Showers and thunderstorms developing for WA
Significant increase in surf off the east coast of NSW.
Settled skies elsewhere with cool conditions in the southeast.
A trough deepening off the WA coast has flared thunderstorms overnight with patchy rainfall over the Pilbara and Gascoyne overnight. Further thunderstorms have developed in recent hours off the west coast and these are expected to increase further during Friday.
A powerful cold front is in the process of rolling through the Tasman Sea on Friday morning with squally southerly winds and significant southerly swell impacting the NSW coast. Hazardous surf warnings are in place for the largest wave event of the year so far.
With the high amplitude pattern across the region, a strong ridge separates the long wave troughs on either side of the nation. That ridge is keeping the majority of the nation settled, though scattered showers and drizzle falling over southeast areas of VIC and western TAS in the onshore flow.
National Satellite Picture - Valid Friday May 28th 2021.
Cold front approaching WA has significant shower and thunderstorm activity along its axis. Tropical moisture being drawn into the jetstream with showers falling along the Pilbara coastline. High cloud over inland WA and SA is fair weather and producing no rainfall. Speckled cloud cover is rotating through the Tasman Sea with a strong cold front barreling northwards this morning. Low cloud over southern VIC and western TAS is producing light showers.
Cold front rolling through the Tasman is producing significant wave heights over the region with damaging surf developing along the east coast today as this feature wraps into a deep low pressure system later today and into Saturday. Gale force winds will remain active along the coast with gusts near 100km/h in offshore waters.
Trough approaching the coast with a cold front behind is producing thunderstorm activity this morning offshore. Showers and thunderstorms will increase in coverage during the day with some moderate to heavy falls developing with thunderstorms. Severe weather is unlikely at this time.
It has been another cold start under the high pressure ridge over central and eastern inland parts of Australia. Skies have been mainly clear with light winds allowing that radiational cooling to continue quite nicely. Elsewhere, cloud cover and more wind overnight has kept temperatures above average. Parts of VIC and TAS have seen very little movement in overnight to day time temperature due to thick cloud cover during the past 72 hours. After a cold start over the inland regions, back to seasonal conditions for most, some areas over NSW and the southern NT and inland WA under cloud, may remain below average today.
National Temperatures - Valid 6am EST Friday May 28th 2021.
It has been cold from Alice Springs through to the GDR with local frost also occurring in parts of southern QLD and about the Central Highlands this morning.
Rainfall for the next 10 days carries a high confidence for the west and a low confidence for the east. A large high over the east will keep most of the nation dry for the next 4-5 days, while the wettest part of the nation will be over the west of the nation with a trough, cold front then a low pressure system developing. That low may lift out as an upper feature into SA and the eastern inland next week, but pinning down the impact of that is undetermined at this time.
Rainfall for the next 10 days - Valid Friday 28th May 2021.
CMC 12z Run - Valid Friday 28th May 2021.
Showing patchy rainfall mainly over QLD with that upper feature moving east. Heavy rainfall is a high chance over the west coast with some parts of southern WA possibly getting as much as 200mm on this guide.
Euro Rainfall for the next 10 days - Suggesting more widespread patchy rainfall for the east mid to late next week. But the higher confidence is in the rainfall out west with heavy falls possible about the south coast of WA. Euro 12z run rainfall for the next 10 days Valid Friday May 28th 2021.
GFS 12z run - Rainfall for the next 10 days - Valid Friday May 28th 2021. Patchy rainfall moving east with the trough or upper low but only light falls with low confidence. Heavy rainfall out west carries a high confidence.
The broader synoptic scale is dominated by high pressure over southern parts of the nation, ridging into the east. A fast moving flow pattern over TAS and VIC underneath the ridge is producing light rainfall but has birthed that very powerful system in the Tasman Sea which will cause gales and significant waves over the weekend.
The high amplitude pattern is also strengthening the trough and cold front over the eastern Indian Ocean, causing showers and thunderstorms to flare this morning offshore with that activity expected to crash land today and stick around for a number of days, thanks to a low forming in the SWLD.
With the high becoming slow moving over the weekend and next week over the east, it will slow the progression of the low pressure over WA, meaning a multi day rainfall event will take place with some significant rainfall totals anticipated over the south coast of WA during the latter part of the weekend into next week. Widespread rainfall over inland WA could nett another month's worth of rainfall.
Over the north, heat levels should come down with a drier airmass moving in.
GFS 500mb flow pattern - Valid Friday May 28th 2021. Friday
High amplitude pattern developing over Australia with a deep low over the Tasman Sea producing that gale force wind event and significant wave heights. Strong upper ridge controlling the majority of the nation with clear skies over the inland with temperatures near seasonal for most, away from cloud. A new trough approaching the west will help to develop those showers and thunderstorms further with a northwest flow aloft.
