September 2021 Weather Report

 My overall summary for the month is mild temperatures, calm(ish) winds and pretty damp!

Rain

We had non-trivial (ie >0.2 mm) rain on 12 days of the month.  Including the trivial amounts gave a monthly total of 91.2 mm.  This is 139% of the median September fall and 122% of the mean fall.  Another way of expressing this is to say that of the 41 previous years of Mallacoota records only 11 had higher September falls.

Not surprisingly, the fall was higher than 2020.

I was somewhat surprised to find that the rate of fall (75.2 mm/hr on the 30th) was the 20th heaviest rate rate I have recorded here (out of 963 daily records for all months).  It is the second heaviest fall (out of 90) in September records.

By the end of September the total for the year was 895 mm compared to a median YTD of 660mm and a mean YTD of 703.  The prorata estimate for the year as a whole is 1198 mm: it seems almost unbelievable that we will end up with less than 1000 mm for the year.

Temperatures

The overall anomaly was 0.3C.  The month started off quite warm but then gradually cooled, particularly in the second half of the month.

The next chart compares the BoM extremes for each day with the long term average for the day.  There were few days in which both minimum and maximum were above or below average (the number of warm days (both above) was particularly low).  The common situation was minimum above average and maximum below 

As should be expected my WeCather Station (WS) shows a similar pattern.

Minimum temperatures

The average minimum temperature at my WS was 8.9C, well above average, but below the value for 2020.  Looking at a time series there is no significant trend in the data.

Maximum Temperatures

The average mamimum temperature at my WS was 17.9C, below the value for 2020 and the long term average (adjusted for the small difference between the BoM Site and my WS) .  Looking at a time series there is no significant trend in the data.

Humidity

As would be expected in a month with rain on 14 days humidity readings were quite high.

For the 0900 reading values were on average higher than both the average and the value for 2020 (all data from my WS).

For 1500hrs a similar situation applied, with the 2021 reading more significantly above the average.

 I was struck by a very low reading for 1500 hrs on 11 September so plotted the hourly values for 9-11 September.  In the chart I have also shown the hourly temperature readings: the two series are almost  mirror images, with a correlation coefficient of -0.95!

Wind

To overcome the very sparse free data on wind ( I presume BoM sees the main users of this data as the airlines, who can pay for it) I have restricted the following charts to the 3 years for which I have WS data.  The first chart is in the standard format (this year, last year, average) for average daily run.  This shows September 2021 to be below both the average and 2020. 

Looking at the numbers it appeared that 2019 was generally the highest of the three years and 2021 the lowest.  The seasonal pattern is generally similar (as far as can be calculated with missing months in 2 of the 3 years.