W at 25kph.  Central core pressure of 960hPa.  Sustained winds over water of 165kph, gusts of 240kph.  The first tropical cyclone to cross the International Date Line since Dora in 2023.  This remarkable storm first formed as a disturbance about 1,000 SW of Baja California in the eastern Pacific Ocean.  It strengthened, became a hurricane, moved west toward Hawaii and caused some flooding on the Big Island around 25-26 Sep, and then continued on its long ocean voyage, transiting the IDL yesterday (5 Oct) around 9:00, JST, where it became designated as Typhoon 28.  While still a very strong storm, T28 has passed its peak, and will gradually degrade as it moves west, encountering additional wind shear.

  For all its efforts, though, T28 will not make it to Japan, forecast to turn north about 1,000 or km offshore and move into colder waters.

  Typhoon 29  Location: 12.8N, 167.4E, about 3,700km SE of Tokyo, moving NNW at around 5-10kph.  Central core pressure of 1000hPa, with sustained winds of 65kph.  This is the new entry into the mix, just graduating to JMA typhoon status yesterday.  It is still a disorganized storm with no eye and no defined cyclonic movement on satellite.  It is projected to strengthen and mature over the next 48 hours, maintaining movement northwest and, by Sunday, 11 Oct, it may threaten the Mariana Islands, although its exact course through the tropics at this point is far from certain.  

  A little on the mechanics of what's going on here, and this will get a little deep, but stay with me: Checking the ECMWF chart Thursday, 8 Oct @ 06:00 JST, and you will probably go straight to that strong high sitting over the Korean Peninsula, with a long ridge of high pressure stretching east across Japan. While it is tempting to say "Oi, there's the shield keeping the typhoons away!” keep in mind that surface highs don't steer typhoons.

  Storms are carried along by a "deep-layer" flow through the atmosphere, mainly the subtropical ridge and the troughs in the mid-latitude westerlies. The surface map just shows us where that ridge lives.  Think of it like this: a typhoon is a tower of rotating air reaching well up into the atmosphere, and it gets carried along by the average wind through that whole tower, mostly set by large high-pressure areas (commonly called, “ridges”) and the jet stream-level troughs, operating about 10,000m or so up. The surface map shows only our ground-level view of the story.  It gets pushed along, much as a tall tree leans with the average wind rather than just the breeze at its roots.

  So what does the ridge actually do? T27 is the easy one. It's already pivoting up north, steered by the westerlies, and by Thursday, it should well away Japan, moving up north.  Nothing to write home about here.

  While current data suggest that T28 and T29 will not make landfall, to be fair, they are still way out at sea and a lot can change in the meantime.  It will be between 3-4 days before we can get a definitive read on them.  T28 and T29 both sit on the southern flank of the ridge, and that's the key. Storms riding south of a ridge get pushed westward and they only turn poleward when they reach the ridge's western edge or a competing trough breaks it down.

  At this moment, most major models agree on this assessment for T28 (Nolo): a building ridge to its northwest keeps it tracking generally west until about 72 hours out, then it curves northwest as it rounds the ridge axis, with the big question being how far west each storm travels before it turns.  It will turn and head north; it’s just a matter of when.

 And that's where the uncertainty lies with T28 and T29 at the moment. A stronger ride or one which spans out further east than forecast means a longer westward run and a turn closer to Japan.  On the other hand, a trough arriving sooner means an earlier turn and a safe pass out at sea.  Models right now, although in general agreement on the course of the storms, disagree on the timing.  NAVGEM and JGSM show a sharp pivot north, while GFS, ECMWF and the ensembles curve wider and slower.  T29 carries the widest spread: some runs have it passing east of Honshu, others bring it toward the Izu Islands.  We’ll get a firm grip on these tracks in a few days.

  Bottom line: The high moving over the Asian mainland now will bestow gorgeous weather upon Japan this week, and it looks unlikely that we will get any landfall from all the storms out at sea now.  That said, while the data certainly looks that way as things sit today, things can change. Keep your eyes on the skies.

  Good morning.  First off, I was out almost all last week on day job matters, so sorry about that.  Some folks in the head office overseas decided they needed some stuff from Japan due immediately if not sooner, and that pretty much nuked my week.  With that mess done, now I have a bit of time to see what’s happening in the skies over Japan

  Trying to catch up on all that’s gone on in the weather.  I was able to look outside once or twice and noticed the rain had stopped.  The tenacious autumn rain front (秋雨前線) that messed with the weather here for the past four weeks has finally let up, leaving behind a very saturated September. Tokyo ran up a streak of 36 consecutive days with measurable rain, a record which stood since 2019 that nobody really wanted to beat. 

