MODELS AND ALL THINGS RAINFALL - THE WET SIGNAL IS UNDERWAY AND SET TO BUILD THROUGH THIS WEEK.

The charts will continue to chop and change as advertised as the modelling continues to get a handle of the tropical weather up north and they adjust to factor in perhaps a protracted period of positive SAM conditions over the Southern Ocean.


The models are in reasonably good agreement on the wetter weather still being over northern and eastern Australia. There is evidence however that the rainfall could be introduced into eastern SA and perhaps southern WA as a middle level trough begins to move into the region from next week bringing the showers and thunderstorms into the forecast.


So there are still some moving pieces to iron out, especially over the tropical north with the tropical cyclone placements.


A REMINDER

Models and the Tropical Lows

The model split on the tropical low formation and then the movement of these potential lows is clear when you present it like this with the three major weather agencies that there is significant divergence. These are the paths that are being identified by the models and not all three agencies agree on one low so we need more time through the week to watch the data sets closely together. But each of these pose interesting outcomes in terms of spreading rainfall through the nation.

Tropical Depression Risk - This Week

With the monsoonal flow developing over the open water during this week you will notice larger clusters of thunderstorm activity. These clusters may become more organised and low pressure systems may develop. Given the elevated SSTs through the region (not as elevated as per January but it is sufficient) depression formation is quite likely from later this week and through the weekend. Refer to the chart to that shows you where the models are placing the tropical depressions and where they ago. The confidence in identifying the system that is the dominant tropical low is very poor.

Tropical Cyclone Risk - This Week

With the monsoonal trough sitting over the open water and the MJO passing through the north of the nation from the weekend and into next week, any tropical low that forms in the waters offshore the coast, carry a moderate chance of developing into a cyclone. The most likely outcome based of analogue data is that a system will form north of the NT and then head west through the Arafura, Timor and then Indian Ocean. That will then deepen offshore northwest WA and then turn towards the Pilbara and then inland through WA. That would spread heavy rainfall over the northern tropics but then pull the heavy rainfall shield away from the NT and over WA and another pulse of monsoonal weather would develop over Cape York.

MECHANICS

A fairly simple graphic overview of the mechanics in play to produce more rainfall across the country. For the east, it is watching the upper level low/trough over the eastern inland and how strong that feature is as it moves closer to the east coast where the onshore winds meet the unstable air to produce showers and storms inland and more frequent heavier showers along the coast. The monsoon trough up north will begin to influence rainfall chances over the eastern inland from next week.

Flood Risk Forecast - Next 2 Weeks

Flooding over northern and eastern areas of the nation remain a moderate chance, tending high near the coast with a low risk extending inland. The low chance is being drawn in over much of NSW and QLD and extending into northeast and eastern VIC. I am leaving the rest of the nation out of the risk for now with no clear guide on the tropical systems impact on the country. However a tropical system moving west away from the NT through WA and into the western interior is possible but not highly probable at this time, but an event like that could bring flooding risks back to the charts over western and central parts of the nation so for now just a be on watch situation for these areas. State based charts may be issued tomorrow or Wednesday.

Lets take a look at the latest data


SHORT TERM

Short term model analysis from yesterday is unchanged as we track the a wet signal across much of the nation with the positive SAM and MJO rotating through the north over the next week or so. This will lead to deeper moisture and heavier rainfall chances for the east and north of the nation and some evidence the rainfall may enter parts of SA and WA through next week.


UKMET - Rainfall Next 7 Days - MODERATE CHANCE

Not much change from yesterday, really showing the trough over the north and the eastern inland. Otherwise the rest of the nation quiet. Positive SAM setting up a wet period for the east. Watching the upper trough south of WA and SA next week, look to longer term models to see impacts further east.

ICON - Rainfall Next 8 Days - MODERATE CHANCE

Like the UKMet, showing significant rainfall and moisture over the north and east with heavy falls developing in the onshore flow in the east and along the north coast of the NT and QLD with the developing monsoonal flow. Keeping an eye on the upper trough over southern WA and SA next week, that may surprise.

