Updated: Mar 24

There are 2 parts to the weather evolving over the east which could bring the chance of flash and riverine flooding coming back to areas which were clobbered earlier this month. Now this is not unusual, it is the wet season over the east coast of NSW and this IS NOT A RAIN BOMB!

Standards have dropped since I have left TV!

Anyhow....I digress. The weather, turning more unsettled through today and into Friday with pockets of showers and storms already producing moderate to heavy rainfall in central and northeast NSW. The remainder of eastern NSW from about Cooma north through Canberra to Orange up to Dubbo and near Lightning Ridge, carries the chance of more showers and storms developing this afternoon. These will be more widespread up over the northeast and central parts of the state.

This weekend, unsettled. Areas of rain with local thunderstorms over the northeast and about coastal areas from north of Moruya to about Yamba. Some areas on the extreme coastal fringe could see 100mm of rainfall in quick time so be aware of that.

The flow pattern becomes more mobile over the weekend and the showers with moderate to heavy falls will then begin to move inland and this is where we could see daily falls of 50-100mm across the Northern Rivers, Mid North, Upper Hunter, Hunter, Central Coast and Metro regions of NSW. Moderate falls of 20-50mm down the Illawarra, Shoalhaven and into the South Coast with this first burst.

Next week there has been evidence of another trough developing on the northeast flow that establishes with high pressure moving into the Tasman Sea with more widespread rainfall developing. It is a low chance of occurring but the GFS and Euro have been very expressive across the back half of next week.

Lets look at the first system


Rainfall Next 5 Days

Rainfall as mentioned becomes more widespread this afternoon with an expression of convection underway over central and northern parts of the state and this will start to drift east this afternoon. Locally heavy rainfall is expected across parts of the northeast and east coast this evening. Some areas could see flash flooding overnight and into Friday with slow moving showers and storms about the coast. Tomorrow afternoon, the flow pattern starts to freshen and then we will see frequent showers moving inland of the coast and the rainfall intensity picks up Friday through to Monday evening. 3-4 day totals could exceed 100mm in many areas along the coast and spot falls of 200-300mm cannot be ruled out during this time. The heaviest rainfall expected over the coast and adjacent coastal escarpment between Sydney and Yamba. Inland areas could see moderate falls from thunderstorms and there is some evidence that more widespread rainfall could extend into the Central and Northern Tablelands over the weekend, but confidence is not especially high so watching those radar trends closely in the days ahead. Dry weather for the south and west at this time.

Rainfall Next 10 Days

Overall the rainfall looks to come in 2 waves, the first 5 day event as spoken about above, and then another potential for showers to increase with another trough stalling out over the NSW coast. If a high can sneak in under this feature we could see northeast winds feeding the trough and this is a more dangerous set up for heavier rainfall across the coastal areas. There is a higher chance of the heaviest falls with this feature to be south of Sydney.

Severe Weather Watch - Friday through Tuesday

Watching very closely the emergence of the upper level low moving into western NSW during Friday and how that interacts with the moisture and the existing trough sitting over the northeast of NSW and southeast QLD. Could see a rather expressive period of convection and given the dynamics, the chance of severe weather with storms is elevated over inland areas. Along the east coast, in east to northeast winds feeding the system, we could see heavy showers and flash flooding initially, and deepening on the rainfall coverage and the performance of the troughs together, there may be intense rainfall returning to parts of the coast. The most likely areas would be the extreme coastal fringe between Sydney and Yamba at the moment. The severe weather contracts into the northeast and east of the ranges by next week. The most active severe weather will be over areas south of about Chinchilla in QLD.

Riverine Flood Risk - Friday through Tuesday

The catchments are still very wet even though we have seen an absence of rainfall in recent weeks. The rainfall forecast will be moderate to heavy over a number of days and over time, the catchments will respond to this rainfall. Falls of 100-200mm are possible in the coming period in scattered pockets along the extreme coastal fringe and falls of 50mm an hour with thunderstorms are possible in all areas highlighted here. This may trigger minor to moderate flooding to redevelop along the coast. At this stage the amplification of the event is no where near the levels of the previous event but once again, riverine flooding is a significant risk for catchments devastated by the early March event. Remain weather aware through this region.

Flash Flood Risk - Friday through Tuesday

Flash flooding is a significant risk with thunderstorms with the upper level system moving in from Friday if not Saturday, into the moisture and stalled boundary over the north and east of NSW. The two will combine to bring scattered storms, some severe, with heavy rainfall leading to flash flooding a significant risk. From Thursday, there may be thunderstorms along the coastal fringe and streams of heavy showers floating about between Batemans Bay to Yamba that could see some coastal areas net 50mm in a couple of hours. Thunderstorms over the weekend across central, northern and northeast NSW could drop 30-40mm in an hour with the coverage contracting eastwards during the weekend into early next week.

The pattern is complex and the expansion or contraction of risk areas is possible in the next 2-3 days. I will have further details in the state based forecast this evening.

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