Weather apps such as WeatherZone and WillyWeather are calling for the seas and swell to rise overnight on Saturday night reaching a peak at dawn on Sunday of 6.4m from the northeast.

The apps are also calling for heavy rainfall at Narooma and the rest of the Far South Coast with 25-50mm today Thursday, 25-50mm on Friday, 35-50mm on Saturday and whopping 50-100mm on Sunday.

These huge seas and heavy rain if the forecasts are true could do some serious damage or at least shift the sands of the beaches around the Far South Coast. 

Neale Fraser, senior bureau forecaster has told the Sydney Morning Herald that falls could reach at least 100mm at Sydney from Saturday to Monday with totals dependent on how long the low lingers just off shore.

Mr Fraser said the east coast low may develop multiple centres, bringing rain far inland.

"There's a big strong high over New Zealand," he said. "The whole system is quite slow moving...This low will be around for a few days." 

East coast lows are most common in June, which is why the month is Sydney's wettest with an average of 131.9 mm, according to Bureau statistics going back to 1858.

Many sporting activities are likely to cancelled if the rain comes as predicted, while big swells are expected along the coast.

This weekend's rain is being fed by moist airflows streaming across the continent from north-western Australia. Also contributing to the intensity will be the warm waters off NSW, Mr Fraser said. Sea-surface temperatures off Sydney remain at about 22 degrees.

Rainfall totals may exceed 200 mm in coastal regions over the next eight days according to the bureau's forecasts. Click here to read the whole SMH article 

Click here to see photos of a previous East Coast Low at Narooma

So what exactly is an East Coast Low? The Blackheath Weather website has an excellent explanation:

One of the most exciting weather events for cold weather lovers is the East Coast Low. These earnestly awaited, maritime gifts typically occur in autumn or winter with an average frequency of one or two per year. It seems that their yearly occurrence peaks every ten years or so (L.C Hopkins and G.J Holland) when up to six ECL's can develop in a given season. So why is this weather phenomenon so interesting to cold weather lovers? Its produced some great snow events over the years and we all sit around waiting patiently for the next one. 

A typical precursor to ECL development is when a large pool of warm water breaks out of the tropical ocean and heads south, along the east Australian coast. Such an event may repeat itself over a course of weeks throughout the winter period. Added to this foundation, an upper level cold pool needs to move in over a surface trough that is situated north of a strong subtropical high pressure system. In the image immediately below, you can see the surface patterns developing to assist potential ECL development. The surface pressure trough marked with the "L" north of Sydney sits atop a subtropical high pressure ridge that is centred over Tasmania, marked "H" and extends over New Zealand. 

Night-time development is preferred for East Coast Lows as the strong temperature gradients between the cold land (especially in mid winter) and the warm ocean eddy strengthens the system. Further intensification arises as warm ocean air is forced over the cold land air, releasing latent heat as cloud and rain forms. With the high ground of the tablelands just inland from the coast, the associated forcing can really enhance development of the low if easterly winds are directed onto the coast. Usually, if/when the ECL moves away from the coast, it weakens rapidly. Upper level support for ECL's can be in the form of the sub-tropical jet stream where the divergent, poleward exit region is of assistance. Some of the most severe forms of ECL's can produce winds in excess of 150km/h and very heavy precipitation.

Rockfishing safety alert

Just in time to spoil the weekend fishing...coastal conditions look like turning very rough Saturday and continuing into next week.

A developing east coast low and frontal system will affect coastal fishing, offshore, on any exposed or effected coastal rock platform, and many coastal beaches. 

On Saturday seas of 3 metres and swell of about 4 metres will affect the entire coast (except slightly less on Batemans and Eden coasts). Conditions get worse on Sunday with swells of at least 5 metres on Sydney coast and all districts south, and around 6 metres for Coffs and Macquarie coasts.

Large and powerful surf conditions are expected to be hazardous for coastal activities such as crossing bars by boat and rock fishing. 

Check local conditions by going to BOM district forecasts at http://www.bom.gov.au/nsw/forecasts/map.shtml

Stay safe, always watch the local conditions before fishing and never turn your back on the ocean.

Malcolm Poole, Fishing Safety Officer

Recreational Fishing Alliance of NSW