GFS 500mb flow pattern - Valid Friday May 28th 2021. Saturday
Deep low over the Tasman Sea will see wave heights peak to dangerous levels on Saturday morning at around 10m in offshore waters near NSW. That low with the gales and heavy showers will slowly move east later. Strong upper ridge over the south and east of the nation controlling weather for the weekend. A front and upper low begins to make landfall over the SWLD with rain and thunderstorms pushing in along the west coast and extending inland to the Wheatbelt with moderate to heavy falls possible.
GFS 500mb flow pattern - Valid Friday May 28th 2021. Sunday
Deep low over NZ will move away during Sunday with waves and winds easing over the NSW coast. Showers will also decrease along the coastal fringe. Upper ridge over southeast Australia will lead to a very cold night Saturday into Sunday with sinking air, clear skies, some significant frost is likely. A deepening low over the SWLD of WA will continue to drive widespread showers and thunderstorms with areas of rain about the south coast with moderate to heavy falls. Severe weather is possible about the south coast of WA during Sunday.
GFS 500mb flow pattern - Valid Friday May 28th 2021. Monday
A deep low continues to drive widespread showers and thunderstorms over southern WA with areas of rain on the western side of low pressure leading to areas of flash flooding about the south coast of WA. A high in the east will continue to produce cold nights with morning frost but sunny days to follow with temperatures still scraping to seasonal values. The low in the Tasman opens into a wave east of NZ with little impact over the NSW coast at this time, but waves could still be powerful even though they are reduced in height. Heat levels over the Cape York and the NT should be reduced by this time with drier air moving in.
GFS 500mb flow pattern - Valid Friday May 28th 2021. Tuesday
Upper low beginning to lift out of southern WA and moving into southern SA with the showers and some thunder moving from the southwest of WA to the east during the day, though overall wet along the south coast. Clearing along the west coast of WA with southerly winds easing. A ridge in the southeast, continuing to drive cold nights and fine sunny days, but with the winds tending into the north, the weather should begin to warm up. More dry weather for the northern parts of Australia. Cloud may begin to increase over central and eastern inland areas during the day which could lead to below average temperatures.
This is an example of that cloud impact on temperatures - mid next week. Valid Thursday May 27th 2021. With thick cloud cover, not just the potential of rainfall, temperatures could be 12-15C below average over the north!
Precipitable Water Values - GFS 12z Run Valid Friday May 28th 2021.
Deeper moisture being analysed to stream into the interior thanks to that weakening upper low lifting out of WA into SA. The track of this low will determine how much of this precipitable water gets utilised into rainfall. Could be just thick cloud if the low is too far south and is absorbed into the frontal weather, could be a lot if the low is cut off and moves more north of the westerly flow.
GFS 500mb flow pattern - Valid Friday May 28th 2021. Wednesday
Upper low over southern SA opens into a wave and gets captured by a cold front over southeastern Australia. However other runs in this particular model have taken the low further north and cut it off from the westerly, so this is where we see the forecast confidence become very low. New ridge over WA brings fine weather to southwest and west of the nation. Zonal flow over the north of the nation with higher levels of upper level moisture will see cloud increase over the NT, QLD and northern NSW with potentially some rainfall about, but more likely well below average temperatures.
Precipitable Water Values - GFS 12z Run Valid Friday May 28th 2021.
High levels of PW over northern Australia riding the jet stream over northern WA, NT and into QLD. Some of the values are 40-50mm over WA and into the NT, however on this run, you can see the impact of the low pressure further south and not able to drag in that high moisture content, leading to less rainfall in the GFS rainfall forecast this morning. But I stress this will change over the coming days, with this model yesterday showing 50-100mm for parts of QLD and NSW.
GFS 500mb flow pattern - Valid Friday May 28th 2021. Thursday
Upper low is absorbed into the frontal wave over southeast Australia bringing light rain and cooler conditions through the south and east. More cloudy skies over northern Australia with the upper levels quite moist with the jet stream dragging into moisture from the Indian Ocean, but with the lower and middle levels dry, rainfall under this scenario would be non existent. Ridging moving south of WA will see warmer and sunny weather for the west.
GFS 500mb flow pattern - Valid Friday May 28th 2021. Taking it out 10 days to Sunday June 6th 2021.
Another long wave approaching the southeast of the nation but the main thrust and dynamics well south of the nation will mean showers restricted to southeast SA, VIC and TAS. Not much making it into NSW. Dry out west with a ridge of high pressure and seasonal temperatures persisting over northern Australia after the cloud moves further east and offshore QLD later in the day with an upper trough. But this 10 days out and will likely change.
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