Evolution of a Typhoon-Like Subtropical Low Causing Severe Weather over the Kanto Area on 13 October 2003

抄録

The purpose of this article is to document genesis, development and dissipation of a subsynoptic-scale typhoon-like cyclone, that caused severe weather on 13 October 2003, over the eastern part of the Kanto area. In this documentation, practically all available data obtained operationally by the Japan Meteorological Agency are used.
The subtropical low of interest formed initially as a mesoscale vortex at 0000UTC 8 October over the ocean near Okinawa Island (∼26°N, 128°E), where the western end of a quasi-stationary polar front was located. The genesis region is characterized by a weak baroclinicity, and nearly saturated low-level atmosphere, with a negative Showalter Stability Index. Several mesoscale convective systems developed prior to the formation of the subtropical low in the genesis region. It is inferred that diabatic heating, by the release of latent heat in deep convection helped spin up pre-existing relative vorticity associated with the quasi-stationary polar front. In addition, an upper-level short wave trough spawned a cut-off low over the region, helping the vortex to develop into the subtropical low. When matured ∼50 h later, the subtropical low exhibited remarkable axisymmetry in the wind and thermal structures, with the diameter of l00∼200 km. The cloud pattern also displayed a cloud-free eye-like structure. After it traveled slowly northwards for four days, the subtropical low was overtaken by a synoptic scale trough, and underwent the processes known as the extratropical transition of a typhoon, while it moved towards the east.
Finally, briefly discussed are similarities and dissimilarities between the present subtropical low, and hurricane-like subtropical cyclones that develop in other regions of the globe, such as the Mediterranean Sea and the central/eastern Pacific Ocean.