The Monsoonal Climate of the Top End
The weather in the Top End can be described as always warm, it is rarely above 35°C and there are only a few occasions when the night-time temperature drops below 15°C. Warm may be an understatement for all is relative, the weather may be described as hot depending on where you come from, and when you come. One things for certain, be sun-smart and drink plenty of water.
Although the local Aboriginal populations describe up to six seasons we, north of the Tropic of Capricorn mainly refer to only two. The Wet Season and the Dry Season.
The Dry Season
The Dry season occurs generally between April and October, perfect blue skies are a feature of this season which starts off green, then the waters slowly retreat to just those few permanent watercourses. This means that the waterfalls will slow or even stop, and the floor of the landscape becomes a tanned light brown. The limited water means better access for visitors as dry season only roads are reopened, and there is a concentration of animal life around the billabongs. The warm days are complimented by cool starry nights.
The Wet Season
The Wet Season generally occurs between November and March, featuring this season is the slow building of storms, and the magnificent light shows and thunder that they bring. By January the the floodplains are swollen, the afternoon storms are consistent and the overcast sky brings some protection from the hot sun. The overflow of water forces the animals to retreat to higher ground, and the full strength of some waterfalls is motivation for closure to swimming. Small flowers bloom, and the green sorghum grass grows high throughout the bush land as cool rains bring temporary relief from the humidity and heat.
The Shoulder Seasons
The shoulder seasons, are the periods that occur with the changing of the seasons, they are often described as the Build-Up, for when Dry Season becomes Wet Season, and the Run-off, when the Wet Season becomes the Dry.
Although often regarded as the most uncomfortable time to visit the Top End, it is the best time to see the thunder storms. The humidity builds-up quickly, and the bright sunny days make the heat stronger so the swimming holes are so much more rewarding.
During the Run-Off the storms become less frequent and the weather will start to cool. This season's title is a reference to the water running off the floodplains and back into the creeks and rivers. It is also a reference to fishing conditions as a good time to catch the elusive Barramundie as the fish and nutrients flow back into the rivers with the water.
Surprisingly the temperature doesn't change much from day to night, or from season to season. The average variation from day to night is 8.5°C, and the average variation from the coldest season to the hottest season 2.8°C. The highest recorded temperature in Darwin is 38.9°C and 10.4°C is the lowest.
Obviously most of the rainfall occurs during the Wet Season. In the Dry Season some uncharacteristic light rains do occur but most months in the dry Season are without any cloud. Darwin's highest recorded annual rainfall occurred in 1998 when 2906ml were collected. In the Northern Territory the highest rainfall in one day, collected on the 15th of April 1963 from Roper River was 544.6ml.
The Relative Humidity
The Wet Season brings with it the humidity.
What is Relative Humidity?
Relative Humidity is a traditional way of measuring the moisture content of air. It is measured as a percentage of water vapour in the air when compared to when the air is saturated and can hold no more moisture, i.e.; 100%. It is important to realise that this humidity is relative to temperature as different temperatures have different levels of moisture at saturation level. A temperature of 35°C can hold lots more moisture than at 25°C.
Humans are sensitive to humid air because we use mainly evaporative cooling to regulate temperature. In humid conditions the rate of perspiration from the skin is lower than that in dryer conditions. The body then would act in humid conditions the same as it would act in hot conditions. Humans perceive this rate of heat transfer as body temperature rather than the body temperature itself, we therefore feel warmer when the relative humidity is high.
This is due to the fact that during humid conditions the human body has to work harder to cool itself, like its harder to dry washing on a humid day. If the temperature is 30°C and the relative humidity is 0%, then it would feel like its 26°C. If the temperature is 30°C and the relative humidity is 100% then it would feel like its 34°C. Something to remember in November.
For information on how to prepare and what to bring on your tour in the Top End click here.
(Chart statistics sourced from the BOM website.)