T27 24 hr Satellite Loop: 3 Oct 22:00 - 4 Oct 22:00

The JMA's read on T27 as of 9am this morning

JMA's surface analysis of the weather buzz in and around Japan.

And, yes, we do have two others out there. The jury is still out on whether or not they will be players in our weather scene.

Glamor shot of T27. 5 Oct, 09:30 JST

  Can October be a bit better?  Certainly, we have a chance.  A weak low pressure system trailing a front is working its way through the northern parts of the Sea of Japan and on into Hokkaido today and tomorrow, so we're not entirely clear yet. Cloud covers much of the nation this morning, but there is sunshine across parts of western Kyushu, the Sea of Japan coast, Hokkaido and some dots of sun in Okinawa.

Tuesday's front will bring rain from Hokkaido through the Sea of Japan coast of Tohoku and Hokuriku, along with a chance of locally heavy short downpours and gusty winds.  Eastern Kanto, specifically the along the seaboard of Chiba and Ibaraki, could see some spotty rain as well.

After that, a high will take over and begin to dominate the country’s weather.  Building in from the west, Japan should see broad sunshine with sunny to partly-cloudy skies nationwide from Wednesday onward.  Temperatures will run normal to a bit above normal for early October, warming further toward the weekend.

Guys, we've got sunshine in store.  Y’all remember sunshine, right?  You know, the hot ball in the sky?  Ring a bell?

Wednesday will still have some clouds hanging around on the Sea of Japan coast, but from Thursday it's going to be splendid, and the upcoming three-day weekend (10-12 Oct) is shaping up very nicely indeed, much different than the half sloppy/half really humid Silver Week we recently had.

But first, we need to get through T27. Typhoon 27 (aka, “Choi-wan”) is a very powerful storm, and we should take a moment to whisper a little prayer of thanks to whatever deity or celestial weather being you worship [or pass a beer and pizza to your favorite weather sub!] that this brute of a system will stay well offshore.  Without employing my usual profanity-laced metaphors, Typhoon 27 is a monster of a storm, one of the strongest typhoons to pop up so far this season.  As of JMA’s 6:00 data run, it was near 24.8N 146.6E, roughly 1,400km SSE of Tokyo, moving north-northwest at 20kph. Central pressure is 925 hPa, with sustained winds over water of about 180kph, and gusts to a breathtaking 250kph.  It is a large, powerful storm.  The area of storm force winds (defined by the JMA as that parcel of ocean where sustained winds hit 90kph or greater) extends 220km to the east and 165km to the west of center, while the gale force winds (54kph +) reach out in a lopsided 850km to the east and 560km to the west of storm center. Satellite imagery shows a clear, beautiful, well-defined eye, the mark of a mature storm.

T27 is peaking today, with the 925 hPa mark reached around 3am.  The path downward from here will be slow, but definite.  The storm should stay "very strong" (非常に強い、ひじょうにつよい) through Tuesday, then ease to "strong" and turn extratropical around the 7-8 Oct.

The good news here is the track.  All major models, including the JTWC, JMA and ECMWF has the T27 continuing north near the Ogasawara Islands, then bending northeast keeping the storm well out over the open Pacific.  The tempest, staying far offshore, well east of the Japanese islands, means no landfall.  And, for a rain-and-storm-weary country, we can take solace in that.

There will be some impact, however, in the form of surf and winds.  Waves up to 8m are forecast for Ogasawara through Tuesday, around 5m for the Izu Islands, and rough seas will reach the Pacific coast of Kanto and Tohoku from Tuesday into Wednesday.  Winds too will pick up over the Izu Islands and Kanto on Tuesday and Pacific Tohoku on Wednesday, with forecasts estimating up to 40kph winds along the coast.  Stay away from the coast and skip the fishing.  Surfers, on the other hand, well, you guys are a different breed.  Go do what you do best if you want.  I wouldn’t and you shouldn’t, but, surfers gonna do the nami thing.

Any rain on the mainland Tuesday will come from the low and trailing front system and not directly from the typhoon.

Kanto will see a warm spike Tuesday as the typhoon's circulation pulls warm air north, standard for post-typhoon patterns, but still surprising as T27 has the power to bring in all this tropical air while still being so remote.  Highs in Kanto and parts of coastal Tohoku should jump from today's 20–21c to somewhere in the 24–29c range, and then ease back toward normal by Wednesday–Thursday.

Beyond the Kanto spike, highs will be uneven across the country. Expect around 30c in Kagoshima and Naha, high 20s in Fukuoka, and much cooler air in Hokkaido and inland Tohoku, where lows drop into single digits. Under the migratory high, temperatures edge upward toward the weekend, with Kanto commonly topping 25c.

And, yes, we do have a couple of other little squirrels darting around in the Pacific now. We'll keep an eye on those and see if they're worth reporting on.

Have a great week, everyone.