After an off-kilter start to summer where our easterly trade-wind belt took extended smoko then failed to return, and the standard Northern Australian Monsoon (NAM) has registered its latest start in recorded history* we are finally looking at some action across the tropics.

The BOM-issued Tropical Cyclone outlook was for an average season with eleven cyclones, with four in the Coral Sea. Under La Niña (or La Niña-tending) conditions an early start to the monsoon and TC season was predicted, although the link between monsoon onset is stronger for El Niño years.

Monsoon onset and low pressure development - which is the basis for cyclones - is normally linked to active phases of the Madden-Julian Oscillation (MJO) moving west to east from the Indian Ocean into the Pacific Ocean. We currently have a moderate/strong phase of the MJO moving over northern Australia which is expected to both signal the official start of the monsoon and potentially spawn single or multiple cyclones.

The BOM's outlook for this coming Sunday showing five areas of low pressure being watched for cyclone development (Note: cross-hatching indicates areas outside Australia's watch zones)

It hasn't been the first active phase of the MJO this season. A strong phase of the MJO in late November/early December bought on the wet season in Indonesia, spawning twin cyclones from low pressures off Sumatra. TC Fengal headed west to bring death and destruction to Sri Lanka and India, while TC Robyn drifted southwards into the Australian Area of Responsibility to become our first named cyclone of the season before washing out near the Cocos Islands after causing lethal flooding and landslides in Indonesia. Monsoonal westerly winds from that event stalled in the Arafura Sea and failed to impact areas to the north of Australia and Coral Sea.

The late-developing La Niña and associated strong trade-wind surges in the tropical Pacific seem to have repelled all previous MJO phases, almost as if the MJO were hitting an impenetrable wall.

Why the late onset? There are no firm answers, only tentative hypotheses. Chief among them a changing climate which is reducing confidence in the timing and amplitude of seasonal norms. Our surf seasons have been affected by these reductions or reversals in typical weather patterns. Tropical low pressure in October for example, a feature of the last several years. Despite an El Niño pattern last year and predictions of lower cyclone frequency and intensity and later onset we saw Category 5 TC Lola develop in October - the earliest Cat 5 storm ever recorded in the South Pacific.

Seasonal predictions may become of diminishing utility as we move further into a new period of changing climate.

One prediction climate scientists have made has so far held true. Overall number of cyclones in the South Pacific, including the Coral Sea has decreased in line with climate predictions.

This increasing seasonal variability and overall trend of fewer cyclones may spell the end of the mythical Christmas cyclone swell, relegated to the stories told by red-blotched faces around the front bar.

First Point Noosa unwrapping itself during a cyclone swell (Craig Brokensha)

Back to the present. A flurry of activity is expected as the wave of tropical instability caused by the MJO pushes across the top end and into the Coral Sea.

The Joint Typhoon Warning Centre is interested in a low due north of Cairns with a high probability for cyclogenesis in the next 24hrs. If this beats a low in the Gulf of Carpenteria to the punch it would be named TC Taliah. Potential also exists for TC's Vince and Zelia to follow. With the current instability along the trough line, confidence remains very low over specific outcomes so don't get too frothed up or disappointed over single model runs - we will see a lot of to and fro through this week and into the weekend.

Of more importance will be the broad easterly windfield supporting the developing low pressure centres which should at a minimum set up a long-lasting drumbeat of pulsey easterly swells.

Keep tabs on the actual surf potential from this set-up in the Northern NSW and Queensland Forecaster Notes over the following days, and also in the comments below the line.

//STEVE SHEARER

*Over 70 years since records began.