MEDIUM TERM

The medium term offers widespread rainfall ongoing for northern Australia with the MJO and the positive SAM phase may persist into the medium term, the members associated in forecasting the SAM have now swung back to keeping the positive phase in place into the medium term before it eases. This would support little change to the overall rainfall distribution. If the SAM turns back neutral then this may open the door for more substantial rainfall to resume over the southern and southwestern areas of the nation, if not, the chance of rainfall should increase. The MJO remains in the phase 4-5 range and keeps the wet weather going over the NT and QLD in particular.


CMC - Rainfall Next 10 Days - MODERATE CHANCE

Has heavier rainfall over the eastern states and extends the heavier rainfall further west than the shorter term models. I am leaning towards pushing the rainfall chances into SA in the coming forecasts with the agreement starting to improve on that idea. Rainfall comes into WA as a mid level trough deepens next week bringing up falls for southern Ag areas. Flooding a risk for eastern and northern inland areas of the nation so that will need to be monitored.

EURO - Rainfall Next 10 Days - HIGH CHANCE

Has the monsoonal flow deepening through the week with heavy rainfall coming in next week rather than this week. Heavier rainfall through this week over the eastern parts of the country and persists into next week. The rainfall chances coming up for southern parts of the nation back towards southern WA with another trough.

ACCESS - Rainfall Next 10 Days - LOW CHANCE

Exceptionally heavy rainfall for the east of the nation with a stalled trough and sharp upper cold pool feeding off the deep easterly flow to produce extensive above average rainfall. Not overly convinced on this forecast but it is plausible and will come down to whether we see tropical entities drawn into the unstable flow over the east to produce this. Can see two tropical systems on the board, one out west and one moving over north QLD and then taking a tour of the QLD and NSW coast.

KMA - Rainfall Next 12 Days - LOW CHANCE

Showing very wet conditions for the east in the onshore flow and extends that back towards the SA/NSW border. Widespread rainfall developing over the north with the monsoonal flow building north of the nation. Otherwise the interior mostly dry but falls should start to return to southern and western areas of the nation as we track tropical mischief through the Indian Ocean.

GFS - Rainfall Next 16 Days - MODERATE CHANCE

Very wet for the eastern inland for the coming week and this then extends over southern areas of the nation too as troughs emerge from southern WA and then over SA before running into the deep moisture left through the eastern parts of the nation. This would be bring flood chances up for some parts of the nation's eastern interior. Northern areas watching a tropical low in the short term that could spin up some heavy rainfall later this week into the weekend for the NT and then more broadly the tropics next week with the trough. That moisture then moving into central and northern QLD with a flood risk.



ENSEMBLE DATA

They are in good agreement in terms of the placement of the heavier rainfall and spread of the rain through the country. The differences you will see is in the single data runs that many of you have via the myriad of apps (which tells you the same thing) so you will see your rainfall numbers bounce all over the place as a result.


GFS - Rainfall Next 16 Days (median of 35 members) - HIGH CHANCE

A high rating based off the heavier rainfall potential for northern Australia. I want that to be a focus of the forecasts moving forward. The engine room for some upper end rainfall for parts of northern and eastern Australia.

CMC - Rainfall Next 15 Days (median of 30 members) - MODERATE CHANCE

EURO - Rainfall Next 15 Days (median of 51 members) - MODERATE CHANCE



LONG TERM

The wetter signal continues for the east and north with the wet seasons in both regions continuing and the rainfall set to return to WA and SA once we get a neutral SAM and the ability for more frontal weather to resume south of the nation, helping to pull moisture down from the north and then swinging it through the country from northwest to southeast.


GFS - Rainfall Next 5 Weeks - MODERATE CHANCE

Wet signal builds on the longer term GFS.

CFS - Rainfall Next 6 Weeks - MODERATE CHANCE

That wet signal is not going anywhere on the longer term modelling. More tomorrow on that.



More coming up from 8am EDT.