Fig. 1: Satellite photo of a storm off the East Coast of Australia which produced flash-flooding in Sydney while prior to cold frontal passage across Queensland pre-frontal high wind and record heat fueled bush fires.
Discussion: Early-to-mid week featured more extremes related to unusual climate conditions this time in Queensland, Australia. Queensland fire alert was raised to “catastrophic” for 130+ bush fires. The fires were fueled by record heat (104F), high wind ahead of an approaching cold front and dry vegetation. The cold front extended north and northwest from a potent storm off the East Coast of Australia causing flash flooding in Sydney.
The climate conditions producing this early intense fire are unique. Australians are expecting a widening drought and attendant anomalous summer heat and increased fire risk due to developing El Nino. When El Nino is present intensifying drought is common across much of Australia.
While El Nino is steadily organizing another macro-scale dry climate system has matured known as the positive phase of the Indian Ocean Dipole (+IOD). Ocean waters west and northwest of Australia are cooler than normal lowering the evaporation rates for any storms approaching from the west and adding dry risk to the evolving El Nino (dry) climate.
+IOD and El Nino occurring at the same time is unusual but not unique. The most peculiar aspect of the recent climate pattern across Australia is the unexpected presence of steady passing cold fronts of which high wind and anomalous heat occurs prior to frontal passage and occasionally very heavy rains are triggered where low pressure areas are attached to the cold front.
The unexpected strong early summer cold fronts have been caused by an intense positive phase of the Antarctic oscillation (+AAO) which represents presence of an unusually strong polar vortex over Antarctica. The deep trough over Antarctica is ejecting energetic short wave energy enhancing the southern hemisphere storm track along 40 degrees south latitude (known as the “roaring 40’s”) and some of this energy has been crossing Australia.
Cold fronts caused by the +AAO regime affecting Australia are running into increasingly hot air masses fueled by +IOD and El Nino climate and causing fronts to produce extremes (excessive heat and wind or flooding rains).
The +AAO regime may linger and cause additional unusual high intensity early season bush fires accelerated by high wind and anomalous heat ahead of unusually strong cold fronts for early summer.
Fig. 2: Positive phase of the Indian Ocean Dipole and El Nino normally are an ideal combination to produce widespread drought across Australia.
Fig. 3: A super intense polar vortex has hovered across or near Antarctica during November ejecting short wave energy causing weather extremes across Australia and Argentina.
Fig. 4: An unusually intense positive phase of the Antarctic oscillation identifying presence of a strong polar vortex across Antarctica has been present for about 3 weeks. The 15-day forecast is uncertain as to whether +AAO fades (or not).