In Queensland, Ridgy patrols the pressure pattern over southern areas. In winter in the south, he lets through cold, wet fronts, and in the north lets trade winds and their showers get going. In summer in the north, Ridgy helps bring on the monsoon, and leaves the south fine and dry.

Enso herds moisture from the Pacific Ocean towards Queensland. When there’s an El Nino, he causes less rainfall and fewer tropical cyclones. During La Ninas, he chases greater amounts of moist tropical air across Australia and causes more tropical cyclones.

Mojo loves to mess around in tropical areas – he can influence when the monsoon starts, and is most active from October to April.

Eastie scampers along the south-east coast of Australia, can go into action overnight, and his favourite seasons are autumn and winter. He can cause strong winds, heavy rains and lots of rough weather.

Indy can sometimes herd moisture across from the Indian Ocean to parts of the state in winter-spring, depending on whether he’s feeling positive or negative.

Sam can come to play in Queensland – sometimes bringing some cold wintery weather from the south affecting rainfall in winter, and sometimes gets working in spring and summer to bring more rainfall to south-eastern parts of the state.

The roundupEnsoIndyRidgySamEastieMojo
animated dogs rounding up weather on a map of Australia animated dog called Enso animated dog called Indy animated dog called Ridgy animated dog called Sam animated dog called Eastie animated dog called Mojo



Figure 1. The major weather and climate drivers across Australia (Bureau of Meteorology, 2010)



Queensland's main climatic drivers are summarised in Table 1.

Table 1. Summary of Queensland’s main climatic drivers of weather

Climatic driver Potential effect When it is active Where in Queensland it has most effect
Sub-tropical ridge

position is favourable for frontal activity

fine and dry

position is favourable for monsoon onset

trade winds





southern parts

southern parts

northern parts

northern parts

El Niño – Southern Oscillation

El Niño - less rain, fewer tropical cyclones

La Niña - more rain, more tropical cyclones

usually running from May - April; greatest effect (most often) in winter/spring statewide
The monsoon rainfall, often heavy October - April tropical areas
Madden-Julian Oscillation influences the timing of the onset of the monsoon; connected to tropical cycles October - April tropical areas
Trade winds showers April - September tropical and subtropical areas to the east of the Great Dividing Range
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These climatic drivers are can modify synoptic features as summarised in Table 2.

Table 2. Summary of Queensland’s synoptic features

Synoptic feature Potential effect When it is most active Where in Queensland it has most effect
Tropical cyclones and tropical depressions heavy rainfall, strong winds, damaging storm surges (worse for cyclones than depressions)

October - April

(cyclone season is November - April)

tropical areas and sub-tropical parts
Cut-off lows and east-coast lows rainfall with strong gusty winds March - October southern Queensland
The inland trough

showers and thunderstorms

heavier rainfall and strong winds when interacting with other systems

September - May most of Queensland
Cloud bands rainfall April - September statewide
Frontal systems

westerly change – drizzle

south-easterly change

– afternoon thunderstorms


winter and spring

summer and autumn

southern Queensland

south-east Queensland

Blocking highs coastal showers if high is located in the Tasman all year south-east Queensland
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Sub-tropical ridge

The sub-tropical ridge, an extensive area of high pressure, is a major feature of the general circulation of our atmosphere. It is a major influence on the climate of Australia.

Its position varies with the seasons, moving north in winter which results in drier conditions over Queensland.

North of the sub-tropical ridge, towards the equator, is the trade wind belt of predominantly south-easterly winds which blow towards the monsoon trough.

The movement of this trough is relatively small over ocean areas but as summer approaches and the land heats up it moves as far south as northern Australia.

This triggers the onset of the monsoon as warm moist air moves in from the northwest, replacing the drier air of the trade winds.

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El Niño - Southern Oscillation

Areas in Australia affected by El Nino

Figure 2. ENSO - areas affected, timing and duration

Sea surface temperatures in the Pacific Ocean can affect rainfall across the eastern half of Australia, including Queensland.

