The coming Japanese snow season 2019-2020 Weather

It's way early, and sort of the first day of summer in Japan (1st June). So why such an early "coming snow season" thread?

Earlier in the week, a heatwave ended, after about a week of 30C+ temperatures around Tokyo.
It was unusual because it was still May, still spring. But last Sunday, 513 of JMA's 926 weather stations recorded temperatures > 30C degrees, and 53 recorded > 35C.

Strangely, the hottest place was Hokkaido, where May mean max temperatures are around 17C degrees.
In the town of Saroma, on Hokkaido's far NE coast, the temperature got up to 39.5C degrees. It was the hottest temperature ever recorded in Hokkaido, and the hottest May temperature ever recorded anywhere in Japan, in May.
I'm still not sure why this particular location was so hot. There was a WSW wind blowing off the hot Asian mainland, but there was 500km of the Sea of Japan, to moderate those hot winds. There was high pressure the preceding days, but there seemingly should not be enough heat so early in the year.
The temperatures have dropped back since then. Saroma's max yesterday was 24.6C

 

We had the July heatwave last year, with record hot March, April and July.
Hopefully, the heat is early like last year, but with an early winter season!!

 

So far the Japanese summer has cooler than usual. Rainy season is much more persistent than last year.

 

... and it's been raining a lot in southern Japan.

Since last Friday, seasonal stationary boundary (rainy season) rain front has dumped 1,089.5 mm in Ebino in Miyazaki Prefecture, 901 mm in Kanoya, Kagoshima Prefecture, and 611.5 mm in Yunomae, Kumamoto Prefecture.

In the city of Soo, rescuers found a missing woman in her 80s buried in a house that was engulfed by a landslide. She was later confirmed dead at the scene, bringing the total number of deaths from the heavy rain to two. The city saw a record 421 millimeters of rain on Wednesday — the highest since data was first recorded in 1977.

At its peak, evacuation orders were issued for about 1.1 million people in Kagoshima and Miyazaki Prefectures around 4 a.m. Thursday.

All evacuation orders and advisories in Miyazaki Prefecture were lifted by 11 a.m. yesterday, according to the prefectural government. However, the Kagoshima Prefectural Government urged residents to keep exercising caution Thursday afternoon, citing fear of landslides.

 

You can see where the "rainy season" is located on this map, where the green line is located.



Every year in June/July, this stationary boundary moves across Japan, bringing rain. It's starts off near the Philippines in around April and slowly moves north.
To the north of the boundary, the air is cooler and drier, south of the boundary, it's warmer and more humid. The collision of warm and cool air causes the rain along either side of the boundary.


This is usually (and has been this year) responsible for the heavy rain in China.

Once it hits the temperate zone in north Honshu, it dissipates, due to the cooler air and the prevalence of northern low pressure.
Once the boundary moves north, central & southern Japan moves into the normal summer heat and humidity (day time low to mid 30s C. It usually takes 2-3 weeks.

It also makes a brief return appearance in September, for about one week, which ushers in the cooler temperatures, in the slide back into the winter season!!

The summer weather in Japan is also very much driven by the Kuroshio Current (pushing in from near the Philippines), which sits at around 26C degrees in summer, moving close to the Pacific coast, extending about half way between Tokyo & Hokkaido. The Tsushima current in the Sea of Japan pushes north, warming to a much lesser extent. The Kuroshio Current comes a lot closer to the coast during the summer.

 

Well, after the start of the rainy season, it's backed off a bit. I HASN'T passed to the north, but has moved back south after a low pressure trough moved through. So this means that the stationary boundary sits to the south of Japan.

It means that we should get a second bout of rainy season before it moves away to the north.
It also means that the cool air still sits over Japan.

The first 9 days of July are normally warm (mean max for the last 20 years 30.5 degrees fro July, and about 27.7 for this time of July), but currently mean max sitting on 25.8

 

Too hard.
We had an unprecedented heatwave in May... I thought it was going to start off June and summer as a terribly hot one.... hasn't been the case so far. Once the stationary boundary moves north, the heat behind it will kick in.
However, that said, the overall heat over Japan has started late, so the summer heat MAY be shorter if early autumn kicks in at the normal time in September.

One other point. I had observed that any August with a Tokyo av max of less than 31C would end up a late and relatively poor follow up snow season. However, 2017 August was 30.4 in Tokyo, but the following season was EARLY and great up until about mid/late Feb 2018.

Last year we had record warm March, April and June. The overall season season afterwards was not early, and warm over Feb/March. I think this might be more significant in the scheme of things.

 

Only a STRONG El Nino seems to have a big impact. (negative)
The ENSO (El Nino Southern Oscillation) outlook is neutral, so no pointers there.

 

Often slightly better, but in any given place, it might be the difference between 11m and 11.5m snowfall.

