NSW - THE ACTIVE WEATHER SET TO RAMP UP THIS EVENING WITH SEVERE WEATHER CHANCES OVER THE WEEKEND.

The start of Autumn starting out wet with some areas once again likely to be clobbered over the course of the next week with severe thunderstorms over the inland and severe weather over the coast with persistent onshore winds and heavy rainfall near troughs.


The upper level system passing through the coming 2 days over inland areas is forecast to ease by the end of the week but another upper level low is forecast to move through the state this weekend with yet another round of severe weather expected, severe storms inland and heavy rainfall for those along the slopes and the east coast.


Far western and northwestern areas of the state remain out of the severe weather risks for now with dry air and ridging passing over central areas of the nation. This will cut off the region from any meaningful rainfall chances for now.


It is a very busy period so lets take a look

FORECAST

Rainfall Next 10 Days

Rainfall remains very much above average for the coming 10 days, with two major bursts, one coming through tonight through Friday over the east of the state and the inland areas seeing scattered to numerous showers and thunderstorms. The rainfall will clear over the southern and western areas of the state with high pressure moving in for a period Friday. Showers may persist about the coast with onshore conditions but the rainfall rates lighter. On Friday night there will be another upper trough move in from VIC and this is expected to run into the moisture sitting over the state and widespread rain and thunderstorms is forecast to develop this weekend, some severe storms likely with all modes of severe weather and where the core of the upper low moves will determine the location of the heavy rainfall. As I mention often, we will have to get this current system off the board before we get a better look at the weekend feature. Hoping that there is some moderation in the forecast signals as it could be another decent storm and rainfall event.

FLOOD ZONES SOUTHEAST

The deep east to northeast flow is expected to spread very high moisture levels leading to extensive areas of rainfall. Heavy stream showers and thunderstorms are forecast to produce intense rainfall in the dark blue and purple zones and within this area, some areas are likely to see over 300mm through the period, possibly 500mm in the wetter spots exposed to the northeast to easterly flow along the topography facing east. The rainfall gradient is very tight but moderate to locally heavy rainfall areas will spread to the GDR and stop short just near the ACT. Where the low pressure system moves through, that will spread heavier rainfall further inland and I have drawn that in between Newcastle and Ulladulla for now.


Thunderstorm Forecast Wednesday

Thunderstorms are forecast to increase overnight near an upper trough as that moves towards a deeper moisture source. Thunderstorms over VIC tonight will contract east into the eastern inland of NSW and ACT with heavy falls possible and flash flooding a concern. Along the coast, tremendous rainfall rates and life threatening flash flooding at this stage from around Gosford southwards, but Newcastle and Hunter subscribers down to the Gippsland region and inland to the coastal ranges BE ON ALERT!!!!

Flash Flood Risk This Week

We are looking at significant weather issues relating to intense rainfall along the coast with a coastal low pressure system. We are also looking at thunderstorms over inland areas of NSW and far northern VIC also producing significant rainfall rates and the chance of high impact flash flooding with slow moving thunderstorms. The risk will start to abate from Thursday evening at this time.

HEADS UP SEVERE WEATHER THREAT

Another low pressure system in the upper levels is forecast to approach VIC and NSW this weekend and run into a deep moisture profile and easterly winds. Scattered to widespread showers and thunderstorms are likely to develop with those turning severe through VIC on Friday afternoon with a band of heavy thundery rainfall leading to flash flooding. Then the storm risk breaks out over northern VIC through NSW into southern QLD this weekend with dangerous thunderstorm activity possible with all modes of severe weather possible including giant hail and destructive winds (tornado activity) over parts of the east. Heavy rainfall also looks set to redevelop along the coast with intense rainfall rates but determining who is in line for that remains to be seen so stay weather aware.

DATA - Refer to video for more information and for the daily run down


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

There is more analysis in the video, but the areas of concern to watch have been well forecast ahead of time, and we will start to see them unfolding now. So that being the flood event for the NSW coast and adjacent inland, the approach and passage of TC Anika and the severe weather potential for inland areas with flooding. We may see another wave of low pressure in the upper levels on Friday drive severe weather for eastern SA, VIC, NSW/ACT and southern QLD this weekend with follow up severe storms. The remainder of the nation away from the southeast, east and northwest looking at seasonal conditions. In the medium term you can see the impacts of the positive SAM phase.

00Z GFS - Precipitable Water Values - Next 2 Weeks

The very deep moisture profile is expected to dominate for the coming week over the northwest and over the east and southeast with a dynamic atmosphere in both locations leading to the above average rainfall. Elsewhere, the drier air is planted firmly over the southwest of the nation and in pockets of central and eastern inland areas on the backside of low pressure moving through the east. The pattern may begin to shift in the medium term but at this stage, it looks like the models are keen to keep the easterly wind bias in place.

00Z GFS - Rainfall Accumulation - Next 10 Days

Refer to video for more details

00Z GFS - Rainfall Accumulation - Next 2 Weeks

Refer to video for more details

A closer look in - the wet weather in the east, as we have seen in recent days has been under forecasting the rainfall so expect to see heavier falls than what is shown here and what is forecast in specific forecast zones.

More coming up tonight with a look at all things modelling and rainfall after 9pm EDT.




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