NATIONAL WEATHER PICTURE - PM EDITION - FRIDAY MAY 28TH 2021

Headlines


  • A blast of bitterly cold southerly winds churning up the Tasman Sea this afternoon.

  • Another storm event developing over WA today and into the weekend.

  • Settled skies after widespread frosts over much of the east.

  • Drier air is coming to northern Australia.

A significant push of cold Antarctic air has enveloped the Tasman Sea this afternoon with widespread showers, storms and potentially a lot of hail, sleet and possible snow working it's way towards NZ. On the western flank of that, a fast moving trough is riding up the NSW coast with gale force winds and seas rapidly rising. Severe weather warnings are in place for that event.


Out west, another pulse of showers and thunderstorms has developed along a trough and front sitting offshore. Some widespread rainfall has been observed between Exmouth and Kalbarri today with thunderstorms in the mix. Scattered thunderstorms have also developed near Perth and heading into the Scarp and out towards the Wheatbelt this evening. A taste of things to come.


In the south and east, we have got high pressure that is strengthening over Bight waters, contributing to the high amplitude pattern that is underway over much of the region. Under the sinking air, the cold air that was worked north overnight and this morning from that vigorous southerly is trapped over NSW leading to high chances of frost this weekend, that peaks in multiple states on Sunday morning.


The colder air will be a blessing for those living in the tropics, hanging out for those lazy hazy dry season days. A drier southeasterly surge should arrive around Sunday night or Monday. Cooler nights are coming.


National Satellite Picture - Valid 2pm EST.

High cloud streaming from the developing rain event across WA into SA, is mainly fair weather, torn apart by the upper winds but also the dry stable air that is place, with sinking air motion also decreasing the cloud coverage. Over the Tasman Sea, we can see a large surge of southerly winds bringing in very cold air into NZ this afternoon and for the weekend, large seas and damaging surf for the east coast. Out west, thunderstorms have broken out in unstable air ahead of a trough and cold front set to bring heavy rainfall this weekend. Low cloud over the southeast is producing light showers about parts of the coast.

Satellite Imagery of the Tasman Sea shows the impressive surge of southerly winds connected to that developing low pressure system west of NZ this afternoon and evening. Severe weather is likely to impact the NSW coast along with gale force winds. Conditions likely to ease from early next week as the pattern settles down.

The forecast wave heights for the Tasman Sea as displayed in recent days have not deviated much from the 6-8m forecasts with freak waves to 10-12m in region. Dangerous currents, coastal flooding and erosion likely as this event coincides with the moon cycle which is now waning from the super moon earlier in the week.


Forecast Wave heights for the weekend - Valid Friday May 28th 2021.

Out west thunderstorms have developed along a trough sitting offshore, with some moderate falls occurring between Exmouth and Kalbarri today. The rainfall and thunderstorm coverage will increase overnight and through the weekend as a low pressure system develops over the SWLD.


Thunderstorm Forecast for Friday 28th May 2021.

90% chance of thunderstorms developing within the pink zones within 20km of a given point during Friday. The risk tapers down 10% per colour down the wheel.

Current thunderstorm analysis at lunchtime shows moisture (green) sitting off the NW coast which is likely to be pulled onshore by the coldfront (blue) moving east over the coming day or so. The trough and unstable air in the red zone should start to promote showers and thunderstorms which have erupted this morning (yellow) off the coast, but now starting to move onshore. More of this thunderstorm activity will develop along the coast and move inland over the coming 12-24hrs.


Weather Matters storm analysis - Valid 12pm WST Friday 28th May 2021.

Temperatures today have been relatively cold in the southeast where clouds and drizzle, some snow as well over elevated parts of SE NSW and NE VIC has been observed. The cloud breaks up as you move north and west of the divide into NSW and QLD. Windy about the coastal fringe with high wind chill. Seasonal conditions elsewhere, though still gloomy over the southeast which is making it feel cooler than advertised. Warmer than normal weather for the north will start to change through the weekend and next week with that drier surge coming in from the southeast. A mild over the west ahead of that change sweeping through over the weekend, with cold days under the low over the south coast Sunday onwards.


Temperatures as of 230pm EST - Friday 28th May 2021.

That cold wedge of air over the southeast of NSW and eastern VIC will continue to be in place into Saturday before some brighter skies develop on Sunday. Severe frosts are likely as the wind goes calm Sunday morning and Monday morning. But away from there it is feeling pretty good and near seasonal.


Temperatures as of 230pm EST for SE Australia. Valid Friday May 28th 2021.

