Weather Report December 2023

 We are now supposedly in an El Nino period which according to the BoM 

"In Australia (particularly eastern Australia), El Niño events are associated with an increased probability of drier conditions." 

That usually also means warmer temperatures, as explained in this BoM sheet,  in which case we have 1 out of 2!   Another very wet month with very warm daily minima and mild-warm maxima.  (I haven't looked at the other attributes of El Nino listed by BoM, although in a light-hearted way will note that snow depth in Mallacoota was, as usual, 0.0mm.)

I will do an annual report in the next few days

Rain

We ended the month with 187.4 mm of rain (275% of the median) with non-trivial amounts falling on 12 days. 

In terms of comparison over time we are well over the median and the fall in December 2022.   

The total fall was the second highest recorded for a December since 1976, beaten only by the 211.8mm recorded in 2021.  The variability between years is obvious and there is no trend in these data.

Temperatures

The overall assessment of temperatures can be represented by the difference between the average temperature for the month and the long term average for the same month, referred to as the anomaly.  The next chart shows how the value of the anomaly developed through the month: in effect warming early in the month and then cooling towards the end.

I am compiling a time series of values of the anomaly since I started to calculate this statistic in 2020. I have also compiled a 12 month moving average (to remove seasonal factors) and applied a 4th order polynomial trend to remove 'noise' (or random fluctuations).  This appears to reflect the passage of the last 2 years of La Nina rather well.

Another way of looking at the overall temperature is by comparing the daily extreme temperatures with the averages for that day of the year.  

The chart has a few interesting features:

• The current maximum series fluctuates considerably reflecting the passage of weather events, while the current minimum series is more consistently above the long term average;
• There is (as would be expected) much less fluctuation in the long term series.
• Both the long term series show an upwards trend though the month, probably achieving statistical significance in the case of the maximum series.

Minimum temperatures

The average minimum temperature for the month was 16.10C, the second highest value for December since my series commenced (the highest value of 16.22C was recorded in 2018.  Not surprisingly the 2023 value was well above those for 2022 and the mean.

Noting that all months since July have been above the long term mean offers an indication that at least some aspects of El Nino have been evident for a while.  12 of the daily minima were more than 1 Standard Deviation (SD) above the long term mean for the month and a further 12 were above the average but less than 1 SD above the monthly mean.  Only 7 days were below the mean minimum for the day.

A time series of average December minima shows no significant trend.

Maximum temperatures

The average maximum temperature for the month was 23.89C above the mean but well below the highest average recorded (25.3C in 2019).  It was also above the 2022 value.

It is a trifle problematic to make large statements about the older data (based on BoM data for the airport site, adjusted to make them more comparable with my Weather Station - WS - data).  Instead I offer  the chart below showing 5 years of data from my WS.  It is interesting that the only year with a hotter end was 2019.

Humidity

One word: muggy!  Another word: soggy.  Humidity levels were high through the month with only 2 days recording humidity below 50%.  The chart of readings at the 2 standard times is rather unusual with the 2 lines being much closer together than would be expected.

For both standard times the average relative humidity across the month was above average and the value for 2022.  THat applies particularly to the 1500hrs reading.

I wondered if there was a link between amount of rain and humidity.  The correlation coefficient was not great, at 42.8%, but the chart does show a vague coincidence of higher humidity (as measured by the daily minimum rH ) and rainfall.

Wind

Most days were reasonably calm although the passage of systems did give periodic breezy days (coinciding in most cases with spikes in maximum temperature).  The windiest day, with a run of 310km, was the 4th longest run of 2023 and the 32nd longest (of 1784) recorded at my WS.

Overall the month was quite calm with average run below the values for 2022 and the 5 year average.

Sundry snaps around Mallacoota

 This is more or less gathering together some photos I have taken over the last couple of weeks.

On going to the poo pits for my regular survey I was surprised to see a rather pale wader flying around above pond 2.  I was eventually able to get a reasonable image which has been identified as a Marsh Sandpiper: the first record in the District and I think the 7th in the Shire.

Roadworks are in progress along Lakeside Drive after the floodwaters dropped.  My guess is the level of the Lake was about 2m above 'normal': this was the highest I remember seeing it, but some old-timers commented about it once reaching the steps on the Bakery.

The boardwalk was fixed up very quickly considering how badly it appeared to have been damaged, and the gate was removed shortly thereafter.

A Koala was not at all fussed.

I went to Shipwreck Creek some days later to see the state of play there.  I have no idea how deep the crossing was but decided that  it was not worth experimenting.

