NSW - SHOWERS INCREASING WITH THUNDERSTORMS TURNING WIDESPREAD THIS WEEKEND OVER THE NORTHERN INLAND

The weather after a few dry and sunnier days has turned, after all this is the wet season for the east coast and this should be expected at this time of year. Severe thunderstorms are ongoing for the northern inland and extending into the northeast and this will be the case in the coming days as profiled throughout the week. A fairly unsettled period is on the way for the north, central and northeast inland.


Thunderstorms over the inland in the coming 2-3 days could produce some locally heavy rainfall which may lead to flash flooding.


Further south, cloudy skies along the coast and the adjacent coastal inland with some showers developing this evening with some of that turning moderate to heavy about coastal areas in the absence of thunderstorms. Some flash flooding is possible in the coming days.


Now the confidence is fairly good on heavy rainfall continuing through the weekend and into next week along the coast that will lead to riverine flooding developing as the upper trough and surface trough along the coast slowly move through. The weather not easing until about Tuesday.


Looking further west, conditions are forecast to remain dry, mostly sunny and seasonal with cool nights in the drier and clearer skies.


There may be another trough next week that moves through the southeast and east of NSW and this could once again interact with the onshore wind flow leading to another round of moderate to heavy showers and potential for further flood risks for the east coast, but that system is out there in the back of next week and currently carries low confidence.


I am not seeing much rainfall opportunity for the western and southern areas of the state at this time.


Lets take a look

FORECAST

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.

Thunderstorm Forecast Friday

Thunderstorms are currently ongoing over the northeast and central parts of NSW and will continue overnight and into Friday. Storms could be severe at anytime but more likely during the afternoon and the evening. Storms may produce heavy rainfall leading to flash flooding and damaging winds as the main concerns for now. A low chance of coastal thunderstorms with onshore winds converging with northwest winds from the inland overnight south of Sydney.

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.

DATA - Refer to the video for further information and it is critical to keep check of the data sets to understand where the next major weather events are emerging from outside of this period. It may be quiet now but I am all about preparation and ensuring that information is shared with you as soon as it is available.


00Z GFS - Surface Pressure Pattern and Rainfall Distribution - Next 2 Weeks

The latest GFS is now moving more into line with the Euro and we are starting to see the models converge on the idea of where the driest weather will be and where the heaviest of rainfall and severe weather potential will be. As pointed out in the video, the west, north and east of the nation carry the higher risk of seeing widespread rainfall with above average rainfall possible. Over the east, the rainfall could lead to flooding along the NSW coast. Over the northern tropics, watching the emergence of the tropical low over the weekend and what that does next week, though the latest GFS is in line with the Euro and produces a system that deepens into a cyclone near to the north of the NT and then heads west bound. That will be a feature to watch. And in the west, the remains of Charlotte still hard to pin down but there is now growing evidence that the heavier rainfall for the west may actually come next week with a deeper moisture developing offshore the northwest of the nation being drawn southeast in the wake of Charlotte. If you are in the southern NT, SA, western and northern VIC, southern and western NSW and western QLD., it will be likely dry for a while.

00Z GFS - Precipitable Water Values - Next 2 Weeks

The moisture distribution is unchanged from this morning where we see the moisture damming over the north and east in the current climate drivers allowing these areas to remain humid and the threat of above average rainfall to develop remaining also quite high. The west seeing constant moisture streaming in from the Indian Ocean via the jet stream. Also the moisture over the east coast will move into an upper low which will trigger severe storms in the short term, this likely to move out next week. Dry air stays put over the remainder of the central and southern/southeast inland for the next week with very little change expected to this.

00Z GFS - Rainfall Accumulation - Next 10 Days

Refer to the video for more context and analysis

00Z CMC - Rainfall Accumulation - Next 10 Days

Refer to the video for more context and analysis

00Z GFS - Rainfall Accumulation - Next 2 Weeks

Refer to the video for more context and analysis

A closer look in - this forecast is very low confidence into the medium term and I want to stress that what the models are expressing at the moment is more high amplitude synoptic patterns associated with large thermal gradients and deep moisture content. This is what causes havoc on the models so watch closely in the coming days.

More coming up from 9pm EDT with a look at the models and rainfall, I will only share information that is in reasonable agreement as too much is too confusing and I only want to share what is plausible at this time, so stay tuned for that.



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