Unseasonable heavy rain drenching northeast NSW, eastern Queensland

Unseasonably heavy rain is drenching northeast NSW and parts of eastern QLD, bringing the heaviest August rain in decades to some locations, with potential record falls over the next 24-48 hours. 

An upper trough over inland NSW and QLD is helping amplify a broad low pressure trough extending down the QLD coast and into northeast NSW and small low pressure system off the central QLD Coast. This system is being fed by a deep onshore flow off the Coral Sea, pumping the system full of moisture. This type of system is quite atypical for August, and more typical of summer and autumn.

Yesterday, widespread heavy falls of 50-100mm drenched QLD's Herbert and Lower Burdekin district, with some areas seeing their heaviest August totals in more than two decades, including Townsville which had its best August rain since 1998, recording 67mm to 9am today. There were also reports of small hail in some parts of Townsville, which is exceptionally rare at any time of the year.

Further south, northeast NSW has also been copping a drenching, with widespread falls of 50-150mm recorded in the 24 hours to 9am today. Whilst these sorts of rain totals aren't as unusual in this part of the world as this time of year, Ballina's 116mm to 9am today was still the wettest August day since 2014. Heavy rain has continued to fall in this area today, with parts of the Byron Bay Hinterland seeing accumulated event totals in excess of 250mm as of 3pm EST today, with rain continuing to fall.

Over the next 24-48 hours the focus will be on the small low pressure system off the central QLD coast, which is expected to move south and bring heavy rain to the south of the low (with rapid clearing on the northside of the low). Depending on the movement and intensity of this low, which models are struggling to predict, record August falls are possible across parts of the southern Capricornia, Wide Bay and far northern Southeast Coast districts. From later today and into Wednesday morning, widespread falls of 100-200mm are expected across these areas, with some models indicating isolated totals of up to 300mm possible. Seventeen Seventy's highest monthly August total on record is 147.4mm, Gladstone 141.6mm and Bundaberg 134.8mm, so if these sorts of falls do occur records will be broken.

A secondary burst of heavy rain will move into southeast QLD and northeast NSW on Wednesday as well, clearing off by early Thursday morning. Widespread falls of 50-100mm are likely over the region, with some areas (particularly the NSW/QLD Border Ranges and northeast NSW) seeing localised falls up to 200mm. Minor riverine flooding and flash flooding is expected, with moderate flooding possible over parts of northeast NSW. 

The system will finally clear off by Thursday, with several warm days likely in the wake of the system before a cooler change over the weekend.