By ABC meteorologist Tom Saunders
Extreme fire danger has been forecast for NSW on Wednesday. Photo: ABC / Adriane Reardon
Eastern Australia is facing a barrage of extreme weather conditions this week, and for many areas the most intense conditions will arrive on Wednesday.
Firstly, a prolonged heatwave from the outback to the east coast is leading to the highest November temperatures in years, including in both Sydney and Brisbane where respective highs will exceed 35 degrees Celsius on Wednesday and Thursday.
The hot, humid conditions are also fuelling destructive thunderstorms, with the further risk of large hail, heavy rain, and damaging winds during the coming days.
In addition to storms, a separate weather system sweeping over southern and central NSW will whip up strong, dry westerlies on Wednesday, a recipe for downed trees and fast-moving fires.
NSW fire threat to spike in dry westerly gales
Wednesday's weather across NSW represents a nightmare for fire authorities thanks to baking heat, strong winds, low humidity and drying soils.
The sudden increase in wind will result from a sharp boundary between hot north-westerly winds from the interior and cooler air from the Southern Ocean.
Gusts up to 100 km/h are likely in south-east NSW, strong enough to down branches and possibly entire trees which brings the risk of property damage and power outages.
The arrival of an outback air mass will also send temperatures skyrocketing while dropping humidity well below 20 percent.
Sydney is set for a hot day on Wednesday. Photo: ABC / Liam Patrick
The Bureau of Meteorology (BOM) has therefore forecast extreme fire danger, the second-highest rating, in 10 districts on Wednesday, including the Greater Sydney region.
A catastrophic fire danger, the first of the season in NSW, is predicted for the Lower Central West Plains.
During days of extreme or catastrophic danger, bushfires can become fast-moving and uncontrollable, while flying embers can ignite spot fires several kilometres ahead of fire fronts
Further enhancing Wednesday's threat around central parts of NSW is lightning strikes which could start new blazes.
Another burst of dry, gusty westerlies will arrive across NSW on Thursday, leading to a second day of extreme fire danger around the Hunter, Sydney and Central Ranges.
An extreme fire danger is also expected in Queensland's Darling Downs on Thursday, while extreme dangers should return to parts of NSW on Saturday when the next burst of hot, dry winds arrive from the interior.
Hottest November weather in years
Australia's interior has been baking in the mid-40s in recent days, and several towns came within a fraction of a degree of a spring record on Monday, including highs of 45.7C at Longreach and 46.1C at Windorah - the hottest November maximum in 19 years for both towns.
Blistering temperatures continued over the outback on Tuesday. However, the westerlies are also carrying the inland heat to the coast.
The BOM's heatwave warning therefore extends across most of Queensland and northern NSW, including some regions with an extreme rating - the highest category which indicates dangerous conditions, even for otherwise healthy people.
Brisbane is sweating through a run of hot and humid days in the mid 30s and is expected to peak at 37C on Thursday, the highest November maximum in seven years.
With the city's nights bringing little relief, Brisbane is analysed by the BOM as being in a severe heatwave, the second-highest severity.
Sydney is only seeing a low intensity heatwave due to cooler nights. However, the forecast on Wednesday of 36C is 12C above average and will be the city's warmest November day in five years.
While outback temperatures are now cooling, the prevalence of westerlies will maintain the current heatwave over eastern Queensland and north-east NSW into the weekend.
Modelling is currently showing cooler air from the south should finally spread up the east coast about Tuesday and Wednesday next week.
Daily dose of wild afternoon storms
Powerful supercell thunderstorms hammered south-east Queensland and north-east NSW on Monday, including hail up to 14 centimetres in diameter around Brisbane in the afternoon.
Very intense thunderstorms again fired up on Tuesday.
However, on this occasion they were focused more over the inland, producing winds up to 125 km/h around Tamworth, along with gusty winds and damage in Dubbo.
The ongoing heat and humidity will again prime the atmosphere for thunderstorms on Wednesday along much of the eastern seaboard.
A jet stream aloft will supply a source for further damaging gusts across NSW and southern Queensland, while the odd supercell is also possible in north-east NSW and far southern Queensland with giant hail and intense rainfall.
The thunderstorm outbreak will continue on Thursday from northern Queensland to far north-east NSW - and again severe storms are likely around south-east and central Queensland.
After 24 hours of respite on Friday when drier air from the interior briefly reaches the coast, the risk of severe thunderstorms will return to south-east Queensland and far north-east NSW this weekend.
-ABC
