An East Coast Low (ECL) should form off the NSW coast early next week bringing the potential for torrential rain, damaging winds, hazardous surf and coastal erosion.

These beasts can form quickly, and combine moisture and instability in a powerful package. This one is likely to rapidly develop later on Monday or Tuesday.

As we get closer you may hear terms like 'bombogenesis' or 'rain bomb' or 'explosive cyclogenesis' - they all mean that a low is developing fast and it's going to pack a punch with wind and rain.

Our worst ECL's have sunk bulk carrier ships, and one of them was responsible for the Pasha Bulker running ashore in Newcastle in June 2007 (which stands out in my memory as I was on shift at the bureau at the time).

The key to these is where the low sits.

If it is close to the coast, then those nearby and just to the south have the biggest effects from the wind and rain. Areas well to the south can pick up huge rainfalls, but anywhere north of the low misses out completely, basking in bright sunshine.

If it sits well off the coast, then the effects are less severe - but those on the same latitude as the low and just to the south still have a lot of wind and rain.

The other factor is how long it hangs around for, and how deep or strong the low becomes. The longer they are with us, and the deeper they are, the longer the severe weather lasts.. as the rain keeps on coming.

I'm going to walk through what some of the guidance is modelling as of Friday morning, but please keep up to date as this system develops, as the areas in the firing line will be very dependent on where the low moves, how deep it goes, and how long it takes to move away from the coast.

As always look for consensus across the different models/guidance because when they're all singing a similar tune, and continue to do so from update to update, then we have higher confidence in that outcome.

One Possible Outcome

This guidance is from the Euro model from Friday morning. It has the ECL just northeast of Newcastle on Tuesday night, with a central pressure below 1000hPa.

This puts Newcastle in the firing line, with effects felt through the Central Coast and Sydney.

This has the heaviest rain (for just the one day) at 100 to 150 mm, extending inland to the ranges.

The tight pressure gradient (the lines with numbers line 1000 1002 1004 etc) indicate the wind will be ferocious, and the coastal hazards extreme.

‍

The Euro model's output for Tuesday, showing Newcastle, the Central Coast and Sydney in the firing line

At this stage all the models are not singing the same tune - some have the low well off the coast, others have it loop-de-looping up off northern NSW, and one has it well off the south coast.

Until we get consistency from the guidance, the effects from this beast remain hard to pin down.

But there is the potential for a big impact, so if you are in eastern NSW I'd keep a close eye on the guidance as we get closer.

Jane’s Weather provides hyper local weather forecasting based on the consensus of all the weather models, using Machine Learning and AI to calibrate the forecast to conditions at your farm. We include updates on temperature, rain and wind, along with evapotranspiration for efficient water usage, frost risk, growing degree days and a detailed spraying forecast customised for any property in Australia.