Low, and on the East Coast

This post is about the weather event of 26 to 28 July 2020.  I have done another post with some images of the impacts of the rain etc.

I have used the title of this post since the BoM seems reluctant to call the event an East Coast Low (ECL).  They have a fact sheet about such events and this event seems to tick (at least) most of the boxes for an ECL and doesn't match any of the other possibilities in that sheet.  Discussion (by meteorologists) on a forum I follow seems to conclude that this is actually an ECL - they have information that the crucial attribute (of upper level events impacting on surface level events) has happened.  

Whatever one calls it we had a lot of rain - 104.6 mm and counting - such that we are now (0640 on 29 July) 25.4mm (1 inch in old money) above the pathetic total in 2019.  Doing a pro-rata estimate for falls to date my guesstimate for 2020 is 960 mm, the highest since 2016.  

I will begin with a chart of the hourly rainfall from midnight 25 July to 0700 on 28 July.  (A small amount has fallen since then but it doesn't greatly change the picture.)  

Another way of looking at this is the cumulative amount that has fallen.

The rain was quite steady with only a couple of spikes in the rate.  Knowing that my WS has recorded some squalls well over 100 mm/hr I originally rated them as quite modest at around 70 mm/hr.  However looking at the detail shows these to be about the 16th and 17th heaviest rates (out of 16,000 observations)

Looking at the wind is interesting.  As always I am a little tentative about wind readings as the wind exposure of my WS isn't ideal.  

There didn't seem to be any outrageous gusts (37 kph was the strongest gust and the longest hourly run was only 11.2 km).   However the direction of the wind produces a somewhat strange chart.  In the lead up to the low getting down this way any of the wind observations are from the NNW (bearing 337.5 degrees).  However once the low arrived the wind settled down to ESE (112.5 degrees) with a few gusts from the SW (225 degrees) presumably reflecting the passage of embedded cells. 

A key factor of low pressure systems ins the low pressure (duuhh).  This chart shows the pressure dropping from around 768 mm until about midnight 27 July when it settled down around 758 mm for the rest of the period of recording.

The centre of the system was somewhat North of us.  By way of example, Ulladulla, 260km NNE of Mallacoota, copped a real downpour.

A chart of the accumulation shows the steady rate of rain.

The ultimate impact of the rain is to boost the inflow to the Inlet.  Here is the BoM gauge at Genoa River Gorge.  The rise was from 075m to 2.40m: as indicated it was above minor flood level from several hours.