Tuesday, 3 October 2017

Weather Report September 2017

This is the final version of the table which appears in the Gazette.  The only difference to the printed version is a slightly higher average temperature, as September 30 was slightly warmer than the average day in the month.
Readers may also be interested in this post which looks at the question "is the weather "normal"/"  Despite a few extremes being seen this month my conclusion is that temperatures are within expectations but the rainfall seems to be very variable.

In summary it was a another very dry month, as expressed both by rainfall and relative humidity, with strong winds.  Temperatures were slightly warmer than usual.

Rainfall

I shall not make many of the relevant comments such as "What is this concept called rainfall?"  For the 4th month in a row we recorded well below average rainfall.
 The rainfall Year To Date (YTD) shows the ugly story with the aggregate barely struggling above 50%.
Extrapolating the YTD forward gives an annual total of 378 mm which would be 31mm below the previous lowest recorded in this area. 

If one wished to dig a nugget of optimism out of the current situation, the record low fall recorded by BoM for the ANBG was 328mm (in 1982).  (Of that total 150mm was recorded in March.)  So it could be worse!!!

Temperature

In essence a series of warming periods followed by a rapid drop as a front comes through.  This will be looked at a bit more under wind, since wind and a drop in temperature were all we got.  No rain.
The average maximum was a smidgin (sorry about the technical term) above the long term average.  However the hottest day (23rd) reaching 29.2oC  was the hottest September day recorded in the area by about a degree.
The average minimum temperature was well above the long term average but below the level recorded in the very cloudy September 2016. 
 I have talked about some high minimums recorded in September 2017 in this post and note that as foreshadowed the temperature in the evening of the 24th did drop well below the overnight minimum recorded that morning.

The final element of temperature is the number of frost days.  Taking the broad definition of frost (below +2oC) aka  a Ground Frost, the month underperformed with 75% of the average number of frost days.  However going for days with a hard, or air, frost of below 2oC the result was 20% above average.  So when it was cold it was REALLY cold.

Humidity

However one looks at it the month was not humid.  I guess that is what happens when the wind has blown right across the continent!  The average 3pm humidity for the month was very low at 40%. (Note that data for 2016 was not collected due to a stupid by me wiping it from the weather station!) 
 The low value is well demonstrated by these daily readings, with values of 17% on the 23rd and 24th!

Wind

I am normally reluctant to make big calls about the wind recording as my site is not well set up to record wind.  However it seemed, subjectively, to be a very windy month, even by the standards of the gales of the equinox expected in September.  And so it is shown.  

My usual measure is the average maximum hourly gust over the month.  That was well above the long term average and other months of the year.
 I created an average for the 2 years for which  do have wind data for September and as expected this shows that most days had stronger gusts in 2017 than the other years.

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