MEDIUM TERM FORECAST - DRY FOR A WHILE BUT THERE ARE HINTS OF THE PATTERN TURNING UNSETTLED.

It is an easy forecast this week, a fine forecast for much of the inland of the nation, just the odd front passing through the southeast, mainly impacting Tasmania with moisture passing from SWLD of WA through the Bight into Tasmania with scattered showers/rain about. Inland areas, under the stable dry airmass will see plenty of sunshine.


Now from next week, once we see the high pressure system move along, the weather will start to shift warmer, however the bigger impact will be the moisture being drawn in from northern parts of Australia through to the south and southeast.


There are systems starting to emerge on the charts in the medium term, GFS a little earlier in it's recent run, but the Euro also has some sign of unsettled weather developing next week.


Lets take a look


THE FORECAST CHARTS

Rainfall This Week - September 6-13th 2021

A dry week under high pressure with the rainfall expected to remain fairly coastal and inland areas dry. It is a stock standard break week after a major weather event as the atmosphere responds and recovers.

Rainfall Next Week - September 14-21 2021

Increasing signals for moisture to increase and inland troughs to form, resulting in a broad area of light rainfall coverage throughout the nation, this will refine as we get better clarity. But bookmark that this will be the period where we see some showers developing over inland areas with the possibility of thunderstorms. Northern areas will see an increase in moisture which is where the source of rainfall chances will be derived from as well as the easterly winds, the Positive SAM may be influencing rainfall opportunities during this period over the eastern inland.

Rainfall Anomalies - Next 2 weeks.

This is showing a drier bias over the east, marginal bias, related to this week of no rainfall as the weather is dominated by high pressure. But you will find that the brown shadings will shift as better clarity is derived for the following week rainfall which will extend through NT and SA and points east at this time. The west will turn drier after this weeks rainfall. Good chance of above average rainfall for the northern tropics with increased falls with trade winds freshening and the return of early season showers and thunderstorms. Some areas have already seen above average rainfall through the brown shading area over NSW and VIC and above average rainfall through the outback and NT.

Temperature Anomalies this week - September 6-13 2021.

The colder air that was forecast to come through as a second impulse today, is over the Tasman Sea, so temperatures have been allowed to recover quicker, though still below average today and tomorrow for much of the eastern and central inland. The nights below average too leading to frost. Later this week, the warmer than average weather returns as much of the nation sits on the northern flank of a long wave passing over Tasmania. The heat levels come down over the north with drier air but the above average temperatures continue.

Temperature Anomalies next week - September 14-21 2021.

The warmer weather from this coming weekend will continue into next week, though with increasing moisture and the threat of rainfall returning with persistent troughs, I am leaning to temperatures falling away later through this period with increasing rainfall chances over southeast and eastern Australia. The warmer and much more humid weather is expected to continue over the northern tropics.

Moisture Watch Week 1 - September 6-13th 2021

The moisture is limited (yellow zones) with the high pressure system taking full control and drier air in the wake of the large scale event over the weekend, keeping the nation generally cloud free with warmer weather developing. Moisture in a narrow band from the Indian Ocean will pass through SW WA and into the southeast o the nation will bring areas of rain and showers. The trade winds brings back showers to FNQ but the showers and storms redevelop from the weekend at this time.

Moisture Watch Week 2 - September 14-21st 2021

The moisture is increasing in the medium term throughout the eastern and central parts of the nation once again, very similar to the spread from last event with the moisture being drawn in over the nation from easterly winds, which then gets propelled west and turned south and southeast with troughs approaching from the west. There is little influence from the IOD at this time, with moisture being pushed away from the nation in broad easterly winds over the eastern Indian Ocean.

DATA SETS

GFS 18Z - Surface Pressure Pattern for the next 2 weeks

Clearly a quiet week this week with high pressure but it is next week when we see the charts turn more spring like with troughs of low pressure beginning to develop over the nation - now pinning these down with any specificity is impossible, but the weather is likely to turn unsettled through the second half of the outlook, so just bookmark this for planning and we can track it together this week.

GFS 18Z - Precipitable Water Anomalies for the next 2 weeks

The anomalies paint the picture where the weather is dominated by dry air this week which was well forecast last week, then the moisture does return from the north and the east with onshore winds and the positive SAM phase that has some merit in developing, introducing that humid air over northern and eastern Australia. It is now a matter of troughs over the southern and western parts of the nation and whether they are in phase with the moisture to produce showers and storms.

GFS 18Z - Rainfall for the next 2 weeks

Rainfall increasing in the second half of the outlook and clearly connected to moisture being lifted by troughs and low pressure as they develop later this weekend into early next week onwards.

INDIAN OCEAN INFLUENCE - NEXT 2 WEEKS

Euro - Simulated Infrared Satellite - Next 10 days

This product shows how suppressed the Basin is nearby WA and with conditions remaining fairly inactive for a while south of Java, this will mean for rainfall chances we will be relying on the easterly winds over Australia being drawn west through the nation before troughs pick up that moisture leading to rain breaking out.

Euro 12z - Precipitable Water Values - Short Term

This paints the picture of the moisture over the basin being drawn southeast into the frontal weather diving south over WA, with areas of rain, then that moisture passing south of the nation into the weekend. Note the moisture over the basin is well west of the mainland and somewhat below average in pockets, meaning that less influence is likely from the IOD during the next 2 weeks.

GFS 18z - Precipitable Water Values - Medium Term

Similar to Euro - the influence from the IOD is remaining quite low at this time with moisture still remaining below average for parts of the basin meaning that little impact and influence will be had from this driver at this time which is cause for some concern - as mentioned I am not satisfied on current observed weather from this region, that we will see anything from it over the coming 2 weeks, but this can change rapidly so keep up to date here.

GFS 18Z- Precipitable Water Anomalies - Medium Term

We want to see more green and blue shadings, basically across the basin, to see rainfall chances increase over the coming week or so.

THE DRIVER TO WATCH THIS FORTNIGHT.

The SAM is the driver that will be key to how much rainfall develops over inland areas and where. If the phase deviates into a positive phase more readily, then we will likely see these troughs and showers and thunderstorm events break out over Central and Eastern Australia as well as an increase over northern tropics as well with increased humidity. It will also see the westerly wind belt take a trip further south. This is key to seeing more elevated rainfall chances over inland areas, with a lack of dry air being transported inland behind the fast flow pattern.

I will have a look at the next 6 weeks tomorrow as I am still of the belief things will start to shift and for some areas, the tap may be turned back on big time, but pinning down when and where that happens remains up in the air - we are starting to see signals across all models, now we have to be patient to see if it becomes reality.

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