NATIONAL WEATHER PICTURE - SATURDAY 29TH MAY 2021

Headlines


  • Rain and storms continue for the west

  • Heavy seas and strong winds for the east coast.

  • A run of near record cold May nights for the southern and eastern inland.

An active period of weather continues out west with a trough and upper low combining with large amounts of tropical moisture to bring widespread showers and thunderstorms into the west coast. Overnight we have seen multiple rounds of showers and storms, with heavy rainfall leading to pockets of flash flooding. That will continue throughout Saturday for a wide area of western and southern WA.


Rough to even violent seas off the east coast causing some significant beach erosion along southern facing beaches in NSW, in combination with astronomical high tides. Some coastal flooding has also been observed along the Mid North Coast and Hunter regions this morning with waves in offshore waters exceeding 10m.


Overnight we had temperatures down as low as -7C at Goulburn and widespread severe frosts reported across NSW and northern VIC with light winds, clear skies and a dry airmass. The run of severe frosts will continue into Sunday and Monday. Near record minima possible on both days.


National Satellite Picture - Valid Saturday 29th May 2021.

Relatively clear skies across the southeast and east with sinking air motion under a strong upper ridge. That is contributing to the very cold May nights but lovely sunny days across most of eastern Australia at the moment, away from the coast. Low cloud in the Tasman is moving rapidly north into the low near NZ, causing light showers along the NSW coast. Out west an active trough is producing widespread cloud, with showers and thunderstorms erupting along the axis of the trough and rotating around a developing upper low. High cloud over the interior which brought light rain to WA yesterday is all but torn apart by the high pressure.

A closer look at the Tasman Sea showers how vigorous that low pressure system is, with significant areas of rain and thunderstorms swirling around the centre of circulation near Auckland. On the western flank of that low towards Australia, gale force southerly winds and heavy seas continue for Saturday but will begin to ease on Sunday as the low becomes progressive to the east.

Out west the most active weather across the nation will be here. Overnight, widespread rain has developed from moisture that was over the Indian Ocean, now drawn into the trough and upper low and being lifted into convection. Some storms could be severe through the region today with heavy rainfall and damaging winds. Rain will spread further inland and to the east over the coming 24-48hrs. Along the south coast, potential for heavy rainfall to develop over the coming few days with a low meandering along the coast.

Temperatures have been absolutely freezing over the south and east overnight with near record values in some locations and a heavy frost. Milder further along coastal areas where there is more wind at the moment along the east and south coasts. Warmer over northern Australia, with the afternoon seabreezes just allowing some surface moisture to building during the afternoon and evening and being trapped in the inversions. Out west, thick cloud cover and widespread rainfall keeping temperatures up.


Temperatures as of 7am EST Saturday 29th May 2021

Over the southeast, this is a sign of what is to come, with those sub zero temperatures spreading west and south over the coming days, with locally severe frost across multiple states expected.

Frost forecast for Sunday Morning - Valid Saturday May 29th 2021.

A freeze is possible about parts of the east on Sunday - with overnight temperatures below -5C for more than 8hrs. Pipes will burst under these conditions.

Frost Risk - Monday Morning - Valid Saturday 29th May 2021.

Some record low minima may be observed during Sunday and Monday morning.

Out east, the waves have continued to rise overnight with active wave heights of 6-8m in offshore waters, some buoys out in the Tasman recording 10-12m wave heights overnight, with gale force southerly winds. Hazardous surf warnings and severe weather warnings remain in place for Saturday before conditions slowly ease Sunday. Again with the southwest flow of the currents, south facing beaches will cop the brunt of it. A new wave of heavy surf is moving through the southern ocean this week and will bring heavy conditions to southern Australia.


Wave heights forecast for Saturday morning - Valid Saturday 29th May 2021.

Thunderstorms will be active over WA again on Saturday with some chance of them turning severe with heavy rainfall leading to flash flooding. Damaging winds cannot be ruled out either. The thunderstorms will flatten out into areas of heavy rainfall later today and move inland during Sunday and redevelop along the south coast with low pressure.


Thunderstorm Forecast - Saturday 29th May 2021.

90% chance 9/10 chance of thunderstorms developing within 25km of a given point during Saturday afternoon in the pink zones. The risk tapers down to 50% for yellow and 10% for white.

Flash flooding is a risk on Saturday into Sunday throughout the western parts of WA with thunderstorms the biggest risk of producing flash flooding. A low winding up along the south coast will also increase the risk of flash flooding during Sunday and Monday with wrap around bands of heavy rainfall.


Flash flood risk - Saturday 29th May 2021.