The El Niño - Southern Oscillation (ENSO) is a major influence on eastern Australia’s climate including almost all of Queensland.

ENSO is the irregular oscillation between El Niño and La Niña conditions, which describe the variations in atmospheric patterns across the Pacific Ocean, and variations in sea surface temperatures in the central and eastern tropical Pacific Ocean.

El Niño

El Niño is associated with extensive warming of the sea surface in the central and eastern tropical Pacific.

It is often associated with below average winter/spring rainfall over much of eastern Australia.

Tropical cyclones are generally less frequent during El Niño events.

The El Niño event of 2002–03 seriously affected rainfall over Queensland (Figure 3). Rainfall was well below average across the state, with many areas experiencing severe water shortages.

Figure 3. Sea surface temperatures in November 2002 (left) and the below average rainfall in Queensland associated with the 2002–03 El Niño event (right)

La Niña

La Niña is associated with extensive cooling of the sea surface in the central and eastern tropical Pacific.

It is often associated with above average winter/spring/summer rainfall over much of eastern Australia.

Tropical cyclones are often more frequent during La Niña events.


El Niño Modoki

‘Modoki’ is Japanese for ‘similar, but different’ - as such, El Niño Modoki is a phenomenon under scrutiny. It is not yet clear whether El Niño Modoki is a different climate driver to conventional El Niño.

El Niño Modoki is associated with strong warming of sea surface temperatures in the central tropical Pacific and cooler sea surface temperatures in eastern and western tropical Pacific waters.

(Conventional El Niño conditions are usually associated with warm sea surface temperatures in the eastern tropical Pacific.)

In northern Australia, El Niño Modoki events are associated with:

  • a delayed, but shorter and more intense monsoon season
  • increased rainfall in January and February
  • decreased rainfall in December and March.

They also appear to cause a large-scale decrease in autumn rainfall over north-western and northern Australia.

The El Niño Modoki phenomenon is thought to have become more frequent than conventional El Niños since the late 1970s, occurring in 2002, 2004 and 2009.

Researchers need to observe more years of climate data to understand if El Niño Modoki is different and, if so, how it may affect Australian rainfall differently to ENSO.

Tropical cyclones are often less frequent during El Niño events.

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The monsoon

The term ‘monsoon’ is used to describe the seasonal reversal of winds that occurs over parts of the tropics.

As the Australian summer approaches, the continent heats up. Low pressure is created, which effectively draws the monsoon trough—a zone of low pressure and rising air—over northern Australia.

This trough draws in moist air from the surrounding oceans and we refer to this influx of moist air as the monsoon.

The monsoon in northern Australia usually occurs between December and March. The wet season encompasses the monsoon months but extends several months either side (October to April). Generally, April is a transitional month and by May trade winds are well established again over Queensland.

The monsoon can be in either an ‘active’ or an ‘inactive’ phase.

Active phase monsoon

The active phase is usually associated with broad areas of cloud and rain, with sustained moderate to fresh north-westerly winds on the north side of the trough.

Widespread heavy rainfall can occur during active phases.

Inactive phase monsoon

An inactive phase or ’break’ period occurs when the monsoon trough temporarily weakens or retreats north of Australia.

It is characterised by light winds and isolated shower and thunderstorm activity, sometimes with gusty squall lines. A squall line is a long line of thunderstorm cells, sometimes several hundred kilometres in extent.

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The Madden-Julian Oscillation

Map showing areas affected by MJO and when


The Madden-Julian Oscillation (MJO) is a large-scale slow-moving band of increased cloudiness that travels eastwards in the tropics.

It moves around the globe along the equator, ‘pulsing’ roughly every 30–60 days.

The signal of the MJO in the tropical atmosphere is not always present, making it hard to detect at times.

The MJO influences the timing of the onset of the monsoon and can also influence the transitions from active to inactive monsoon phases.

Tropical cyclones are more likely to develop when the MJO is active in Australian regions.

