One of the things we start to look for eqrly in are patterns in the weather that will give clues to the rest of the dry season. To figure out the rate at which high pressure systems are moving through helps to determine when cold snaps and rain will eventuate.
The Southern Oscillation Index can help here as it measures the low pressure difference between Tahiti and Darwin. When it dips that tends to coincide with a high pressure.
However in recent months we have seen a blocking low, where either a low develops off the coast of NSW or moves SW from New Caledonia and prevents the high from moving into the Tasman and sending North the trade winds that bring cool air, and when the cool meets warm near the FNQ coast it generates rain.
Based on the current SOI which coming out of the wet season only shows one clear half cycle, the number of days between the last trough to the peak is 9 days including the trough and peak day. That assumes the cycle will be as clear cut as this current one. So Tuesday 9th will be the coldest day for this full cycle. However we need a few more cycles so possibly the 18th May will be another key day.
The current high is starting to push cool air up and the low will combine to push it up with stronger winds but it will be short lived as the low moves SE and the high is blocked and the air between becomes still, producing foggy conditions for NSW and SEQ.
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