High-Altitude Platforms (HAP) could offer an interesting alternative to both ground- and space-borne instruments when neither configuration offers an optimal solution. Specifically, for Doppler radar measurement of meteorological targets, ground-based radars are incredibly useful but limited in their area of deployment and space-based instruments providing a 3D sampling are particularly challenging to design if Doppler measurement is requested. Stratospheric balloons could offer some very interesting possibilities to build a reference database of the dynamical properties of convective clouds. The idea of using stratospheric balloons is developing, to make pseudo-satellite platforms. In the case of radar, this is a particularly interesting prospect because a platform at an altitude of 20 km offers performances close to that of a ground system. Likewise, the possible speed of displacement of the platform is in orders of magnitude close to the sought-after Doppler shifts. The main disadvantage of drifting balloons is their random trajectory (to a certain extent) and he fact that in the upper part of the tropopause or in the lower stratosphere, the currents are rather divergent from the convective cores which could tend to move the instrument away from the most intense events. In the tropics, an altitude of 20 km is probably not optimal since deep convective systems will influence the trajectory due to the divergence at the top of the towers which will repel the balloon. However, a balloon flying at an altitude of 20 km will still be able to observe significant convective activity. Two concepts will be presented. The first one is a radar on an Open Stratospheric Balloons (OSB) in order to follow events (squall line type) over short durations (35h max). The free-drifting balloons are a first step meant to strengthen our expertise and develop a prototype of a radar. The ultimate goal is to be ready when a blimp-type stratospheric system is ready to fly. The latter would then offer some outstanding possibilities to complement both ground-based and satellite observation. Early studies on trajectories of free drifting balloon in the Tropics and the associated link budget will be presented.