Rainfall for the next 10 days is looking promising if you are living out west with a severe weather event likely to unfold this weekend with a very productive rain bearing low slowly moving through. Out east coastal showers about the NSW coast will be more frequent about the Hunter and lower Mid North Coast this weekend. Showers clearing the southeast over the weekend. Then next week, all eyes will be on the north and the west of the nation to see how the remnant low behaves and whether it can cut off and run into moisture that will be riding the jet stream over northern Australia.


GFS 00z run - Rainfall for the next 10 days - Valid Friday May 28th 2021.



Rainfall for the next 10 days - Valid Friday May 28th 2021.

No changes from this morning's cycle with still no strong signal for rainfall over the east, the area indicated is broad and will remain so until better data comes in later in the weekend. Rainfall out west could cause some flooding issues about the south coast after a wet May, and for adjacent inland areas who are running above average. Elsewhere, light falls expected over the coming 10 days. That area of no rain over WA could fill in if the low pressure over southern WA moves further north than east early next week.

Synoptic Scale Discussion


GFS 00z run - 500mb/18000ft flow pattern - Valid Friday 28th May 2021. Saturday.

A large low pressure system in the Tasman Sea will continue to race north before turning towards the east during Saturday bringing damaging to destructive surf and gale force winds to the east coast with some showery periods. An big upper ridge over the Great Australian Bight is controlling the majority of southern and eastern Australia's weather with the inland set to see sunny and cold to cool conditions after morning frost. Out west, an upper low approaches with a front driving rain and thunderstorms along the west coast extending inland. Some heavy falls are possible.

GFS 00z run - 500mb/18000ft flow pattern - Valid Friday 28th May 2021. Sunday

The large low in the Tasman Sea begins to lift out and turn to the east over NZ on Sunday with severe weather over the North Island and severe weather for the NSW coast beginning to moderate, as winds drop below gale force. High pressure controlling the majority of the mainland with severe frosts possible in the morning on Sunday over a wide area with sunshine to follow and light winds. Out west, the upper low begins to broaden and deepen with widespread showers and thunderstorms, areas of rain developing along the south coast, especially between Margaret River and Albany with heavy falls. Cooler air from the southeast racing through QLD to the NT border.

GFS 00z run - Surface Pressure Pattern and Rainfall - Valid Friday 28th May 2021. Sunday

Rain and thunderstorms moving onto the west coast with that trough and cold front which will deepen into an upper low offshore with a surface low forming underneath that to the southwest of Perth. Fine and dry elsewhere away from coastal NSW where squally showers will be in progress.

GFS 00z run - 500mb/18000ft flow pattern - Valid Friday 28th May 2021. Monday

The low in the Tasman has moved off now allowing the ridge to move over the southeast promoting calmer conditions, though waves will still be powerful. Over southeast Australia warmer days after another cold start with winds veering into the northeast. In the west, a slow moving low near Albany is creating areas of rain, locally heavy with gusty winds along the south coast. Widespread showers, hail and thunderstorms for the remainder of the SWLD though the central areas and up to the Pilbara should turn dry.

GFS 00z run - Surface Pressure Pattern and Rainfall - Valid Friday 28th May 2021. Monday

Rain and storms progressing east through inland WA with that extending back to the northwest over the Pilbara and Gascoyne. An upper low over the SWLD with a surface low offshore will drive rain and strong winds on the south and west coasts with heavy falls possible. Small hail and thunder also for inland areas. Showers on the NSW coasts easing during the day, but developing along the central QLD coast as winds turn easterly.

GFS 00z run - 500mb/18000ft flow pattern - Valid Friday 28th May 2021. Tuesday

The high pressure system over the east remains slow moving resulting in the upper low and deep surface low over southern WA will be slow moving so areas of rain, locally heavy over the south coast between Albany and Esperance with widespread showers, hail and thunderstorms for the remainder of the central and eastern SWLD. Easing conditions about the west coast. Finally the dry surge has arrived in the Top End with lower humidity values and cooler day time weather. Note, this is the period where the confidence in weather forecasting becomes low with the upper low deviating from the westerly wind regime.

GFS 00z run - Surface Pressure Pattern and Rainfall - Valid Friday 28th May 2021. Tuesday

A low pressure system off the south coast of WA will drive areas of rain, locally heavy. Showers in southerly winds for the west coast of WA will sit parallel to the coast but some could be wintry with hail and thunder. Scattered showers and thunderstorms developing over the remainder of the SWLD in the afternoon with local hail possible. A rogue shower for the NSW coast and a few showers about the central and northern QLD coasts. A possible shower about Arnhem Land. Dry elsewhere.

