May (and Autumn) 2025 Weather Report

Frances commented on the evening of 31 May that "Tomorrow is the first day of Winter." so it behooves me to comment on the summary of the last three months representing Autumn (or as those from the Evil Empire across the Pacific call it, "Fall").

Autumnal Review

My Weather station has now recorded data from Angophora Drive for 7 Autumns.  These are summarised in the page 'Seasonal Summaries' in this Google Sheet.  Summarising further:

• The average daily minimum temperature was the warmest, by 0.3C, of the 7 seasons.  It was 1.01C above the average of the 6 earlier years.
• The average daily maximum temperature was the warmest, by 0.9C, of the 7 seasons.  It was 1.31C above the average of the 6 earlier years.  
• (In both cases the 'runner up' was 2019.)
• Although the station is not well exposed to wind it is interesting that the wind run for the three months is the second lowest of the 7 years.  (This may reflect growth of garden shrubs rather change in the weather!)
• Rainfall was the second highest (90 mm below 2022) and still 150mm above the average.

Monthly material

The month was very wet (only 3 of 46 previous Mays recorded more rain) and warm (temperature anomaly of +1.14C.   Relative humidity was at the high end of the 7 years for which I have data (but not extreme - whether examined for the standard times or for the average of the month as a whole.  Wind run was very low: possibly reflecting a higher than usual proportion of BoM wind records from the Eastern half of the compass, from which my WS is fairly sheltered.

Rainfall

In a post on 23 May to the Facebook Group I commented:

"I was a little surprised yesterday morning at how little rain was being recorded on my WS compared to what I was seeing. On going to check the WS I found that the rainfall collector was full and the filter was blocked by green slime. Never had that happen before in the 12 years I have had the device. Removing the filter let the liquid run through, tipping the cup 10 times!

Comparing the WS records with my Nylex suggests it has been missing about half the falls in the last few weeks. (I am quite happy with records to the end of April.) A comparison with BoM records for the Airport and Gabo, and information from Marty suggests that doubling my records for 18-19 May will give a fair estimate of reality so I have done that. Recording immediately started to match what I was seeing."

So it is possible my records for the month as a whole are a little understated.  I totalled 156.6mm for the month, amounting to 214% of the median for May.  For the year to end May we are at 633mm which is 176% of median falls to the end of May.  Here is a chart of daily fall, including the adjustments described above (note that there are several days early in the month with a record of 0.2mm which barely show up in the chart):

The progress of my prorata estimate for the year is interesting.  Having had falls well over median every month so far this year it is not surprising the prorata estimate is high.

I have added a section at the end of this report comparing 2025 rainfall at the BoM Airport and Gabo Island sites.

Temperatures

The development of the anomaly (difference to long-term mean) shows a cool first few days followed by a warm spell, sustained to the end of the month.

A chart of daily extremes give a pattern consistent with the above.

A time series of anomaly values resembles the Alps. Using a 12 month moving average to remove seasonal factors shows that the series is rising, but applying a trendline to that series suggests it is dropping.  I think "wait and see" is the best option here!

There were no days with both extremes significantly below long term, and only 1 day with both significantly above.

Minimum temperatures

The average minimum for the month was 10.05C, 0.73C above the average minimum for May recorded on my WS.  The lowest I recorded in the month was 5.3C on the 20th: one of only 3 days significantly below the long term average minimum for May.  The highest minimum temperature was 14.9C on the 23rd: 4 days were significantly above long term.  Overall 22 minima were above average and 9 below.

Comparing with recent years the time series for average monthly minima over financial years shows a continuation of 2024-25 as being warmer that usual.

Maximum temperatures

The average maximum for the month was 19.67C, 1.54C above the average minimum for May recorded on my WS.  The highest I recorded in the month was 27.0C on the 6th: one of 10 days significantly above the long term average maximum for May. 3 days (5th to the 7th) were very significantly above average.  The lowest maximum temperature was 11.7C  on the 18th: 2 days were significantly below long term.  Overall 23 maxima were above average and 8 below.

Comparing with recent years the time series for average monthly maxima over financial years shows a continuation of 2024-25 as being warmer that usual.

Humidity

The records for the month were reasonably normal for such a rainy period.

Wind

See comment in preamble.

Extra: Rain at Airport and Gabo

This section arose from a feeling that rainfall recordings at Gabo were lower than I expected compared to those at the Airport.  For the year to date the 2025 ( to 28 May) falls recorded by BoM at the Airport and Gabo were 682mm and 478 mm respectively.  Comparing the daily falls over 148 days there were: 

• 78 days where both sites reported the same amount (mainly 0mm!)
• On another 54 days the difference was less than 5 mm one way or the other.
• On 13 days the Airport recorded greater than 5mm more than Gabo; and 
• On 3 days Gabo was more than 5mm above the Airport.

