Typhoon Krosa weakened before crossing southern parts of Japan in August 2019.
By HansPeter Roesli (Switzerland)
Typhoon Krosa developed from a tropical storm and started to be tracked while it was in the Philippine Sea on 5 August. It reached typhoon strength between 7 August 18:00 UTC and 10 August 06:00 UTC, jumping briefly to Category-3 equivalent on 8 August, while still being over open seas.
It then moved towards southern Japan as a tropical storm, crossing the country on 15 August, before dissolving over the Sea of Japan.
The animation (Figure 2) documents Krosa’s path between 6 and 15 August, tracked by six-hourly positions given as dots, coloured from blue (tropical depression/storm) through cyan and brown to orange (Category 3 typhoon).
Figure 2: Animation of Himawari-8 visible (00 UTC frames) and infrared (12 UTC frames), 06 Aug 00:00 UTC–16 Aug 00:00 UTC
The track is overlaid with 12-hourly interleaved images from VIS0.64 (at 00:00 UTC) and IR10.4 (at 12:00 UTC) of Himawari-8. The other track, west of Krosa, is from Typhoon Lekima that headed almost simultaneously, in similar way, towards the Chinese mainland.
Krosa’s passage through Japan, between 14 August 12:00 UTC and 15 August 12:00 UTC, can be followed in detail in the animation of the IR10.4 band at 2.5 minute time resolution (Figure 3).
Figure 3: Himawari-8 infrared animation, 14 Aug 12:00 UTC–15 Aug 12:00 UTC
Among the many convective events that occurred over the area, one stood out prominently between about 04:00 and 08:00 UTC on 15 August (see red arrow on Figure 1, top right click to expand).
The vigorous dynamics of this particular convective event over open waters, west of the town of Matsuyama, is best seen in a zoomed-in, accelerated animation of both the VIS0.64 and IR10.4 bands (Figure 4). The first upwelling was very fast and took just 10 minutes to reach the top of the troposphere. Subsequently, new convective towers emerged below the new cloud deck that manifested in protruding tops or gravity waves in the VIS0.4 images, and as darker red (colder) spots in the IR10.4.
Figure 4: Himawari-8 visble (left) and infrared (right) animation, 15 Aug 04:30–06:10 UTC
Previous cases studies
Super Typhoon Lekima (4 August 2019)