Convection in the major part of Typhoon Yancy (T9313) which moved westward during the early gradual developing stage over the northwestern Pacific near (19N,129E) during 30 August to 1 September 1993 was analyzed using the radar data, maritime weather and upper air observation data obtained on board a research vessel Keifu Maru, Japan Meteorological Agency near the center of Yancy. Recently available satellites data were also used in the analysis. Cell echo tracking winds (CETwinds) were used to supplement the wind data near the 700 hPa winds.
At the beginning of the early developing stage, lower-level cyclonic circulation (LLCC) of 1500 km scale associated with a cloud system in its southwest quadrant already existed. During the early developing stage, this in-concentric cloud and LLCC structure of Yancy was transformed to concentric one through the formation of 'CDO'. After that, rapid development of LLCC started. During the early developing stage, convection was organized in variable mesoscale (100-500 km) precipitation features (MPFs) such as large (400 km) echo system (LES), line systems transversal or longitudinal to lower-level circulation, long lasting mesoscale intense convective area (MICA), and spiral band systems. Center of LLCC approached as close as 80 km to the north of the ship during the westward movement of Yancy.
The early developing process of Yancy was investigated on mesoscale and divided into four sub-stages based on the configurations of the MPFs. In the initial sub-stage, LES with scattered convective echoes was organized in the southwest quadrant of LLCC , over which a round cloud system appeared. In the second sub-stage, MICA was formed and maintained around the northwestern edge of the LES for nine hours beneath a central part of central dense overcast ('CDO' ) in the round cloud system. LLCC appeared to be intensified on 500 km scale after the formation of MICA. In the third sub-stage, LES evolved into comma-shaped spiral band with length over 500 km and another spiral band was formed in the intense cyclonic circulation. The cloud system also evolved from round to comma shape and 'CDO' was dissipated. In the final sub-stage, northern head of the comma-shaped system was encircling the LLCC center. Curvature of spiral bands was increased and a new near-circular spiral band emerged in the intensified LLCC.
LES and MICA constructed a kernel structure of Yancy on the early developing process. In the MICA, echo top height attained to 16 km, intense convective echoes tilted eastward with height, and moderate echoes spread to the north of the intense echoes. The MICA possessed a three dimensionally well organized structure for long lasting intense convection. Such that, surface warm and moist (high 0e) west-northwesterly and west-southwesterly inflow converged around northwest periphery of MICA and met south-southwesterly flow of low 0e prevailed in a heavy rain area in MICA, which might maintain intense and long lasting upward motion in the convection. Total rainfall on the ship within MICA attained to 147 mm for 6 hours.
The MICA was a mesoscale precipitation entity of the 'CDO' which appeared to proceed intensification of LLCC on 500 km scale. Some aspects of the MPFs correspond well to those of numerically simulated mesoscale convection during Tropical Cyclone development in Yamasaki (1983, 1986).