2019 Spring Discussion Thread (Southern Hemisphere)

Quoted from Canterbury Snow and Weather Watch (NZ):

Summary of the 9th September 2019:

Perth: 33.1C/8.3C

Jandakot: 32.2C/7.3C

Light winds shifting N/NE 20-30km/h in the morning turning W 10-20km/h in the late afternoon shifting S 15-25km/h in the late evening.

2nd hottest September day ever at Perth Metro (and most likely Jandakot too ). Other notable maximums in the region were: Swanbourne 32.9C, Albany: 29.2C. York had diurnals of 30.1/2.1 so 28C of diurnals!! Collie had 29.5/2.1 so very impressive too

Another vigorous round of ECL incoming! This time, focused chiefly on the Mid-North Coast:

Nice looking cold front in SA

Just got back from visiting family in NZ. Terrible weather - unseasonably cool for mid-spring. Mostly overcast and drizzling with strong E, S or SW winds. Christchurch had a few nice days though:

Bit of Analysis on the spring/summer heatwave volatility for 2019-20, concering the above average temperatures in the Pilbara.


Fig. 1



Source of Heat:
The source of the common spring and summer heatwave for the SW corner of Western Australia is the alignment of high pressure in the pilbara which pulses heat down the coast as high pressure moves to the Great Australian Bight. This "heat-drag" is fuelled by a low trough that commonly rings the top half of the country as seen in Fig.1. This pattern, combined with a cold front that pushes the air eastwards to South Australia and Victoria creates the short, sharp heatwaves of spring that have been beginning to take place in the Spring so far.

Figs. 2 and 3





The Anomaly:
Evidence of record-early and near record-strong pattern can be seen in the record highs for each month near the coast, the average highs in the Pilbara (where the heat is sourced) and average highs further east in the goldfields (where temperatures are sustained for longer).

1) Record to near-record heatwaves in Western Australia:

The first major event was the record heatwave of August 27-28 where stations from Carnarvon Airport to Cape Leeuwin (recording for 114 years) broke their August and winter records. 19 stations broke their August record and 16 their Winter records. Whilst 2 tied their August records (one being Kalumburu which wasn't in the path of this heatwave) and 2 tied their Winter records. As seen in the average max and min maps (figs. 2 and 3), temperatures were around average all over the state with higher diurnals in the far eastern interior but a significant warm patch in the Pilbara, the source of the August heatwave. 

The second statistic to show this heatwave intensity was the amount of warmth in August; the month ended around 0.5C above average with below average minima bringing it down due to very sunny skies. Yet there was a surprisingly high amount of days above 24.5C (4 days, 2 days above 25C); this can be compared to the very warm August 2014 which only record 3 days above 24.5C and 2 above 25C despite averaging maxima 1.4C above Perth Metro of 2019 (21.6 vs 20.2). A very similar August (sunny, average rainfall, very similar max and min) of 2011, only recorded 2 days above 24.5C and 1 above 25C.


Fig.4 



2) September: continuing heat spikes

September continued with heatwaves between the 8-10, 23-24 and 29 of September all recording in the high 20s to low 30s. 33.1C at Perth Metro on the 9th was also the 2nd highest September maximum on record and would have been tied as the earliest 30C day (with Sep 9 2015) if it weren't for the record breaking August 28. Also noted were 10 stations in the South-west or goldfields districts that boasted record September maximums and a further 4 tied those records. A ridiculously high 45 stations broke their average September maximum record, with one tying it; this shows how record breaking it was, with 45 surpassing the record and only 1 tying! What also has to be said is that 5 stations broke their record September minimum (although one was in the Kimberley and will be ignored) which can be attributed to high pressure pooling in the east of the state after a cold front, these records were all between 6-8 September. The interesting factor was that most of the Pilbara was slightly above average. Looking at fig. 4 and ( www.bom.gov.au/cgi-bin/charts/charts.browse.pl ) which is a loop, you can see the dominance of the high pressure systems from 7-16 Sep and 23-30. This shows that the month; although exhibiting the still unusually strong heatwaves; had a more moderated pattern with the stronger and longer-lasting high pressure.

Fig 5. 

3) October: a return to the extremes

October saw a return to fairly average temperatures on the coast but far above average in the Goldfields and Pilbara (3-4C above in the Pilbara and 5-6C above in the Goldfields) as the strength of heatwaves generated by the Pilbara was inclined in a direction towards the goldfields rather than the SW coast. This resulted in the Perth region receiving plateaus of average-slightly below average temperatures spliced by heatwaves on 8-9, 19 and the 26-27. Although there were still 3 days above 30C recorded in Perth, compared to the average of 2.3. And Perth airport, further away from the seabreeze recorded 4 days of 30C+ (with one 29.9C day) compared to its average of 1.9!
Pilbara locations had anomalies of: Karratha: +3.6C maxes, +1.6C mins; Port Hedland: +4.2C maxes, +1.9C mins and for the generation of heat, Telfer: +3.5C maxes, +3.5C mins. In the real affected areas of the Pilbara heat-pump; anomalies in major centres were: Kalgoorlie: +3.9C maxes, +2.7C mins; Southern Cross: +2.2C maxes, +2.1C mins. Also seen is the change of location of record-breaking heat, with October mean max temperatures broken at 7 locations in the Pilbara, Interior and Goldfields and 3 being tied in the same districts. Record maximums for October were also observed at 3 locations between the 10-11 October in the Pilbara and Goldfields, with 2 other locations (one near Perth and one in the Goldfields) tying their previous October record maximums. 

Conclusions:
With the evidence of initial pumping of heat from the pilbara, movement (and precendence of this the past spring) of the heat via strong high pressure and troughs town the WA coast; then the further movement into the Goldfields. It can be assumed that the heatwaves, if positive anomalies continue in the Pilbara over the coming weeks; will only intensify and record maximums could be observed for both November and December in areas of South-West Westrn Australia and the Goldfields region. This Anomaly can be observed by my previous points and seen in data over the past few months; with temperatures staying 1-3C above average for the next week and looking likely to stay above average with no reason to change (no early summer storms); it is looking more and more likely that at the very least Western Australia will see the development of very powerful heatwaves and heatspikes in the near future. 


A reference to the divisions of western australia in an easily readable map.



Sources: 
October stats: www.bom.gov.au/climate/current/month/wa/summary.shtml
September : www.bom.gov.au/climate/current/month/wa/archive/201909.summary.shtml
August: www.bom.gov.au/climate/current/month/wa/archive/201908.summary.shtml

I may add some more later.

That must be 2007BC

This thread's name is the biggest eye sore I've seen lately. Do I have permission to change it to 2019 Spring Discussion Thread (Southern Hemisphere)?

How about next time, we merge the NH and SH seasonal threads together, akin to the photography threads?

There is an extreme NH member>SH member disparity here, so might as well.