Depending on sufficient cloud breaks, surface heating over southern counties of England (West Sussex across to Devon) could yield in excess of 500 J/kg CAPE by the afternoon hours in an environment with weak shear but steep mid-level lapse rates. Low-level convergence may aid the development of heavy showers and a few weak thunderstorms in this area, although given the saturated profiles and weak shear, pulse-type mode is most likely (lightning risk 15-20%). Some small hail may be possible, and locally high rainfall totals / localised flooding given the slow movement. Reluctant to issue a SLGT at this stage due to uncertainty over extent of cloud breaks/surface heating - but an expansion to the SLGT may be required if confidence improves.