台風Faxaiの上陸前の強度・構造変化

Abstract

A numerical simulation for Typhoon Faxai, which made landfall with the central pressure of 960 hPa in the Kanto region of Japan was conducted using a non-hydrostatic numerical model with a 1 km grid spacing. The simulation successfully simulated the realistic track and intensity of Faxai for 48 h around landfall. The simulated intensity was strong until the time of landfall and the spatial size of the vortex was small. The structure of the simulated Faxai, identified as having an axisymmetric flow field and eyewall, was similar to that of a well-developed tropical cyclone (TC) in the tropics. Around the TC center, the surface latent heat flux was over 300 W m⁻² until landfall, and the vertical wind shear was less than 9 m s⁻¹ between the 1.5 and 12.0 km altitudes, which is relatively weak at midlatitudes. The simulated and best track TC intensities exceeded the maximum potential intensity (MPI) for approximately 12 h before landfall. The present analyses suggest that the strong intensity of Faxai results from favorable environmental conditions and vortex structure.