MOJO the Climatedog is one of 5 animated sheepdogs (The Climatedogs) developed by the New South Wales Department of Primary Industries (in collaboration with the Victoria Department of Primary Industries and the Bureau of Meteorology) to help farmers understand the climate processes that affect rainfall variability.

At just under 2 minutes long, MOJO is a quick, clear and fun way to learn about the Madden-Julian Oscillation.

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Trade winds

Figure 5. Trade winds - areas affected, timing and duration


Trade winds blow from an east-to-southeast direction across much of the southern hemisphere tropics.

They prevail along the east coast of Queensland.

They collect moisture as they move eastward over the tropical Pacific Ocean towards the east coast of Australia and bring rainfall to tropical and sub-tropical areas of the east coast.

The impact of the trade winds is greatest from April to September (the darker blue on the scale in Figure 5). Winds of 45 to 55 km/h are often observed north of around Cooktown at this time.

Trade winds are at their strongest when a slow-moving high pressure system is located off the east coast of Australia in the Tasman Sea. This is when we get strong wind warnings.

The most significant rainfall driven by the trade winds occurs on the eastern side of the Great Dividing Range, with some places there, such as Bellenden Ker, being among Australia’s wettest places.

Figure 6. Average annual rainfall in Queensland 1961–90, showing the influence of the prevailing southeast winds

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Tropical cyclones

Figure 7. Tropical cyclones - areas affected, timing and duration


Tropical cyclones are very intense low-pressure systems that produce heavy rainfall, destructive winds and damaging storm surges.

They have wind gusts in excess of 90 km/h around their centres; in the most severe cyclones, gusts can exceed 280 km/h.

These winds can cause extensive property damage and turn airborne debris into potentially lethal missiles.

The cyclone season starts in November and finishes at the end of April, but occasionally tropical cyclones have been known to form during May.

On 10 March 2005, severe Tropical Cyclone Ingrid crossed the east coast of Queensland, south of Lockhart River (Figure 8). Small in size, but very intense, Ingrid is the only severe tropical cyclone in recorded history to impact the coastlines of three states/territories.

At the coastal crossing point, many trees were defoliated, stripped of bark, and felled. A 2.7-metre storm tide inundated the coast 60 kilometres south of the Lockhart River township.

Rainfall exceeded 200 mm in parts of far north Queensland—small amounts for a cyclone, partly due to Ingrid’s small size.


Figure 8. Tropical cyclone Ingrid, 2005 - track map (left) and satellite image (right)

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Tropical depressions

Tropical depressions are moderate-strength low-pressure systems, often associated with the monsoon trough.

They may develop into tropical cyclones if conditions are favourable.

They often produce significant rainfall and strong and gusty winds.

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Cut-off lows and east-coast lows

Figure 9. Cut-off lows - areas affected, timing and duration


Cut-off lows are low-pressure systems that break away from the main belt of low pressure that lies across the Southern Ocean.

They are associated with sustained rainfall and can produce strong, gusty winds and high seas.

If a cut-off low is slow-moving or near-stationary, rainfall may occur for extended periods and may be heavy at times.

East-coast lows are a type of cut-off low which occur off the eastern coast of Australia, on average several times a year.


Figure 10. Queensland rainfall (upper panel) associated with a cut-off low (lower panel), August 2007. The cut-off low brought strong to gale-force winds and dangerous surf to exposed parts of south-east Queensland from 21 to 24 August 2007. Torrential rainfall occurred over parts of the Southeast Coast and Wide Bay districts, with some very high daily totals resulting in flash flooding at Tewantin and Noosaville on the 23rd and 24th. This was a very rare rainfall event for Queensland in August.


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The inland trough

Figure 11. Inland trough - areas affected, timing and duration


The inland trough (also known as the easterly trough), or dry line, is a semi-permanent feature of the synoptic pattern over the interior of Queensland.

It is most developed and active during the warmer months.

The trough is located on the lee side (inland side) of the Great Dividing Range, forming a boundary between the moist air near the coast and dry air inland. It extends through central Queensland and into central New South Wales.

It is partly formed by the intense heating of the land during warmer months, but the topography of the region also plays a role.

