Reluctant monsoon frustrates forecasters

Stable dry keeps moisture at bay

Weather
The forecast for rainfall potential in the coming months is a little more problematical. The Pacific “El Nino” event appears to have faded away for the present but there is now a reasonable chance an “El Nino” re-developing later in 2019, but there is still a degree of uncertainty about that.

The forecast for rainfall potential in the coming months is a little more problematical. The Pacific “El Nino” event appears to have faded away for the present but there is now a reasonable chance an “El Nino” re-developing later in 2019, but there is still a degree of uncertainty about that.

Aa

The reluctant start to the monsoon in the NW of Australia continues to impact on the south-east states as air over the “heat engine” part of the continent (the tropical NW) continues to be hotter than normal due to lower cloud cover.

Aa

The reluctant start to the monsoon in the NW of Australia continues to impact on the south-east states as air over the “heat engine” part of the continent (the tropical NW) continues to be hotter than normal due to lower cloud cover.

Warm sea surface temperatures (SSTs) especially between Australia and New Zealand are another contributing factor to the warmth and humidity, and the semi blocking high pressure over the Tasman, preventing any major Southern Ocean cool changes to come anywhere near the SE of Australia is a third major factor. As a result, the hot summer weather is likely to persist but a gradual decrease in the frequency of heat wave conditions will occur from this week. Above average temperatures will persist at least into autumn and probably beyond but the extremes will be lower.

The forecast for rainfall potential in the coming months is a little more problematical. The Pacific “El Nino” event appears to have faded away for the present but there is now a reasonable chance an “El Nino” re-developing later in 2019, but there is still a degree of uncertainty about that.

Atmospheric indicators, such as the Southern Oscillation Index (SOI) which has dropped to around -2 in January but still well within the neutral range, the strength of the SE trade winds in the western tropical Pacific and the cloudiness in the central tropical Pacific, all indicate a fairly well established neutral pattern.

This set up is likely to encourage occasional rain events but only patchy and variable in nature and interspersed by long periods of stability.  Although the NW monsoon is weak, activity in NE tropical Australia is bringing excessive rains to north Queensland and it is likely to bring increasing potential for moisture to feed down over the eastern states at times, resulting in another encouragement for those occasional events. Putting these factors together, and there are a few signs for optimism but it remains unlikely that there will be sufficient widespread falls in the coming months to overcome the severe deficiencies established over the past year or two.

In the longer  term, looking  towards the  period from  mid autumn to mid winter, (April to July), the  Indian Ocean Dipole (IOD)  becomes  the  indicator to watch. At the  moment, the IOD  is zero and all international models  predict  the IOD will remain  neutral (near zero)  through  autumn  which  doesn’t  help  seasonal  predictions  much, but it  has the potential to change and therefore will be watched  closely from  March onwards.​

- DON WHITE, Weatherwatch

Aa

From the front page

Sponsored by