Townsville, trapped in a weather ‘convergence’ zone, braces for more flooding

Author : mamun Published: February 04, 2019

Updated

February 05, 2019 08:48:41

A monsoon trough and a low pressure system are causing mass flooding in Queensland.

A very active monsoon trough that is refusing to budge and a slow-moving tropical low dragging moist air down from the equator have created an unprecedented rainfall event for the north Queensland coast, which is far from over.

Key points:

Rain is set to continue until the weekend as Townsville battles a flood crisis
Moist tropical air is converging with south-easterly winds in the Townsville region
The system is stationary, so rainfall is continually centred on the same areas

Hundreds of Townsville residents have been evacuated and thousands of homes have been inundated by rising floodwaters.

Australia’s tropical north is in the midst of the wet season, but even at this time of year this type of rainfall is extreme.

Townsville received a year’s worth of rainfall in nine days, with 1,134 millimetres recorded up until 9:00am on Monday.

Photo:
Forecast rainfall totals for Queensland for Tuesday February 5, 2019. (Supplied: BOM)

The Bureau of Meteorology’s extreme weather forecaster, Grace Legge, said that was a record breaker for the city.

“This is the highest rainfall event in a 10-day period. Townsville has seen over a metre of rainfall in 10 days, which hasn’t been recorded there before,” she said.

“Places like Ingham, Woodlands and even Mount Isa have all seen new 24-hour rainfall records for February.

“It really has been an unprecedented rainfall event. We’re seeing record rainfall that’s causing extreme flooding in some parts, especially around the Townsville area.”

What is causing such torrential rain?

Ms Legge said the heavy rain was the result of a very active monsoon trough and a slow-moving deep low pressure cell sitting to the north-east of Mount Isa drawing in moist air from the Coral Sea.

That moist air is converging with south-easterly winds in the Townsville region.

“You’re getting what’s called a convergence band. So you’re seeing these northerly winds converging with the southerlies, all this air going to one place and causing all these thunderstorms and shower activity,” she said.

“And because this trough isn’t moving, you’re just seeing it continuously stream over the same areas, which is leading to these high rainfall totals.

“The reason that this event is very significant is because this trough has been sitting there for days and just hasn’t been moving.

“Normally you would see the monsoon trough either slowly going north or south, depending on what’s steering it, but at the moment it just doesn’t have anything moving it.

“[The tropical low] is sitting north-east of Mount Isa … so that’s what’s dragging the rainfall in further, and we’re seeing that rainfall inland, which has been good because those parts have been drought affected … but the higher totals are really around those coastal areas and up on the ranges.”

Photo:
Floodwaters surround some homes in Gumlow in Townsville. (Supplied: Meridian Helicopters)

Heavy rain to continue until the weekend

Queensland is not out of the woods yet, with more heavy rain forecast for the next few days.

On Tuesday, the heaviest falls are expected between Bowen and Mackay with up to 150mm possible, but falls between 50mm and 100mm are still expected for the Townsville region.

Ms Legge said it was difficult at this stage to predict exactly when the rainfall would ease.

“Some areas may still be seeing heavy rainfall into the weekend, but it should be easing hopefully on Saturday and into Sunday,” she said.

“Unfortunately for the next few days we’re not going to see that trough move too much.

“It has been slowly drifting a little bit further south so that hopefully means that real convergence zone and higher falls will move a little bit further south of Townsville.

“But it’s still a bit uncertain as to where it will be sitting over the next few days.

“In the longer term it looks like it will be moving a little further north later this week, that low will start moving over to the Coral Sea by the weekend and then will hopefully be moving away from Queensland.”