As the temperature rises during the day, the trough deepens and moves towards the coast, often causing showers and thunderstorms to form in the moist unstable air to its east.

Rainfall can be particularly heavy when the trough interacts with other features, such as a cold front or a mid- or upper-level trough in the atmosphere.


Figure 12. Queensland rainfall (upper panel) associated with the inland trough (lower panel), 9 October 2007. Showers and thunderstorms developed in the unstable air east of the inland trough. An upper-level trough increased the activity about the southeast of the state and several ‘supercell’ thunderstorms (intense thunderstorms which can last for many hours) developed, producing brief but heavy rainfall, strong winds and large hail.


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Cloud bands

Figure 13. Cloud bands - areas affected, timing and duration


A cloud band is an extensive layer of cloud that can stretch across Australia, often from north-west to south-east.

Cloud bands can form when a trough of low pressure occurs in the upper levels of the atmosphere, or when warm, moist tropical air originating over the Indian Ocean moves towards the pole (generally south-eastward), and is forced to rise over colder air in southern Australia.

Cloud bands originating over the Indian Ocean generally slide south-east as they approach Queensland and are often poor rain producers over the state.

Cloud bands associated with upper troughs that are most developed over central and eastern parts of the Australian continent generally produce much more rain over Queensland.

Upper troughs and upper low-pressure systems are often key contributors to widespread rain over central and southern Queensland in autumn and early winter.

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Frontal systems (or changes)

Figure 14. Frontal changes - areas affected, timing and duration


Frontal changes, such as cold fronts, generally move from west to east across the Southern Ocean and vary in their intensity and speed.

Cold fronts affecting Queensland, which are often referred to as troughs or wind changes, are broadly of two types:

  • westerly (or south-westerly) changes, which are most common during winter and spring
  • south-east changes, which are most common during summer and autumn

Westerly change

Westerly changes keep some of the structure of a cold front, but are altered by their long journey across the Australian continent. They are most developed over southern Queensland, but sometimes extend well into the tropics.

They are generally followed by little cloud; however, if there is a deep low-pressure system in the Tasman Sea directing cold moist air over southern Queensland, drizzle may occur about the western slopes of the Great Dividing Range.

South-east change

The arrival time of a south-east change in south-east Queensland is often critical to the development of thunderstorms, with greater heat and instability making the latter part of the afternoon most favourable for thunderstorm development. The over-land section of a south-east change will often merge with the inland trough.

The near-coastal section is modified and turned north by the prominent coast of south-east Australia and by the Great Dividing Range, reaching the Queensland coast as a northward-moving south-east (sometimes southerly) change.

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Blocking highs

Figure 15. Blocking highs - areas affected, timing and duration


Blocking highs are strong high-pressure systems that form further south than the usual position of the sub-tropical ridge, and remain near-stationary for an extended period of time.

They block the west-to-east progression of weather systems across southern Australia, and are usually formed in the Great Australian Bight or the Tasman Sea.

A blocking high’s impact on the weather varies depending on its location and the systems around it.

A blocking high can produce wet and showery conditions in south-east Queensland, as a sustained onshore flow brings showers to areas near the coast.

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Australian climate influences - The Bureau of Meteorology

Antarctic Oscillation Index (Southern Annular Mode) – US National Weather Service

Coughlan, M 1983, ‘A comparative climatology of blocking action in the two hemispheres’, Aust. Met. Mag., vol. 31, pp. 3–13.

Hendon, H, Thompson, D & Wheeler, M 2007 ’Australian rainfall and surface temperature variations associated with the southern annular mode’, J. Climate, vol. 20, pp. 2452–67.

McBride, J & Nicholls, N 1983, ‘Seasonal relationships between Australian rainfall and the Southern Oscillation’. Monthly Weather Review, vol. 111, pp. 1998–2004.

Saji NH, Goswami BN, Vinayachandran PN & Yamagata T 1999, ‘A dipole mode in the tropical Indian Ocean’, Nature , vol. 401, pp. 360–63.

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