 

So the mean max for Tokyo for the first half of July (up to 15th) is 24.5C. Mean max for the first half of July should be around 28 degrees.
This year, the mean max for May was 25.3C and 25.8C for June..... it's been downright pleasant here so far!!!!
Looks like the rainy season will finish up around Sunday, and the summer will finally kick in!!!


The start of a series of typhoons will probably blast the stationary boundary away.

 

Regular service will be resumed shortly.....
Rainy season stationary boundary has almost passed to the north:


It was 30.5C degrees in Yokohama yesterday, with a low of 23.8, much more like normal.

 

Absolutely not!!

 

TS Danas has dropped quite bit of rain on Kyushu.
>300mm in 24 hours in some places.
One place (Tosu) has had 187mm in the last 5 hours (80.5 mm in one hour)

 

Sometimes easy to handle, sometimes not.....
Should be hotter and sunnier by Wednesday

 

Incoming:
Tropical Storm Nari

 

Tokyo has had the coolest July since 2007 (Mean max 27.5C. Last year, it was 32.7C). The last week was hot, so before that, it was looking like the coolest July for more than 20 years.
One day into August, mean max for Tokyo: 35.0C
...and humid of course!!

 

TS Fransisco:







161mm of rain in 5 hours in Miyazaki Prefecture.

 

It's been a hot August so far.
Tokyo up to 13th Aug:
Mean max: 34.9 degrees
Mean max: 26.1 degrees

Incoming TS Krosa:

 

It's still a hot August so far.
Tokyo up to 21st Aug:
Mean max: 34.1 degrees
Mean max: 26.1 degrees

Look out for next year's Olympics!!!

However, a slight turn in the weather is on the horizon. The next 7 days have forecasts of 29-31C degrees, and nights dropping to 23-25C (23 towards the end of the week). This is likely to drop the mean max temperature to less than 33C degrees, and overnight lows to about 25.5, which would still be above average for both.

So it seems that the mid summer/late summer drop step is on the horizon. Generally, this happens about the 1st few days in
September, but may happen the last week in August this year.

 

No. It's been 32-34 just about every day from late July.
Tokyo was 33.4 av max for August. However, most years where Tokyo had an August av max >33C, has been had good winter snow

 

Well, huge thunderstorms here in Yokohama.
My smartphone has been hitting me with emergency alerts for local evacuations. It's a hilly area with cliffs. It was WAY heavier a few km south of me, and it was VERY slow moving. Only 31.5mm at my place, but it will be interesting to find out how much fell nearby.

From JMA:
Yokohama-shi
Heavy rain (Ground-loosening, Inundation)
Flood
Thunderstorm

 

Ok, so Cat 1 typhoon Faxai came through in a direct hit on the greater Tokyo area. In Yokohama, where I live, the maximum gust was 150.5kph, and 150mm in 5 hours (including 66mm in one hour), and a little more either side.
On the Izu peninsular to the west, at Amagisan, there was 472mm in 12 hours, including 183.5mm in 2 hours.
The eye it the storm passed about 10km to the east of my place.

Fortunately (or unfortunately), I was away in Texas!!!!

 

The step change in central Japan looks like arriving in the next couple of days.

So far in September, Tokyo has a mean max temperature of 32.0C degrees, and a mean min of 24.0 (both well above average).
The next week of highs forecast for Tokyo are 27-29C degrees after Thursday, and lows 21-23 degrees.

There's no sign of the stationary boundary yet, that kicks in later in September, producing about 1 week of wet weather before the next step change with cooler temperatures behind the boundary. This period before and after is also the typhoon season.

Once that happens, the ski shop area in Tokyo will start hauling out the snow gear to the shop fronts, relegating the surf & hiking gear to the back, and the slippery slide to the winter snow approaches!!!!

This period of weather step change I like to call the late summer /early autumn transition.
The next period is what I call early autumn. (mid Sep to early Oct)

Then (in Tokyo), the weather step changes:
- Early autumn: Mid Sep to early Oct
- Early/mid autumn: Early Oct to end Oct
- Mid autumn: Early Nov to end Nov (first snows in central Japan happen in the last half of Nov)
- Late autumn: Early to mid Dec (about the time the Japanese maples reach their peak colour in Tokyo)
- Early winter: Mid Dec - early Jan (the first big dumps of snow in central Japan around 15-20th Dec)
- Mid winter: 2nd week in Jan to end 1st week in Feb. (Consistent snow, and increasing snow pack)
- Mid/Late winter: 2nd week in Feb to end 3rd week in Feb
- Late winter: End 3rd week in Feb to end of Feb/early March
- Early spring: End of Feb/early March to 3rd week in March

 

Well, that's mainly because you were there 3rd & 4th week of Feb!!!