Survival guide: How to stay safe on critical bushfire day
Firefighters are preparing for a worst-case scenario where the behemoth Gospers Mountain bushfire meets the fast-moving Green Wattle Creek blaze in the Blue Mountains.
The biggest fire in the state, Gospers Mountain has burned through more than 400,000 hectares north of the Blue Mountains National Park while the Green Wattle Wattle blaze ripped through the land just south of the national park.
At their closest the fires were within 25km of each other.
North westerly winds will push the Gospers Mountain blaze down towards Katoomba and even closer to Green Wattle by midday.
"The wind speed and direction will shift throughout the day, this alters both the temperatures and the humidity," Bureau of Meteorology Spokesman Neil Bennett said.
"From 11am to 2pm the temperatures will hover around the mid 30s with 35C expected at 2pm. We're looking at wind speeds of about 40kmph starting at 11am, this then drops to 35 after about an hour."
The Rural Fire Service has conceded that they were not able to fully contain either the Gospers Mountain or Green Wattle Creek fire despite their best efforts this week.
After 2pm there will be a dry westerly wind shift that will push both the fires toward Sydney with temperatures still high in the mid 30s.
Conditions will start to ease around 8pm when a southerly shift begins. This will bring a drop in temperature and a rise in humidity.
TOXIC HAZE BLANKETED SYDNEY
A health expert is urging people in smoke-choked parts of Sydney to stay inside as a toxic haze the equivalent of smoking 20 cigarettes and counting worsens by the hour.
The level of toxic PM2.5 particles dragged in from the bushfires jumped threefold in just a few hours in Sydney's southwest on Wednesday morning.
The particles, known to enter the bloodstream and cause a host of health problems including breathing difficulties and even cancer, crept quickly through the day - peaking at lunchtime.
The levels increased threefold in a matter of hours from 133 micrograms of particulates per cubic metre at 5am to 378 by 10am.
Breathing in the acrid haze at current levels does the same damage to your health as smoking nearly a pack of cigarettes, according to Dr Brian Oliver, an air quality expert at the University of Technology.
"Once levels reach 50 people should take notice. There is a significant health effect even if levels are non-hazardous and any day hazardous people should be careful and stay inside," Dr Oliver said.
The levels of the insidious particles were highest in Sydney's south west, the Central Tablelands and North West Slopes, all well beyond levels considered "hazardous" - like smoking 20-30 cigarettes.
The Bureau of Meteorology's Elli Blandford said the plumes of smoke were dragged in today by a westerly buster travelling from the mega-fire razing the Blue Mountains.
"We have quite a lot of smoke in the atmosphere at the moment. We have some winds out there from north or north west dragging some of the smoke over parts of Sydney particularly in the south west."
The haze comes just a day after health experts issued a stern warning for people to stay inside or wear P2 masks when air quality is very poor or hazardous given the risk of long-term health problems like cancer or asthma.
The haze will shroud most of Sydney tomorrow, according to the BOM, until a southerly buster flushes out some of the air in the afternoon before it returns on Saturday.
The NSW Department of Environment says the haze has been the longest and most widespread event ever recorded.