Risk Rating of flash flooding developing within 25km of a given point.

Low = 5-30% Moderate = 30-50% High= 50%-80%. Very High= 80-95%

Rainfall for the next 10 days remains low confidence away from the west coast of Australia with that upper low deepening in the coming days. How that lifts out and if it tracks east or southeast will determine how much rainfall does develop over the east.


GFS Rainfall - Next 2 weeks. Valid May 29th 2021.

CMC Rainfall Next 10 days - Valid Saturday May 29th 2021.

Rainfall again concentrated on the path and connected to the scale and intensity of the upper low and whether it will be absorbed with the upper flow pattern to the south, or cut off and move north of the westerly wind belt and avoid capture by weak cold fronts over southern Australia.


Rainfall Forecast - Next 10 days - Valid Saturday May 29th 2021.

Higher confidence for rainfall exists over the west, with lower confidence in rainfall further west with the remains of the severe weather event over WA.

Synoptic Discussion.


GFS flow pattern at 500mb/18000ft - Valid Saturday 29th May 2021. Saturday

Strong upper low over the Tasman Sea with a number of surface low pressure systems rolling underneath the system will continue to produce violent surf and gale force winds to the NSW coast. Another developing upper low over WA will produce widespread rain and thunderstorms on Saturday, some heavy falls possible. Otherwise after a cold start fine and sunny weather for the remainder of the nation.

GFS 12z run Surface Pressure Pattern with rainfall distribution - Valid Saturday 29th May 2021. Saturday.

Widespread rain and thunderstorms for the west with moderate to heavy falls possible, otherwise the rest of the nation mostly dry with high cloud streaming through inland WA ahead of the rain. In the east, scattered showers along the Central and Hunter coasts with gale force southerly winds and high surf easing later. Cold nights returning through eastern inland Australia tonight with near record values possible.

GFS flow pattern at 500mb/18000ft - Valid Saturday 29th May 2021. Sunday.

A very cold start for inland areas of Australia's south and east with near record low values expected over NSW, VIC and eastern SA. Sunshine to follow under a ridge. The east coast will see the wave heights ease and winds drop below gale force. Rain and thunderstorms to continue over parts of WA with an upper low moving along the south coast and a surface low forming offshore. Gale force winds and heavy rainfall may develop along the south coast. The high amplitude pattern will remain slow moving.

GFS 12z run Surface Pressure Pattern with rainfall distribution - Valid Saturday 29th May 2021. Sunday

Rain and thunderstorms contracting the south coast of WA with showers in remaining districts. Some locally heavy falls are possible about the south coast between Albany and Hopetoun. Showers may develop along the QLD coast north of Mackay as winds veer into the east as the high moves further east south of the state Showers clearing for the NSW coast with easing winds. After another near record cold start over the SE inland, a sunny bright Sunday coming up. Fine through central areas with temperatures warming in a northerly flow.

GFS flow pattern at 500mb/18000ft - Valid Saturday 29th May 2021. Monday

Upper low over WA begins to lift east northeast with a surface low attached underneath also riding the south coast, bringing showers, areas of rain with moderate to heavy falls and strong winds. Ahead of the low, cloud increasing over SA with late rain for the western districts. Fine in the east after again, near record cold starts for inland NSW, VIC and eastern SA. The east, will see the showers decrease and fine weather return to NSW coastline with the low lifting out east of NZ. Heat levels coming down over the northern parts of the nation.

GFS 12z run Surface Pressure Pattern with rainfall distribution - Valid Saturday 29th May 2021. Monday.

Rain at first for the south coast of WA, tending to showers during the day with lingering moderate falls easing. Otherwise the majority of the country is rain free, apart from the eastern Top End of the NT with rogue showers coming off the GoC and a few showers in the easterly winds over the coast north of Bowen in QLD. Again after near record cold starts sunshine for the east and southeast, though daytime temperatures will move above the average over SA in a northerly flow. Cloud increasing over SA and the western and southern NT later as well as the Pilbara coast of WA with an approaching trough.

GFS flow pattern at 500mb/18000ft - Valid Saturday 29th May 2021. Tuesday

Upper low weakening over waters south of SA on Tuesday, but cloudy skies over western districts with patchy rain, maybe some thunder possible. A ridge in the east is progressive and moving over the Tasman Sea making room for the low to move eastwards. A ridge building over WA will clear skies from the west. Heat levels continue to come down over northern Australia, though there may be some cloudy skies. Another trough is approaching the northwest coast of WA.