GFS 00z run - 500mb/18000ft flow pattern - Valid Friday 28th May 2021. Wednesday

The upper low in this run is further south with a zonal westerly flow over northern Australia, tapping into moisture sitting over the Indian Ocean. There may be extensive cloud developing over the north of Australia which would spread into the NT and northern and western QLD. If the upper low is too far south, then the rainfall will be limited. On this current guide, showers would ease for the south coast of WA with a ridge also nosing in from the west. Showers and the chance of thunderstorms for western SA will move into central SA during the afternoon and reach Adelaide by evening. Light to moderate rainfall expected at this time. A weak trough over VIC and TAS may also kick off some cloud and isolated showers ahead of that system in SA. Dry along the east coast.

Precipitable Water Values Anomalies - Next Wednesday 2nd June 2021.

Showing that moisture layer over the north and the west, and some of it coming into SA with that upper low and trough, but it does appear to be out of phase for widespread soaking rainfall for a number of days at this time for southern and eastern areas. And because the trigger is further south that moisture over the NT and WA will likely be more cloud than rainfall.

Euro Simulated Cloud Forecast Valid Friday 28th 2021.

Showing that moisture being drawn across the country but because the trigger is so far south, broad and weak, the rainfall would not be widespread nor would there be as much impact on temperatures at this stage, however this could easily change and we will know more by Sunday night or Monday.

GFS 00z run - Surface Pressure Pattern and Rainfall - Valid Friday 28th May 2021. Wednesday

The low pressure system begins to weaken and open up into a trough as it approaches the southeast. Rain and a thunderstorm possible in central and southern SA with mainly light falls. Cloud increasing through NSW and VIC with some late rain for the west of the state, mainly at night. Showers easing over southern WA as the air stabalises. Showers becoming more scattered along the QLD coast. A rogue shower over Arnhem Land in the NT. Dry elsewhere.

GFS 00z run - 500mb/18000ft flow pattern - Valid Friday 28th May 2021. Thursday

The latest GFS run wants to open the upper low into a trough and have it carried through the southeast more mobile attached to the front that will ride over the southeast later in the period. This would see patchy rainfall move from SA into NSW and southern QLD, with light falls for now. Showers and drizzle for western Tasmania and Victoria with light falls at this stage. Dry over the west. It could be quite cloudy over northern Australia with significant temperature anomalies.

GFS 00z run - Surface Pressure Pattern and Rainfall - Valid Friday 28th May 2021. Thursday

Areas of rain over western and central NSW and VIC progressing eastwards, with light falls expected. Scattered showers developing over the southeast as southerly winds develop. Local thunder is possible about the southeast SA coast and southwest VIC coast. Isolated showers over the QLD coast to continue. Late rain developing for the Pilbara and Gascoyne coasts with overcast skies spreading throughout northern Australia. Dry and sunny over southern WA.

GFS 00z run - 500mb/18000ft flow pattern - Valid Friday 28th May 2021. A week from today.

The upper trough and front moves further east, sharpening a little over eastern NSW and QLD with a burst of showers or patchy rainfall attached. Southwest winds aloft over the southeast will see another weak front move through overnight Thursday into Friday with more showers. Ridging moving in quickly behind this front will clear skies over SA and keep WA nice and dry, sunny and mild to warm with easterly wind turning northerly. Over the Top End, the warm days should be back with heights coming up.

GFS 00z run - Surface Pressure Pattern and Rainfall - Valid Friday 28th May 2021. A week from today.

Areas of rain over eastern NSW and southern QLD continuing to progress east with light to moderate falls. Showers and some thunder for the southeast with another trough passing through. Rain developing over the Pilbara and Gascoyne with the next shot of moisture coming down the pipe via the jet stream. Fine and dry elsewhere, with warmer weather over the west.

The rain lifts off the east coast by the time we get to the end of Friday with clearing skies and drier air moving in. Patchy rainfall continuing to move in from the Indian Ocean over inland WA and thick cloud possibly developing once again over parts of the NT. Colder southerly winds filtering through the east, warmer northeasterly winds for the west.

It is a low confidence forecast as we track through the coming few days, so expect the modelling to chop and change as we go, which is to be expected.


Back to the weekend schedule tomorrow for these national weather pictures, so one post Saturday and one post Sunday.


Information on the severe weather event for WA will be updated on Saturday morning as will information for the NSW severe surf event and frost issues for the southeast.


If you require more weather information, please email me at karllijnders@weathermatters.org to find out how I may be able to help you.







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