AM Storms - Melbourne to Osaka Race  by Robin Hewitt

An interesting weather phenomenon is where differential heating during the day between land and sea in the near tropics gives rise to post midnight storms. For anyone curious, here’s how it works.

The land heats rapidly in the clear morning sky and the rising warmed air over it cools with height causing contained moisture to form liquid and even higher to ice. The latent heat released provides temperature to drive the system higher with updraughts that can be up to 10 m/s. So high that jets have to fly around them. The systems can float away from the land in upper atmosphere wind clearing the way for another warm bubble to form and so on. Thus a chain can develop. As the sun sets, the systems begin to cool such that by midnight the updraught has ceased and gravity takes over with drenching rain and squalls.

It has been measured that one cubic metre of air can contain 3.26 mls of water and that therefore a system can hold aloft 3 million tons of water. Having a watch from midnight to 4am means one cops all the drama. A similar process drives a bubble of warm rising air in the ITCZ (Inter Tropical Convergence Zone) whereby the cooling aloft occurs to dump heavy rain about 4pm.

Becalmed in the tropics? Why not take a dip? Cool off?