October 2019 Weather Report

Overall the month was about on average for mean temperature and 15% below median rainfall.  Humidity was higher in the morning but lower in the afternoons.  It was less windy than past data would suggest and the wind came more from the East than has been the case in past months.

Rain

I recorded 50.2 mm for the month (BoM: Mallacoota 52 mm; Gabo Island 40.4). As noted above this is below the median for October but well above October 2018.

Longer term rainfall analysis

Using a pro-rata method to estimate the possible annual rainfall given falls to the end of the month comes up with a result of 578 mm - a slight improvement on the situation at the start of the month.  

Someone recently mention a 3 year drought so I have examined the situation using rolling averages for 12, 24 and 36 months.  That is summarised in the following chart.

This shows the local peak of the 36 month series as October 2016 - exactly 3 years ago!  The 12 month series shows a period of decline starting in April 2015. 

The longest period of decline in the 12 month series is from 1989 to 1995 - close to 6 years!  I hope we don't break that record. The 12 months from June 1994 to May 1995 average 45 mm per month: other months in 1994 - 95 have more rain bring the calendar year averages up to more healthy levels.

Temperatures

My overall summary of the temperature is the difference between the mean temperature for the month and its long term equivalent (in both cases using BoM data for Mallacoota).  For October that ended up at +0.04^oC - effectively at the average.  The development of that anomaly through the month shows an early period of warmth, cool through most of the month and a warm sting in the tail.

Looking at the relationship of the daily extremes to the average values for that data shows the most frequent situation was for both measures to be below average.

Another way of showing the temperatures is the daily temperatures recorded on my weather station on Angophora Drive.

 On looking at that chart I was struck by the range of temperatures on some days and the day to day  variation in the range.  I charted that together with average range for the date and the values for 2018.

Eyeballing that graph it appears that the ranges seen had some unusually high values and the level of variability was higher than most years.

Maximum temperatures

The highest maximum recorded was 34.9^oC on the 31^st.  The monthly average maximum was 19.9^oC.  This is above average, but a little cooler last year.

The series since 1993 does not show a significant linear trend.

Minimum temperatures

The lowest minimum for the moth was 5.4^oC on the 13^th.  The monthly average minimum was 9.8^oC..  This is slightly below average and last year.

Again no significant linear trend in the series.

Humidity

The morning and afternoon values are generally quite similar with few morning fogs and some quite low values towards the end of the month.

The morning value is higher than last year and the history shown by BoM while the opposite is the case for the afternoon value.

Wind

Although it appeared to be quite a windy month records from my WS do not confirm that.  (The BoM has several days missing for their only indicator (maximum gust) for Mallacoota so is even less helpful than usual for wind!)  In addition the windrun was lower for October than for September, which goes against the few snippets of past data available from BoM.

As there was a disjoint between my expectation and the observations I looked at two measures of "windiness" and the pattern is broadly similar (correlation coefficient 0.64) so conclude that my WS is not failing.

Possibly the most surprising observation for the month is a relatively high (22%) of hourly wind records coming from the ESE.  

Looking at previous WS records it seems that this increase in winds from ESE is balanced by a decrease in those from the NNW and N directions.  As the WS has not changed position (nor has the wind vane been interfered with) I can only assume this is a seasonal shift.