Severe storm over Japan

By Djordje Gencic (RHMSS), Akihiro Shimizu (JMA), Jochen Kerkmann (EUMETSAT)

The Japan Meteorological Agency (JMA) reported severe weather phenomena such as thunderstorms, heavy rain (rain intensity of 60mm/hr measured by a combination of radar and AWS in the suburb of Tokyo), hail and wind gusts around the area of Tokyo.

This severe weather caused the roads to flood, buildings to be inundated with water, both above and below ground level, water pipes to break, trees to fall, and electricity outages.

Convective storms, passing through Tokyo and the surrounding prefectures (districts), can be seen in the sandwich product imagery (VIS0.6 + Severe convection RGB). This product can be very useful as it nicely combines the high quality texture of the visible channel with important microphysical information from the RGB.

The rising, above-anvil towers seen in the visible imagery, together with the bright yellow signal from Severe Convection RGB, alert us to ongoing, high impact convective weather. This exact scenario can be seen over Tokyo and Kanagawa prefectures in the later part of the sandwich product animation.

Thanks to the Himawari-8 scanning strategy a higher temporal resolution (every 2.5 minutes) is available for the wider Japan area, as opposed to the regular full disc scan of every 10 minutes. It is also worth noting that the spatial resolution differs for channels used in this case, so that, for visible channels it is 1 km, except for VIS 0.6 for which is 500m. For all the infrared (IR) channels it is 2km at SSP.

The conditions were highly favourable for convective development, as an upper level trough passed over the area (Figure 2), 'supplying' high wind shear, which can be clearly seen in zoomed in visible channel imagery (Figures 3 and 4). On the animation low level cumulus clouds can be seen running from the northeast, while higher level clouds and convective cloud tops steer towards the southeast.

With enough available surface lift and upward buoyancy (considering the vast ocean surrounding the area was a moisture source and there was heating of the Kanto plain in July) all the necessary ingredients needed for severe weather were present.

At around 03:30 UTC, the first convective storms appeared northwest of Tokyo. At that moment lots of low level cumulus clouds were present, but only a few of them managed to develop into cumulonimbus (Cbs) and then dissipated after approximately an hour. These clouds were more distinct in the enhanced IR imagery, with the cold Cb tops being better visible than the warmer cumulus cloud tops.

Shortly after the previous storms diminished (04:50 UTC), on their southern edge, much closer to Tokyo centre area, a new system appeared, with very intensive updrafts. This is seen in the Severe Convection RGB (Figure 5) as yellow areas; which coincide with the very cold pixels in the IR imagery, and, finally, with familiar tower shapes in the visible imagery, which confirm that intensive overshooting was occurring.

This overshooting was, with the help of environmental wind shear, much more persistent and after a few images (at around 05:10 UTC) it was obvious that a V-shape storm with an above anvil ice plume had formed, making this storm more intensive than the earlier storm.

Steered by northwestly upper winds the storm moved relatively slowly towards the southeast, directly hitting Kanagawa prefecture. Around 06:00 UTC the storm moved out over areas of Tokyo bay and started dissipating.