August weather report

Overall a quite dry month with moderate temperatures.  It seemed to be windy, but my data suggests March was more so!

Rainfall

For the benefit of those who can't remember this phenomenon Wikipedia defines"rain" as 

"Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then become heavy enough to fall under gravity."

We did actually get a small amount (32.6 mm) this month.  Much less than both last year and the median fall (61.2 mm).  Surprisingly, of the falls recorded since 1975 this is the only 9^th lowest.

 The shortfall was entirely due to getting relatively little rain when it did fall.  The number of days with more than 0.2 mm was right on average, and last year.

 I have a data series giving the daily cumulative rainfall through a year which I use to calculate a pro-rata estimate of the annual fall.  As at the end of August this is showing a total for 2019 of 578 mm.  If that happens it would be the lowest fall (by ~70 mm !) since the series began in 1975.

Temperatures

The best measure of overall temperatures is the difference between the average temperature for this month and the long term average for the month.  In shorthand, the anomaly.  For August 2019 that was -0.39^oC.  So a little cooler than usual.  (Climate-change denialists shouldn't get excited and cherry-pick that number: it is the first time this year that the monthly average is below the long-term average. Also, over the 25 years of the series the slight trend is for there to be more months per year with above average temperatures than below average.)

This next chart shows how the month-to-date-anomaly changed through the month.  For this longer term series I have used data from the BoM site near the airport.

The table below shows the cross classification of extremes above and below average for the date.

	min above	min below
max above	4	7
max below	12	8

The other general way of looking at the months temperatures is to report the daily extremes, as measured by my weather station at Angophora Dr.

The smallest range of temperatures was 4.8^oC on the 12^th and the largest range 16.5^oC on the 24^th.

Maximum Temperatures

The average maximum for the month was somewhat lower than for 2018 and the longer term average

Minimum temperatures

The average minimum temperature (at our house)was a little above last year and very close to the long term average (both from BoM).

The lowest temperature recorded by BoM was 1.3^oC and at our house 1.9^oC.  It is not unusual to get one reading below 2^oC (ie a light frost) in August with such minima being recorded in 17 of 27 years since 1993.

Humidity

The pattern of daily humidity readings at our houses hows a reasonably moist month especially in the middle of the month when readings were above 60% at 1500 hrs.

During the month the range of humidity through the day is illustrated by the mean rH +/- 1 Standard Deviation.

This shows that the range of rH was quite stable, expected to be between 60% and 90% early in the day dropping to 50% - 70% by mid afternoon.

Looking at my rH values compared to BoM data for earlier years shows this August to have been moister than last year at both standard times, but a little drier for the morning reading.

Wind

Assessing windiness by the amount of vegetation blown down, this was a very windy month!  Charting the daily wind run shows 2 periods of extreme blowiness, and it was the second (from 21^st to 23^rd) which did the bonsai-ing.

Looking at the longer term data I have for wind runs shows an interesting pattern with March 2019 appearing to be even windier.

That is "interesting".  I have looked at the data for March and can see no obvious outlying readings in the data.  Comparing daily windrun with maximum daily gust shows a broadly similar pattern (correlation of 70%).  It's unfortunate that:

• it was the first full month of observations; 
• it was 6 months ago (so I have no great memory of my observations at the time); and 
• BoM doesn't offer daily windrun data for current months.

But I have no objective grounds for amending (or ignoring) the data.  Since I drafted that Frances has commented that when we first moved in (ie including early March) she noticed the wind howling down the flue of our stove.  That hasn't been so evident recently.  This tends to support the data as real, not a figment of of my weather station.

The direction of wind was as normal, mainly from the segments SW -NW.   

The proportion of readings from the dominant section of the compass (~85%) has been higher in more recent months than  in March-April (63%), showing that there have been more fronts coming through from the "West" than low pressure systems perched off the coast.