GFS 12z run Surface Pressure Pattern with rainfall distribution - Valid Saturday 29th May 2021. Tuesday

Cloudy skies through most of SA with patchy rainfall about, with mainly light falls expected. Dry over much of WA after morning showers and drizzle about the far east coast near the Eucla clear through the day. A few showers possible over the coast from Mackay to Cooktown in QLD but most almost the rest of the nation dry after another cold start in the east, though northerly winds developing will warm the days more efficeintly.

GFS flow pattern at 500mb/18000ft - Valid Saturday 29th May 2021. Wednesday

Upper low drifts east to be over Adelaide on Wednesday with cooler conditions and an increase in the chances of rainfall. A new ridge over the west will see a return to fine days for WA after cold starts inland with morning frost. Ridge breaking down over the Tasman Sea will contribute to more cloudy skies for eastern areas ahead of rain moving in later in the day from the west. Heat starting to rebuild over the northern states.

GFS 12z run Surface Pressure Pattern with rainfall distribution - Valid Saturday 29th May 2021. Wednesday

The low pressure trough will deepen a fraction over eastern SA thanks to shortwave moving through the SE, and more moisture over the eastern districts providing better coverage of rain over eastern SA, western NSW and southwest QLD during the day, spreading through VIC by afternoon and into Central NSW by evening. Light falls for the most part but these could pick up overnight into Thursday over central NSW. Fine in the west, though cloud increasing with rain sitting just offshore the Pilbara and Gascoyne once again. Drying out over much of QLD with a stabalising atmosphere.

GFS flow pattern at 500mb/18000ft - Valid Saturday 29th May 2021. Thursday

Upper low deviates from the easterly track and moves in conjunction with a shortwave over southeast Australia to the northeast. This sharpening the feature a little. It will also feed into higher moisture levels coming in from the northwest of the nation to produce widespread cloud over a large chunk of the north and east. Ridging over WA will keep the skies clear and sunny for the SWLD.

GFS 12z run Surface Pressure Pattern with rainfall distribution - Valid Saturday 29th May 2021. Thursday

Rain areas of central NSW, contracting through northern NSW and developing over southern inland QLD during the morning before moving towards the coast by afternoon. Light to moderate falls are anticipated. A weak cold front passing over the southeast may produce light showers and cloudy skies. Out west, a new wave of tropical moisture will see rain developing over the Pilbara and northern Gascoyne with moderate falls possible about the coast. Warming up south of that through the SWLD with easterly winds.

GFS flow pattern at 500mb/18000ft - Valid Saturday 29th May 2021. Friday

Upper low over QLD/NSW border will continue to move steadily northeast, with cloud and rain progressing through the east and north. Ridging building over much of southern Australia with clearing skies over the inland and warmer weather for the west. Zonal flow over the Southern Ocean beginning to pick up speed and may promote cold fronts to push northwards later in the period into next weekend.

GFS 12z run Surface Pressure Pattern with rainfall distribution - Valid Saturday 29th May 2021. Friday

Rain at times for the northwest of Australia with a pulse of tropical moisture off the Gascoyne and Pilbara coasts. Thick cloud pushing through WA and into the NT with this jet stream but stable air keeping things dry for now. Over the east, the upper low deepen further offshore with a new surface low increasing rainfall rates for southeast QLD and northeast NSW. Some thunder is also possible. The remainder of the nation is dry under a broad ridge stretching from Perth to Canberra.

GFS flow pattern at 500mb/18000ft - Valid Saturday 29th May 2021. 10 days from now.

Upper low moved well off the QLD coast, however a trough over inland areas may still bring cloudiness and rainfall to QLD and the NT. A new cold front and trough pushing through SA and VIC may produce a burst of colder weather and rain periods. High pressure on both of the nations will keep conditions settled over the west coast with cold nights.

GFS 12z run Surface Pressure Pattern with rainfall distribution - Valid Saturday 29th May 2021. June 7th 2021.

Cold front moving through the southeast with scattered showers and gusty winds. Limited moisture with this feature would mean rainfall totals would be light and restricted to coastal areas. Showers over parts of Cape York through the morning with a weak southeasterly surge moving over the northern parts of the nation. Isolated showers with a pre frontal trough over NSW and QLD would nett light falls under this scenario. Fine out west with a strong high southwest of Perth. But this is 10 days out and will likely change by the next run.


So overall it is a typical late Autumn pattern as we see the final cogs turn towards the deep winter flow pattern over southern Australia which is still a few weeks off. The official start of winter is not really until the Solstice in about 4 weeks time.


Next broad update will be Sunday afternoon as I am on my weekend schedule.


If you need more forecasts for the week ahead and want some tailored forecasting solutions, this is the time to place you orders - email me at karllijnders@weathermatters.org for more details.


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