Typhoon No. 15, known internationally as Chan-hon, weakened to a tropical depression in the Sea of Japan by 9 a.m. JST on Wednesday [1, 2].
The degradation of the storm marks the end of a high-alert period for central and eastern Japan, where the system brought significant wind and rain.
The storm made landfall in Ibaraki Prefecture on the night of Aug. 11 [1]. As it moved across Honshu, the system interacted with moist air and landmasses, causing it to lose the intensity required to be classified as a tropical storm [1, 5].
Data from Aug. 11 at 9 a.m. JST showed the system had a central pressure of 985 hPa [3]. During that period, maximum sustained winds near the center were recorded at 23 m/s, with maximum gusts reaching 35 m/s [3]. The storm was moving at a forward speed of approximately 30 km per hour [3].
Reports on the exact timing of the storm's weakening vary among meteorological sources. Some reports indicated the transition to a tropical depression occurred by 9 a.m. JST on Aug. 12 [1, 2]. Other forecasts had previously suggested the system would reach tropical depression status by 9 a.m. JST on Aug. 13 as it moved toward the coast of San-in [3].
Local authorities in Ibaraki and across Honshu monitored the system as it crossed the mainland. The weakening occurred as the storm entered the Sea of Japan, effectively ending its threat as an organized typhoon [1, 2].
“Typhoon No. 15 weakened to a tropical depression in the Sea of Japan.”
The transition of Typhoon Chan-hon into a tropical depression signifies a loss of the storm's structured core, reducing the risk of catastrophic wind damage. However, the remnants of such systems often continue to carry significant moisture, which can lead to localized heavy rainfall and flooding even after the wind speeds drop below typhoon thresholds.
