Floods and record rain in WA Kimberley and NT Top End
Thu 1 Feb 2018

A particularly active phase of the Australian Monsoon in late January has flooded and isolated an area of the WA Kimberley twice the size of Victoria and brought flooding, evacuations and damage across the NT Top End.

In the last week of January, the Australian Monsoon trough lay from the WA Kimberley though the NT Top End to Cape York. From late Friday 26 January, tropical depressions began to form in the East and West Kimberley, and by late on Sunday 28th had coalesced into a deepening depression near Broome WA. This depression remained near Broome with a central pressure dropping as low as 985hPa until late Tuesday 30th, when it moved away to the SW and weakened.

Rainfall for the week to 9am Wednesday 31 January. There were falls over 700mm in both the WA Kimberley and the NW Top End of the NT, with some amounts over 600mm on Cape York Peninsula, QLD, thanks to the presence of the active monsoon trough. BoM

In Western Australia, Broome and its immediate vicinity had the worst of the weather, with 412.2mm falling steadily over the 24 hours to 9am on the Tuesday 30th as the nearby low pulled abundant moisture in from the Indian Ocean. As a daily total, this came second only to the 476.6mm on 30 January 1997 in a rainfall record going back to 1889. However, the WA BoM noted on Facebook that "Broome has recorded 697.2mm in the past 5 days which is the highest 5-day total on record going back to 1889. The previous highest 5-day total was 667.4mm in 1978. Broome also received their highest monthly rainfall on record with 942.2mm!"

This extraordinary ABC video taken from a high-range 4WD on the Great Northern Highway south of Broome gives a good feel for conditions after the torrential rain of 29/30 January. This YouTube compilation* by Posty Broome gives an idea of conditions in Broome. Despite the rain, barometer readings down to 985hPa and wind gusting to 102km/h at Broome Airport late Monday evening, the Bureau did not issue a Cyclone Warning because, although it had all the appearance of a Category 1 Tropical Cyclone, it actually wasn't one. It was a tropical low, over land in the monsoon trough, and didn't have the sustained winds of at least 120km/h required to reach cyclone status. The BoM's Steph Bond explained the distinction in this ABC article, which also detailed the damage wrought in Broome, and pointed out politely that perhaps people should listen to the Bureau's Severe Weather Warnings more closely.

The rain in WA's north follows hard on the heels of heavy falls from Tropical Cyclone Joyce around 11 January and TC Hilda just after Christmas. These three events, with other good falls from monsoonal showers and thunderstorms, are making life difficult for pastoralists at present. But they follow on from a poor wet season so far, and set up the country for continued good conditions, as described by ABC Rural WA.

Meanwhile, in the Northern Territory, the heaviest rainfall and worst flooding was in the NW of the Top End and particularly in the Daly River catchment. By early Wednesday 31 January, the river in Daly River township had reached 3.5m above major flood level after 252mm was recorded there in the 24 hours to 09.00 Tuesday 30th. Some 380 residents, more than half the population, either self-evacuated or were evacuated by helicopter and bus.

Coming after a half-hearted start to the wet season, the heavy rain was welcomed by pastoralists [ABC Rural NT], with a number of cattle stations getting record January falls, including Wave Hill with 445mm, Tanumbirini 597mm and Labelle Downs 1,138.0mm (January average 390.9). The Darwin area also had heavy January totals, helped by fierce storms on Monday 29 January. Some of the highest were Darwin River Dam 955.8 (average 364.8), Edith Valley, 30km SE of Darwin, 991.2 (388.1), nearby Humpty Doo 1204.8 (446.6), and other locations near Darwin and Batchelor that exceeded 900mm.

As often happens, there were a number of very readable stories to come out of the event:

• A trio of Danish tourists became stranded when their car hit a rock while attempting to cross the Robinson River in the Gulf of Carpentaria. Their escape, as water began entering their car and they spotted a croc lurking is one they'll dine out on for decades.
• It's not only the humans having problems. This story of orphaned joey Steve, picked up "sitting there exhausted and shivering" by a motorist is typical of the stresses on wildlife caused by monsoonal rain and flooding.
• Widespead telephone outages in the NW Top End caused problems, while emergency services became more and more angry at the number of unnecessary rescues they were called on to make. "We would ask people not to be idiots and stay out of floodways"
• Surf's up! The BoM NT Facebook page showed that high tides and heavy surf brought the surfboards out. As well as a few crocs catching the waves.
• BoM spokesman Greg Browning said that "the monsoon onset was actually one of the latest we've had on record; it's actually the fourth-latest since 1957, which is when records really started". Rainfall records were broken as far afield as the Darwin area and Uluru. New records are given in the records section of each day's AWN Daily Weather Summary.

Most Australians never experience the intrigue, drama and majesty that is the Australian Monsoon. This is it, encapsulated in one stunning photo by Jacci Ingham.

[Thanks also to Floodlist, Oz Cyclone Chasers.]