Anyone in Brisbane without air conditioning would have found it hard to sleep last night, as cloud cover and high humidity kept the overnight minimum to a stifling 24.7ºC.

The minimum occurred at 4:30am, feeling more like 28.3ºC. The dewpoint temperature at the time was 21.2ºC with relative humidity at 81%. Things tend to get uncomfortable from about 60% relative humidity, so ceiling fans would have been next to useless.

 Image: temperaturatures in Brisbane and surrounding areas at 4:30am EST on Saturday.

Responsible for the sultry conditions is a broad trough over southeast Queensland, which extends from the northwest tropics. The trough is dragging tropical moisture towards Brisbane, making it feel like the capital city is about 10 degrees of latitude closer to the equator. Saturday's minimum was over four degrees above the average for this time of year, and it's set to continue well into next week.

The trough maintaining high humidity will remain over Brisbane and southeast Queensland until Wednesday, when a high pressure ridge moving up the coast forces the trough northward. Until then, expect nights to only dip to 23-25 degrees. Making matters worse, a tropical low forming over the northwest tropics should send a stream of increased moisture towards Brisbane in the coming days, increasing humidity further.

Accompanying the ridge on Wednesday will be a south-southeast wind change, bringing relief from the humid northerlies that will persist until then.