THE absence of north-western winds in October meant that increasingly hot air forming over the north-west of the continent did not have the mechanisms to move into the south-eastern states, or at least the coastal parts of NSW and Victoria.
Absence of cloud – partially as a result of cooler waters in the north-eastern tropical Indian Ocean, has meant that hot air has continued to build over the “heat engine” areas of northern and north-west Australia and above average temperatures will return to all of NSW and adjacent states during November.
Warmer than normal temperatures are favoured to persist through the summer months, but with lower than average wind speeds, evaporation levels are only expected to be fractionally above normal.
The long-term indicators have only marginally changed in the last week or so.
There is still pretty good chance that at least weak El Nino is developing in the Pacific although its progress is a little “stop-start” and more evident in the ocean temperature patterns than in the atmosphere.
For example, the 30-day running mean of the Southern Oscillation Index (SOI) which was about -8 in September and -7 in August, both marginally in the El Nino range, has climbed back to +2 in October which is in the middle of the neutral range, giving an indications that the atmospheric structure is holding off on heading towards an El Nino .
This encourages the prognosis of only a weak and short lived El Nino event, if, indeed, it does develop at all. (There is still a slightly better than 60 per cent chance it will).
Severe storm activity is often more prevalent in these weak but developing situations, but this is more likely over Queensland and north-eastern NSW.
Such activity can also locally boost rainfall but overall, apart from a one off event or two, there will be extended periods of stable weather in the coming months.
The chances are a neutral pattern will return in 2019 so rainfall amounts are likely to be closer to normal from autumn on in many parts of south-eastern Australia.