Three days stand out where the Airport recorded much more than Gabo which I think gave rise to my feelings of doubt:

• 8 February 42.4 mm vs 4.2mm
• 10 February 73.4 mm vs 10.8 mm
• 24 May 76.2 mm vs 49.4 mm

However I think that looking at the overall series I could not conclude there was any consistent pattern I could raise with BoM.

I did also look at Green Cape (GC) but found that 14 days had missing readings and for another 5 days the falls were cumulated over more than 1 day.  One of the missing data periods, in January, included a significant rain event (27 mm at the Airport, 14 at Gabo).  I also couldn't pick a consistent pattern between GC and either of the others where data was available for all three sites. 

My conclusion was that while the differences were surprising given the 2 sites are quite close (17km in a straight line) with apparently similar exposure and neither site affected by hills (on 8 -10 February the wind at Gabo was from SE, on 24/5 it was from NW but Howe Hill is ~8km away), explaining this was above my pay grade!

May 23 rainfall

 This covers the rainfall even of 23 May 2025.  Although the rain came down the East Coast looking at a BoM map it doesn't look to me like an East Coast Low.  Here is the radar at 1150 hrs on 23 May 

.. and again at 1915hrs.

Over the whole day my Weather Station collected 77.6mm.    Here are some other local sites (neither of the Wunderground sites in Mallacoota of which I am aware are currently online, possibly reflecting the unreliable power supply at present).  I am very surprised at the low fall recorded at Gabo.

My WS shows falls through the day becoming very heavy in the evening.

The low fall at Bombala AWS suggests there will be little water coming down from the headwaters of  the Genoa River, but the worthwhile rain at Nungatta gives warning  of a good flow on the Eastern side of the ranges coming down Nungatta Creek affecting the Genoa Gorge Flood Gauge later on 24th.  At present it is well below Minor Flood level, but rising.

The fall at Nungatta may/probably also indicate rain falling in the headwaters of the mighty Wallagaraugh, to join up with the Genoa at Gipsy Point.  Together these flows  may offer interesting times for Bottom Lake in the near future.

The height peaked at 0745 on 24 May and has been slowly dropping since then.

The evening was blessed with an excellent sunset:

THis was a panoramic shot from my phone.  An idea to experiment with.

As the lightfades.

On the 25th I took a drive up to the (not close to a) flood gauge.  When I arrived it was measuring 1.12m so had dropped 0.27m (pretty close to a foot in old money) from the peak around 0800 hrs the previous day.  All was very calm upstream ...

.. but rather less so downstream.

The curious point was the state of the track from Wangarabell Rd.  Someone seems to have tried pruning some of the vegetation beside the track.  However:

• they seem to have whacked small trees at random (several species, at various distances from the track); 
• used very crude implements not an axe nor clippers or a brush cutter);
• given up after about 300m (ie about halfway to the small shed); and
• just left the material scattered across the track (thus making it more difficult to walk on).

April 2025 Weather Report

 This is starting off as a quick draft, with preparation commencing before the end of the month, focusing on a few core variables (although I have bolted down a few data-burrows in the rainfall area).  The key comments are that by the end of the period it had became a very wet and very warm month overall. Some key numbers are here.

Rainfall

For the 4th month in a row rainfall was well over the median value.  The outcome was the water level in the Inlet rising sufficiently to close Lakeside Drive.  While this is the first time I can recall that happening with the mouth open, a long-term resident has advised that "Lakeside Drive has always flooded in my memory. Closed or open to ocean Lake or not!".

The length of the period of over-median rainfall "felt" longer than usual.  On checking my long time series (including data from the BoM Airport site from May 1984 to March 2019) this seemed to be confirmed, but I am having difficulty in presenting this in a clear and rigorous manner. (The longest run is 10 months of below median falls from April 2019 until January 2020: no wonder the fire went so quickly!) 

The total fall for the month at Angophora Drive is 179.8mm (237% of median April fall at this site). I found the recorded numbers to agree well with the collection in my Nylex plastic gauge. The comparison with records from the BoM Stations at the Airport (154.6mm) and Gabo Island (146.6mm) are interesting in a number of ways.

• It is unusual for both sites to be lower than my WS.  As well as the check offered by my Nylex, other observers' records from Karbeethong and Mirrabooka correlate well with mine.
• It is difficult to compare the BoM daily falls (based on a historically based 0900hrs reset)  with my records based on a midnight reset.  However I have achieved that with some effort.

