Simulated Changes in Storm Morphology Associated with a Sea-Breeze Airmass

The central east coast of Australia is frequently impacted by large hail and damaging winds associated with severe convective storms, with individual events recording damages exceeding $1 billion AUD. These storms present a significant challenge for forecasting due to their development in seemingly marginal environments. They have often been observed to intensify upon approaching the coast, with case studies and climatological analysis indicating that interactions with the sea breeze are key to this process. The relative importance of the additional lifting and vorticity along the sea-breeze front compared to the change to a cooler, moister airmass with stronger low-level shear behind the sea-breeze front has yet to be investigated. To understand the effect of the sea-breeze airmass on storm morphology, a storm was simulated in an environment similar to the 27 November 2014 Brisbane hailstorm. The base-state substitution (BSS) modeling technique was utilized to introduce the sea-breeze airmass following initial storm development. Compared to a simulation without BSS, the storm was longer lived and more intense, ultimately developing into a supercell. Separately simulating the changes in the thermodynamic and wind fields showed that the enhanced storm longevity and intensity were primarily due to the latter. A closer balance between the low-level environmental winds and the storm’s cold pool, produced a deeper, more vertically erect updraft while allowing the storm to continue ingesting warm, potentially buoyant air ahead of the gust front. At the same time, increased low-level shear resulted in storm relative helicity that was sufficient for rotation to develop and the storm to transition to a supercell.