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Friday, August 16, 2019, 21:00 CEST

Tropical Cyclone
August 13-16, 2019

Satellite image (visible) from LEKIMA (western) and KROSA (eastern)
August 08, 06 UTC
Source: NICT

KROSA was the fourteenth named storm of the 2019 Pazific Typhoon Season. With a maximum wind speed of 185 kph, it was ranked as Category 3 typhoon, but after weakening it made landfall in Japan as Tropical Storm.

Development and trajectory

The cyclone developed from a depression near Mariana Island on 05 August. Already on 06 August the system reached tropical storm stuts and received the name KROSA. On 08 August it reached Typhoon strength before it rapidly intensified and reached its maximum strength within the same day. On 08 August at 12 UTC, Category 3 Typhoon had wind speeds of 185 kph and gusts of up to 215 kph. The core pressure decreased by 40 hPa within 12 hours (from 07.08. 15 UTC until 08.08. 03 UTC). The minimum core pressure of KROSA was 950 hPa.

KROSAs Trajecotory from 05 August until 16 August Wunderground

From 07 to 11 August the typhoon was almost stationary. In the water masses beneath the cyclone, cold water from low layers was whirled due to the high wind speeds and the resulting waves therefrom. This led to deceasing sea surface temperatures, so that the oceanic water in this area could no longer provide enough energy to maintain the intensity of the typhoon.

Soil pressure and ground observations, 13.08. until 16.08., 00 UTC: source Japan Meteorological Agency

As a result, KROSA weakened into a tropical storm. It then restarted to move northwest again at moderate speed of about 20 kph, with its core pressure and mean wind speed remaining almost constant over a period of multiple days (965 hPa and 90-100 kph). On 15 August at about 03 UTC, KROSA made a landfall as a tropical storm in the Japanese prefecture of Kochi. Its trajectory led further north across the prefectures of Ehime, Hiroshima and Shimane before the system moved back to the ocean at 09 UTC at the same day. Over the Japanese sea, the storm weakened more and more, but also in the north of Japan, on the east coast of Korea and partly also in Russia, there was still abundant rainfall.

Sources: NICT and Japan Meteorological Agency

KROSA's lifetime of 246 hours was remarkable considering its only moderate intensity, as the system reached typhoon strength only in 2.5 days. During 7.5 days, the system was classified as a tropical storm and only a few hours as tropical depression.
Another unusual detail was the enormous diameter of the cloudless storm eye, which was up to 80 km at times. The satellite image at the top of the page shows the size of the eye compared to the eye of super typhoon LEKIMA.

Flooding- and landslide risk, 15.08. 11:50 UTC and 16.08. 14:10 UTC, Source: Japan Meteorological Agency


Since the classification of tropical storms is only based on core pressure data and mean wind speeds, this classification gives very little information about the amount of precipitable water. As can be seen in the satellite and radar film, tropical storm KROSA caused convective clouds and heavy precipitation over a large area.
The radar film also shows how precipitation drains off on the southern hillsides of the Japanese mountains. The rainfall amounts on the island Shikoku, in the prefectures Wakajama, Nara and Mie and south of the Hida Mountains is much higher than in other parts of the country.

Hourly precipitation (observation) from 15 August, 11 UTC in Shikoku and the southern coast of Honshu, Source: Japan Meteorological Agency

The table below shows an overview of 24 h precipitation in the affected areas. It is worth a note that tropical storm KROSA also caused rainfall of more than 100 mm/24h in parts of China and Russia.

Location 24 h Precipitation
amount in mm
Yakusima (JP)

Ryujin (JP)
Sakihama (JP)
Hikigawa (JP)
Kawabe (JP)
Owase (Japan) (JP)
Muroto-Misaki (JP)
Pos'Et (RU)
Murotomisaki (JP)
Yanji (CN)

Karurusu (JP)
Morino (JP)
Noboribetsu (JP)
Nakakineusu (JP)





Data source: Source: Japan Meteorological Agency, Ogimet.

Text: FS
August 16, 2019

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