Sydney's Tropical March: Record Heat and Humidity Grip the City
Sydney has been experiencing a prolonged period of abnormal humidity, with moisture levels in recent weeks comparable to Queensland's southern tropics during the wet season. This has made March feel several degrees warmer than the actual temperature.
Sydney has been experiencing a prolonged period of abnormal humidity, with moisture levels in recent weeks comparable to Queensland's southern tropics during the wet season.
While a southerly change is expected to bring temporary relief, a near-record warm Tasman Sea is anticipated to maintain warm and muggy weather well into autumn. This trend is becoming increasingly frequent as the sub-tropical climate zone shifts south.
March Temperature Records
If March were to conclude today, it would mark the hottest on record for both minimum and maximum temperatures at Observatory Hill, with data extending back to 1859. The city's mean daily high for the month has been 27.9 degrees Celsius, and overnight lows have averaged 20.8C, both 3C above the long-term average. When combined with high humidity, the apparent temperature has averaged a peak of 32C in areas sheltered from wind.
Atmospheric Moisture Levels
The dew point temperature, a direct measure of water vapor in the air, indicates that Sydney's average dew point temperature for March is 20C. This is 4C above the long-term March average and 2C higher than Brisbane's average for this time of year.
A dew point above 18C is considered oppressive, and above 20C, it is described as muggy and quite uncomfortable, particularly for Sydneysiders.
Contributing Factors to Mugginess
Besides climate change, two primary factors contribute to the current sticky heat:
- Northerly Winds: Recent weeks have seen a deviation towards northerly winds, which transport tropical air south, leading to above-average temperatures and moisture.
- Warm Tasman Sea: The Tasman Sea off the NSW coastline is currently up to 3C warmer than normal. Warmer waters directly heat the air above the surface and contribute additional water vapor to the atmosphere through evaporation. Onshore winds then carry this moisture over land.
Short-Term and Long-Term Outlook
A southerly change is projected to temporarily lower Sydney's dew point to a range of 10 to 15C. However, north-easterly winds are expected to elevate dew points back to around 20C early next week.
Modeling suggests the Tasman Sea will remain significantly warmer than average throughout autumn, contributing to higher-than-average dew point temperatures until cooler offshore winds become predominant around June.
Climate Shift Projections
Sydney's mean annual temperature has increased by approximately 1.5C over the past century, reaching 19C. This places Sydney's current climate halfway towards Brisbane's early 20th-century climate of 20.5C.
Under a high emissions scenario, Sydney's climate is projected to continue trending towards a more tropical state in the coming decades.
By 2050, Sydney's climate could resemble the NSW Northern Rivers region, and by 2090, the Wide Bay and Burnett Region in south-eastern Queensland.
Climate change involves more than just increased average air temperatures; it also includes shifts in pressure patterns, precipitation, wind, extreme weather events, and atmospheric moisture. Onshore winds in Sydney are becoming more frequent, and they carry more moisture as Tasman Sea waters have warmed at a rate 50 percent above the global average. Additionally, air can hold 7 percent more water vapor for every 1C increase in temperature. Data from Sydney Airport indicates a statistically significant increase of 0.81C in annual average 9am dew point temperature since 1970.