We went to the Eastern Heath instead and found a few interesting items.  A Jacky Dragon posed obligingly for a photograph.

A Large Tongue Orchid (Cryptostylis subulata) beside the path through the heath.

Back at home, there is a fair bit of flowering going on.  Our Magnolia in particular is putting on a lot of flowers.

The bronze Leptospermum is just getting started.

A daisy of some sort.

A cypress: interesting pattern of leaves,

The gulls have nested here before.  If the weather is at all warm the eggs (or chicks) cook!

A sad jetty.  I suspect they didn't use the correct screws to fasten the bearers.

On going dampness

 This is initially a set of photos from around the District showing the flooding.  They begin on 1 December at the bottom of Angophora Drive.

The Goodwin Sands used to be there somewhere!

Now to second of December.

The next three from Genoa.

This chart is at 0700 on 3 December.

November 2023 Weather Report

 In terms of temperature the month averaged to being warm, but this was largely due to high daily minima (usually overnight temperatures holding up).  The outstanding feature of the month was the dramatic rainfall caused by an East Coast Low in the last two days of the month, making it the second wettest November on record.

Rainfall

In essence a month of two halves.  From the 1st to the 19th my Weather Station (WS) recorded rainfall on 2 days, totalling a miserable 2.2 mm.  From the 20th onwards the WS recorded rain on 10 of the 11 days, falls above 5mm on 5 days.

As expected this total is way above last year and the median fall for November.

A time series for Novembers shows the result to be outstanding (but not unprecedented)!  The values for 1981 and 1982 come from Gabo as BoM has no data for those months.  (The highest rainfall for any month shown by BoM for the Airport site is 440mm in April 1989.)

Apart from the sheer amount of rain in the last 2 days of the month the contrast between the steady, modest-rate falls until 1400hrs on the 30th and the series of squalls which followed was dramatic.  

In terms of outcome, the closure of the Genoa Rd by a landslide has had the greatest impact.  There has been a fair amount of flooding around the area due to the rising level of the Lake.  This seems to have been a 'perfect storm' combination of heavy rain, high tides and an onshore wind.  A couple of photos:

Lakeside Drive at 0800 hrs on 1 December.

Where have the Goodwin Sands gone?

Temperatures

My usual measure of the overall temperature is the difference between the average temperature for a current period and the long term mean of that measure: this is the anomaly.  For November looking at the average temperature the overall value is +0.95C.  After a very cool start to the month followed by a warm spell (see below) the anomaly mainly resolved to close to +1C.

Most of the extreme temperatures were moderate: they are discussed in the following sections.

Minimum temperatures

The average minimum temperature for the month was 13.77C well above the long term mean of 12.27C, as shown in the following chart.

An overall time series of minimum temperatures is not of great assistance as it varies greatly from year to year.  Instead I have compiled a set of annual series for readers to contemplate.

I have also examined the daily values for significant variation from the long term mean.  In November there were 9 days in which the minimum was more than 1 standard deviation above the long term mean (but no occurrences of minima more than 1 SD below the mean).  Indeed there were only 6 daily minima below the average for that day.

Maximum Temperatures

The average minimum temperature for the month was 22.53C slightly above the long term mean of 22.12C, as shown in the following chart.

The set of recent average monthly maxima are interesting in that they show the maxima for the colder months to be above average, but for the last two months have moderated, probably due to cloud cover.

6 daily maxima were >1SD above the long term monthly mean and one day (11th, maximum 34.3C) was >2SD above.  only one of the significantly high maxima coincided with a significantly high minimum, meeting my definition of a Hot Day.  Due to lack of consecutive Hot Days there was not a Heat Wave but I considered 7th - 11th and 21st to 26th as Warm Spells with maxima and minima above the average and several values for one of the indicators significantly so.

Humidity

Overall a somewhat sticky month, with both 0900hrs and 1500hrs relative humidities well above the average for those standard times.  From the 22nd onwards relative humidity was always above 70% for both those times.

Wind

Normally November is one of the windiest months but the last month was, overall, relatively still as far as my WS measured it.  My WS has poor exposure to wind, especially from the South and East, and  unfortunately the BoM publishes (at no charge) very little information about wind.  Comparing the maximum daily Gusts from the two sources shows they correlate "fairly well"  (correlation coefficient of 0.52).  

There were a couple of windy days early-mid month, and again in the East Coast Low period, as shown in this chart of daily runs from my WS.