A moist onshore airstream which has been identified on modelling over recent days is now coming to fruition for southeast NSW and eastern VIC with a trough sitting offshore, promoting showers and thunderstorms offshore which turns to areas of rain onshore.
A deep upper low over northern NSW is helping to draw in this moist onshore airmass, triggering the widespread rainfall and thunderstorm activity.
Satellite imagery for May 5th 2021 showing that moist onshore airstream dragging in the moisture from the Tasman Sea.
The rainfall is expected to continue being locally heavy. Overnight we saw falls of 100-150mm in the Bega Valley and scattered falls of 50-100mm recorded up and down the coast south of Sydney. Soaking rainfall of 20-30mm recorded to the GDR which is very welcome after a dry four weeks.
Rainfall in the 24hrs to 9am on May 5th 2021.
Rainfall is expected to increase once again across these regions with the approach of a low from the north, which will evolve out of the upper low moving offshore. This low is expected to weaken as it moves south through the Tasman, but it will squeeze a stronger easterly flow onto the coast as it moves south, once again lifting rainfall totals.
100-150mm of rainfall are possible about the usual wet spots, it may lead to some minor flooding come Friday for some catchments, but no widespread inundation is expected at this time.
Euro Model 18z run May 5th 2021 - Rainfall until Friday morning.
So with that, the flash flood risk will remain elevated for parts of the coast, especially those living about the South Coast, with heavy falls connected to thunderstorms posing the greatest threat.
Some of this rain may drift into extreme East Gippsland during the next 36hrs, but it looks like the trend is keeping the bulk of the heaviest falls over the NSW side of the border.