The unusual period is 22-23 April.  During that time the radar image tended to show a line of small cells heading directly up the Genoa valley between the Airport and Gabo Island.  It seemed as though the hills of the Drummer area and Howe Range were shepherding the weather.

For the year to date I have recorded 475mm (179% of the median fall to end April).  Using the records for the year to date to compile a chart of the development of my prorata estimate of the annual fall shows the continual rain in the area.  This contrasts with the rest of Victoria where anecdotes report significant dry weather, as shown in this BoM map (thanks Rob Clay for drawing it to my attention).

I suspect that the average used here is the mean rainfall rather than the median.  The mean is biased upwards by occasional months with very heavy falls in a small number of years.

The mean rainfall to the end of April is 303 mm compared with a median for the period of 265 mm.  It should also be noted that the BoM data will probably not have registered the heavy local falls described above.  Most importantly the map shows a 12 month average including several months in 2024 with very low rainfall in Mallacoota.

Temperatures

The value for the temperature anomaly in April was +1.47C.  The early part of the month was cool but after 7 April one of - or frequently both - maximum and minimum were above the average value for the date.

This continues recent experience resulting in the 12 month moving average plot of anomaly values turning upwards.  

The chart of daily extremes shows that the key contributor to the strongly positive anomaly is the high minimum temperatures.  Particularly at the end of the month maxima were close to or below the longer term average (as expected given the blanket of cloud).

There were only 2, widely separated, days on which both minimum and maximum were significantly above the average, although 12 days had both values above average (expected value 8). 

Minimum temperatures

The average minimum for the month was 13.50C, just below the highest for the District, at the BoM site at the Airport (13.54C in 2002).  It is clearly the warmest recorded at my WS.

The minimum was above average on 22 days, and significantly above average on 9 days.

Maximum temperatures

The average maximum for April was 22.6 C, well above the average for my WS since 2019.  It is below the maximum at the Airport, adjusted to be comparable with my WS which is estimated as 23.8C in 2016 and 2018.

The maximum was above average on 18 days and significantly above on 8 days.

Humidity

The average humidity at 0900 hrs (86.1%) was the equal highest recorded for an April at my WS.  For the afternoon (1500 hrs) the reading (70.9%) was above average, but below 2 of the 6 earlier years.  The daily values were not remarkable.  

Wind

The average wind run at 66.6 km was well below average.  This possibly reflects the wind coming from Southerly directions (14 of 30 readings at 0900 hrs by the Airport site came between SSW and SE) from which my WS is sheltered.  

Flooding April 2025

 Over the two days 21-22 April 2025 my Weather Station recorded 131.8mm of rain.  This lead the SES to issue a flood warning for the Genoa and Cann Rivers.  For the Genoa this indicated moderate flooding. We noticed indications of this on our morning walk on 23 April beginning with the amount of water in the marsh between Lakeside Drive and Bottom Lake.

A puddle forming on the bend at Fisheries Jetty was a further indicator ...

.. as was the disappearance of some jetties.

The Boardwalk was just clear of the water (although an earlier walker posted to Facebook an image of a small mullet on the deck). 

Another traditional road cutting spot.

This shows the level of the Genoa River at the Gorge, 35+kms upstream.  Obviously there is a fair lag before the drop of level gets down to Lakeside Drive.

I decided that I didn't want to drive up to Wangarabell and slither down the track to the flood gauge but decided to check the situation at Genoa Falls (on Genoa Creek, a few kms West of the village).  It was rather photogenic. 

Charles Darwin was getting ready to make an award, but fortunately this guy is still in the gene pool rather than the more tangible pool below the Falls.

Heading back to the village and as expected the Creek was well over the cow paddocks.  (No sign of the Emu which sometimes comes out of this country.)

Moderate flooding seems a fair summary.

The view downstream from the footbridge.

I had a pleasant chat with a land owner about the current situation (and many other pastoral matters).  On hearing of the flood warning he had driven from Bombala the previous evening and noted that while raining South of Bombala it stopped halfway along Imlay Rd and didn't resume until the Wallagaraugh.  The paddocks along Black Creek had spread pretty widely.  

On returning to Mallacoota (about 1300hrs) the signs indicated that Lakeside Drive was closed due to 'water over the road".  At that time it wasn't fully over at Fisheries Jetty, but when I walked down at about 1600hrs it was well over.

To balance the adjectives, Fisheries Jetty was well under.

Mullet access to the boardwalk was now much easier.

The next low point was also rather damp.