There isn’t much that can keep you and your kayak off the water. In 2008, I managed to paddle for 41 days straight, unimpeded by the weather. However, there are days when you’re better off keeping your Ugg Boots on and switching on the TV to see what Bear Grylls is up to in his latest adventure.
It is important to always check the forecast and the likely impact of the weather on your plans. Strong winds, thunderstorms, and hail are not our friends and are best avoided.
In a kit that has been created for schools, the Australian Bureau of Meteorology explains that “Weather is a description of what’s happening with the air, sun, rain, and wind when you go outside.” This means that you can check the weather simply by getting off the couch and going out of the house.
Making predictions is a little trickier, although meteorologists have identified consistent patterns that can help. These patterns are the basis of forecasts reported in daily newspapers, TV broadcasts, and on the internet. The Bureau of Meteorology, WillyWeather, and Weatherzone websites and mobile apps are all excellent sources of information.
Weather patterns are driven by the interaction of the sun, air, and water. They are also influenced by the rotation of the earth, both on its own axis and around the sun.
When the sun heats the surface of the earth in a particular place, the air above it rises. This reduces the air pressure at sea level and creates what is known as a low pressure system. When the air falls back down again, the pressure increases and creates a high pressure system. In an attempt to restore balance, Mother Nature moves air from areas of high pressure to areas of low pressure until both are equal. This movement of air is what we call wind. The greater the difference in sea level pressure, the stronger the wind. For the purpose of illustrating these differences meteorologists produce synoptic charts like this one from the Bureau of Meteorology. Lines called isobars connect points of equal pressure and are superimposed over a map of the relevant area, and high and low pressure systems are indicated by ‘H’ and ‘L’ respectively.
The wind doesn’t blow directly from a high pressure system to a low pressure system. Due to a phenomenon known as the Coriolis effect, the flow of air in the Southern Hemisphere is deflected to the left. This means it moves anti-clockwise around high pressure systems and clockwise around low pressure systems. Interestingly, the opposite occurs in the Northern Hemisphere. If you know the position of the prevailing system, you can also predict the wind direction.
For longer range forecasts, it is useful to remember that pressure systems are not static. They move across Australia from west to east. It is therefore possible to forecast the weather by tracking their progress.
A complication in coastal areas is the “sea breeze” that springs up on summer days when the land becomes much hotter than the sea. When hot air above the land rises, cooler air from over the sea moves in to take its place. In eastern Australia, you would naturally expect this to come directly from the east, but the Coriolis effect is at work again, deflecting the flow to the left. That’s why our sea breezes come from the northeast. In the evening, the land cools and the wind subsides. In some cases, the land becomes cooler than the sea during the night and a gentle offshore breeze picks up. This is usually weaker than a sea breeze because the temperature difference is smaller.
Unsettled conditions and rain are usually associated with low pressure systems. The rising air carries water vapour, primarily in the form of evaporation from oceans, rivers, and lakes. As it rises, it cools, and the water condenses into droplets which form clouds and later rain, hail, and snow. If conditions are particularly hot and humid, fast-rising air can create a thunderstorm. Calm and sunny conditions are generally associated with high pressure systems. This is because the dry air is settling slowly back down to earth.