Wet Behind The Years

Wet-season rain in tropical North Queensland is largely due to a macroclimatic (very large area) convergence of weather systems that form what is commonly known as the monsoonal trough.

The monsoonal trough is a band of unstable atmospheric activity that forms at the point where the south-east trade winds (pushing north-west) meet the equatorial westerlies (which blow south-east).

Put simply, it is the collision of these two warm, moist, rising air streams that create the heavy wet season rain that is associated with thunderstorms and tropical cyclones to the north-east.

The monsoon trough appears seasonally on satellite imagery during October to March as a single line of cloud, although at times, it may seem to be a little more scattered or random.

Okay class, now this is where weather gets sexy. What about our own little microclimatic (localised) system, what effect does our local weather system have on our lifestyles (non-condomic) and what influences it?

Our micro-climate has several local influences including the Great Barrier Reef to the east and the elevated Tablelands to the west. As the sea-breeze blows across the warm shallow reef, the sea surrenders moisture, this moisture is then taken as humidity by the breeze and pushed up into the mountains.

The warm moisture laden air tries to rise like a hot air balloon but gets trapped in the mountains by the cool dry air from the Tablelands.

A good analogy of cool air pressure is when you open the fridge on a hot day, you will feel the cold air drop at your feet and not lift up to your face. Cool air is heavy, so, grab us both a tinnie out and close the door before the flies get in!

The cool dry air sits weightily atop of the warm moist air that continues to rise, as it rises, it will eventually come into contact with the cool dry tablelands air. This process cools the once warm air, contracting the moisture particles together which in turn forms rain drops.

In short, humidity is trapped up in the mountains, the hot moist air rises up to meet the cool air of the Tablelands and then drops back down through the warm air and so on it goes.

It will often rain in the mountains as the moisture laden air reaches a critical mass, but generally speaking the humidity will stay trapped in the mountains cycling through warm, cool, warm, lifting and falling until the evening.

Still here? Hey, I am really proud of you for following me thus far, the best bits are still yet to come I promise. In the evenings, we experience a natural phenomena the local farmers refer to as the ‘land breeze’. Its meteorologically correct name is an atmospheric inversion.

To explain, as the sun rises, it warms up the atmosphere to the east and the elevated Tablelands to the west remain cool. As the day progresses and the sun goes over the mountains to the west toward Dimbulah, the atmosphere to the east starts to cool down and the tablelands dry air starts to warm.

These two systems eventually reach an equilibrium, sometime between 7 o’clock and 9 o’clock in the evenings. This is when you will start to feel a gentle breeze coming from the west, as it drops down over the mountains to meet the cooling coastal night air.

It was this land breeze that was very important to the cane farmers in days gone by. It was during this gentle westerly that it was (and still is) the safest time for the farmers to control or ‘draw’ burn the sugar cane fields without setting the entire crop alight!

This inversion or land breeze from the west pulls all of that built up moisture laden rain cloud out of the mountains, raining all the way out to sea and at sunrise the next day, the whole process starts all over again. Have you ever noticed how the rain, falls mainly on the plains, at night?

I find the best way to explain our local weather to the visitors, is to tell them that the Complex Mesophyll Vine forests of the Greater Daintree region are here because of the unique rainforest animals.

These unique little ‘locals’ are here to enjoy an over-abundance of fresh water and this over-abundance of fresh water is a direct result of the natural interactions between the Great Barrier Reef, the Mountain Rainforests and the Tablelands. Howzat for Harmony!

I’m such a romantic!