Wet season signals

A burst of rain is on its way to North Queensland this weekend. It will start with showers along the Far North Queensland (FNQ) coast, then briefly spread into the nearby mountains before easing back out over the Coral Sea. This happens because of a “trough” – basically a long zone of lower air pressure – which is shown as pink dashes on weather maps.

As this trough deepens, it pulls most of the rain away from the land and out to sea. That’s a fairly early hint of the kind of patterns we often see in the wet season.

What’s more interesting right now is the amount of rain happening along the equator, which has recently affected Bali. In the wet season, a system like that could move towards the FNQ coast and bring a lot of rain. If the “monsoon trough” (a broad band of unsettled, rainy weather that often sits across northern Australia) were to shift south at the same time, that rain could reach further down past Ingham. These are just signs of how the atmosphere is setting up – it doesn’t mean we can lock in exact events this far out.

Another key influence will be the movement of high-pressure systems further south. My early checks suggest the highs look to be coming through in a regular pattern.

From looking at the last five years of rainfall in Townsville, I’ve noticed that the heaviest rain tends to happen when air pressure is particularly low over Darwin. This is linked to something called the Southern Oscillation Index (SOI), which measures pressure differences between Darwin and Tahiti. When the SOI is high, it usually means better chances of rain in Queensland. This cycle seems to have been trending upwards over the past five years.

So for this weekend, I don’t expect massive totals – most places will only get light falls, though a few spots could collect 50 mm or a bit more.