Climate Update - May

TEMPERATURES


With the onshore winds and persistent showers to kick off May over the east coast, this will likely contribute to below average temperatures for May as a whole. The same can be said for far southwest WA, where frontal activity and onshore winds will drive clouds and showers through the region.


The rest of the country looks to be average to above average in terms of temperatures for May.


With the persistence of easterly winds over eastern Australia and a potential blocking pattern setting up in the Tasman Sea, this will prevent any dry cold southwesterly blast moving through southern and eastern Australia until the second week of May at the earliest.





That means that the tropics will remain hot and humid as the build down continues with the monsoonal weather lifting out and away to the equator.


The next week to 10 days will remain warm to hot over the west and north and cooler in the east.


May we see the warmth remain over the north of the nation, cooler in the east with those onshore winds and cloudy rainy weather - and potentially a cooler trend for the back half of the month for the southern coastline with the increase of frontal weather.


With a trend to a more mobile pattern across southern Australia and the northward advancement of the long wave troughs, colder snaps will begin to feature, but after a warm start to May, it is likely overall, that the month will average out as normal.


May is a month that can be notoriously quite stable and steady with blocking patterns. But I do think we will see a more mobile pattern develop as we get towards the end of the first week of May which might start to bring a bigger pattern flip so the forecast could continue to evolve.


Forecast for May


RAINFALL


Signals have shifted during the past week regarding the weather expected through Australia during May.


A blocking pattern early in the month will see a prolonged period of easterly winds over much of eastern Australia, with high pressure anchored over the Tasman Sea.


Rainfall for the next 6 weeks - Euro


A tropical disturbance to the north of the high will likely move west towards the QLD/NSW coasts bringing widespread showers/rain from early in the month with the potential of some heavy falls about.


That moisture may be drawn in over the GDR into the eastern inland, producing some chance of rainfall through early May, but not widespread heavy falls expected.


For the southern coastline, it should be a dry start to the month with the blocking pattern shunting systems to the south and keeping dry air over much of the interior in place.


From the about the 7-10th of May, there is the likelihood of a pattern flip over the south and east, with the blocking pattern breaking down and the chance for a more mobile weather pattern.


A long wave trough below on the 8th could bring a pattern shift? We shall see.

Yesterday however, the model had the long wave parked way out west over WA, rather than over the east, so something is stirring, but it will become clearer on the blocking pattern breaking down in the coming week. So stay tuned.


This will see rainfall chances increase over the southern and western parts of the country from this point. But because the signal is not overly potent, I am keeping the chances of it being wetter than normal at 50%.

SW WA could have an active fortnight period and again towards the end of the month (that was also a signal present last week).


You can see the signals picking up in the early part of May with some members from the Euro model for Perth suggest 50mm is possible, the mean, the green line, has about 25mm which would be welcome.


The tropics could see some residual shower and thunderstorm activity early in the month but that should be gone by the 15th of May.


Darwin won't see that deeper dry air for the next 15 days but the showers may ease, so that suggests that the blocking pattern will be in place over the east, snuffing the cold fronts too the south for a while, though southwest WA could start to be impacted by the first batch of the season.




Interior parts of the nation largely dry however I do note that some modelling wants to bring in cloud bands across the country - which I am not drawing in here as the signal is not strong enough.


The dry air (brown tones) means not much rainfall expected for a while into May for the inland but the warmer tones on the east coast show a significant amount of rainfall is possible to kick off May in that configuration. The short term forecasts will refine this weekend.





Overall the shift to a wetter signal in the east is due to the likelihood of easterly winds, especially early in the month, bringing a wet start to May.


The wet signal in SW WA is connected to an active period of frontal weather, especially if a secondary blocking pattern develops in the east during May allowing the long wave trough to dominate the region.


Image - Climate Update - May Rainfall





% chance of exceeding median rainfall for May.


Just because you may be shaded in a 60% chance of exceeding the rainfall - remember there is a 40% chance you may not!


This forecast will be updated again with a 2 week outlook next Tuesday 27th of April.



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