SOI Returns to Negative Values Dave McRae 21st February 05
The 30-day average of the SOI has returned to negative values after a brief push into positive values (plus 1.2 at the end of January). This was the first time since May of last year that monthly values of the SOI had reached positive values (if only just). As of the 25th February the 30-day average of the SOI has fallen to minus 17.1. As we have stated regularly, for there to be an overall widespread improvement in conditions right across the state, it would help if the SOI went into positive values for a couple of months at least.
After a period when the signal of the MJO (40-day wave) has been very weak and difficult to locate, it regenerated in the western Pacific. So for those looking for some more rain it is now considered unlikely to see a renewed active phase of the MJO over northern Australia before early March. Very warm sea surface temperatures in the central and western Pacific appear to be disrupting the typical MJO progression.
Sea surface temperatures in the Pacific remain in a borderline El Niño. Based on the latest observations and forecasts, it is more likely than not that this borderline El Niño will prevail through to at least April 2005. The changes that occur in sea surface temperature patterns in the central Pacific especially in the coming autumn will be crucial in terms of whether this El Niño event continues to persist throughout the rest of the year.