Wednesday, March 11, 2009

TC Hamish

Yes, I know it's been a while since I posted anything here. So perhaps the passing-by of a cyclone is a good stimulus to get me going again.

Cyclone Hamish looked for a bit like it might make a direct hit on the north or central Queensland coast, but then veered south-east just in time. A day spent cleaning up the yard, tying the bins to a tree, moving pot plants into the foyer; a nervous day on cyclone warning; gusty but not dangerous winds, squally but patchy rain; a storm surge on top of a 6m tide causing only minor flooding in low-lying parts of Mackay. And then a clearing sky and cooler air in the wake, as the cyclone moved off down the coast.

For a while there Hamish was at category 5, with 300km/h winds near the eye and a central air pressure around 925hPa. That's pretty serious stuff! I did some research and learnt quite a bit about tropical cyclones. Apparently they are normally surrounded by a layer of very high cirrus, the result of the net outflow of damp air from the middle of the cyclone at the very top of the troposphere. Last night (Tuesday night) I observed a beautiful side-effect of this. The full moon was surrounded by a lunar corona, a band of rainbow colours. As the high-level cloud drifted past, the ring distorted gently as different sections shifted in and out. It was so beautiful!

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