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A slow-moving high pressure system established itself in the Tasman Sea, directing a warmer north-west to north-east flow across much of southern Australia. This high pressure system is often referred to as a 'blocking high'.

The high pressure system remains nearly stationary for several days, with warm northerly winds continuing to flow across the affected regions.

Higher-than-average temperatures are experienced, with the daily maxima ranging fromt he mid-30s to low-40s everyday. Night-time temperatures also tend to be higher than average. Winds tend to be light to moderate.

A change to cooler conditions is generally associated with the passage of a cold front. Winds become fresh to strong and gusty as the front moves over the area. Temperatures tend to decrease rapidly once the front has passed. 

• Area affected: Most of southern Australia, particularly the south-east 
• When: Blocking highs can occur at any time of  year, however temperatures only tend to reach the mid-30s and higher during the mid-late summer and early autumn period.
• Duration: Hot spells can last from a few days to a few weeks (extreme end of the scale).

During the northern wet season (October to April) the temperatures increase and humidity rises. The monsoon trough moves into the Southern Hemisphere and its movement dictates the nature of the monsoon at any time.

During 'active' periods of the monsoon (the monsoon trough is over landacross northern Australia), there are sustained periods of rainfall, increasing the humidity, but decreasing the temperature.

In contrast, when the monsoon trough is in the Southern Hemisphere, but to the north of the continent, humidity increaes and temperatures remain high. This is termed a 'break' period of the monsoon. Localised storms characterise the monsoon's break periods.

During break periods, and before the onset of the monsoon, a moist east to noerth-east flow is directed onto the norht Queensland coast. This onshore flow interacts with the region's topography and there are often isolated storms during the afternoon.

At this time of year, the temperature usually reaches the low to mid-30s, and the humidity is moderately high. When a storm passes overhead, the rainfall increae the moisture available in the region.

The temperature drops slightly while it is raining, however the storms are short in duration, and the temperature is quick to increae again once the storm has passed.

After the storm has moved away, temperatures return to close to their former level, in the low to mid-30s. Hoever, the extra moisture available dramatically increases the region's humidity, causing an increase in the THI.

Wind before the storm tend to be moderate to fresh, becoming strong and gusty during the storm, before returning to a moderate to fresh flow.

• Area affected: Most of tropical northern Australia
• When: Wet season storms generally occur between October and April.
• Duration: Storm events are short-lived, lasting a couple of hours at the most, however it may take several hours after a storm's passing for the increased humidity to moderate.

This is similar to Scenario 1 - a slow-moving high pressure system establishes itself in the Tasman Sea, directing a warm north-west to north-east flow across uch of southern Australia.

When this situation occurs during spring or early summer, it can lead to an early warm spell across southern Australia.

Maximum temperatures can reach the high 20s to low 30s, while the minimum temperatures remain in the low teens.

The winds tend to be light to moderate, increasing to fresh to strong and gusty as the cold front approaches.

• Area affected: Most of southern Australia, particularly the south-east
• When: Blocking highs can occur at any time of year, however early warm spells occur during spring and early summer.
• Duration: Warm spells can last from between a few days to a few weeks (extreme end of the scale).

The west coast trough is a semi-permanent feature of the surface pressure pattern near the west coast of Australia during the warmer months, and is the dominant influence on west coast weather conditions at this time.

The trough is a zone of low pressure that develops at the boundary between warm continental easterly winds and cooler maritime air from the Indian Ocean.

Initially, the trough tends to lie near the west caost of Australia and will remain there over a period of several days.

Areas to the east of the trough are under the influence of warm north-easterly winds. These areas can experience hot days with maximum temperatures in excess of 40 degrees, and the possibility of thunderstorms. Winds near the trough tend to be light to moderate.

Eventually an approaching cold front will push the trough inland, bringing with it a welsome cool change. 

• Area affected: South-western Australia
• When: West coast troughs occur during the warmer months, from mid-spring through to mid-autumn.
• Duration: Each development cycle of the west coast trough lasts for a few days to a week.