Climate of Sydney

The climate of Sydney, Australia is humid subtropical (Köppen: Cfa),^[1] shifting from mild and cool in winter^[2][3][4] to warm and hot in the summer, with no extreme seasonal differences as the weather is moderated by proximity to the ocean,^[5] although more contrasting temperatures are recorded in the inland western suburbs. Despite the fact that there is no distinct dry or wet season, rainfall peaks in the first few months of the year and is at its lowest just around the middle of the year, though precipitation can be erratic throughout the year.^[6][7] Precipitation varies across the region, with areas adjacent to the coast being the wettest.^[8] According to the Bureau of Meteorology, Sydney falls in the temperate climate zone which has warm to hot summers^[a] and no dry season.^[9] Sydney's plant hardiness zone ranges from zone 11a to 9b throughout the metropolitan area.^[10] Under the Holdridge Life Zones classification, eastern Sydney falls in the Subtropical Moist Forest zone and the western suburbs in the Subtropical Dry Forest zone.^[11]

Sydney has 109.5 clear days and 127.2 cloudy days annually,^[12] though it has around 200 days of visible sunshine if partly cloudy days or sunny breaks are counted.^[13] Overall, Sydney has just about 66% of possible sun for Jun-Aug and around 54% for Dec-Feb, making winter sunnier than summer on average, in addition to it being sunny around 65% of the time in the year with its 2,640 hours of annual sunshine.^[14] Sydney's heat is predominantly dry in spring, but usually humid in the summertime.^[15] On some hot summer days, low pressure troughs increase humidity and southerly busters decrease temperatures by late afternoon or early evening.^[16][17] In the warm season, particularly late summer and early autumn, troughs combined with a humid air mass can bring large amounts of rainfall,^[18] and in late autumn to early winter, the city can be affected by east coast lows.^[19] When the subtropical ridge is north of Sydney in late winter to early spring, the wind comes from the west or inland. As the ridge moves south in summer and autumn, the winds become easterly.^[20][21][22]

Sydney experiences an urban heat island effect,^[23] making certain parts of the city more vulnerable to extreme heat, particularly the west.^[23] Efforts have been introduced to investigate and mitigate this heat effect, including increasing shade from tree canopies, adding rooftop gardens to high rise structures and changing pavement colour.^[24][25] The El Niño Southern Oscillation, the Indian Ocean Dipole and the Southern Annular Mode^[26][27] play an important role in determining Sydney's weather patterns: drought and bushfire on the one hand, and storms and flooding on the other. Sydney is prone to heat waves and drought, which have become more common in the 21st century.^{[28][29][30][31]} Furthermore, the region of Sydney, and as well as the rest of the New South Wales coastline, is warmed by the East Australian Current.^[32][33] In 2020, researchers at The Australia Institute discovered that Sydney was experiencing longer summers and shorter winters in recent decades, compared to those in the 1950s and 1960s.^[34] In 2023, Sydney was placed at 9th place by Stars Insider for having the best weather in the world.^[35]

Seasons

Summer

Summer in Sydney tends to vary, but it is generally warm to hot.^[36] Though at times, sea breezes moderate the temperatures and raise humidity. Temperatures tend to be stable in late summer where temperature maximum rarely go below 20 °C (68 °F) or over 40 °C (104 °F), unlike late spring and early summer where such extremes may occur.^[12] Summer is often humid, particularly late summer – However, when temperatures soar over 37 °C (99 °F), the humidity is generally low as such high temperatures are brought by searing winds from the Australian desert.^[37][38] Sydney summers are characterised by rapid changes of weather, with humidity and rain not uncommon in the city although thunderstorms are more common in the west. The ultraviolet index rating in the summer averages at 12, but can reach 13 in the midst of the season, which may lead to skin damage among those having light skin.^[39]

When temperatures reach over 30 °C (86 °F), the relative humidity seldom exceeds 45%, although low pressure troughs can increase humidity in some hot days, especially in late summer, where they may provide afternoon thunderstorms that are usually accompanied by heavy rainfall and, at times, hail. Furthermore, most mornings and nights are muggy, with the 9am relative humidity ranging from 69% to 75%.^[12][40] The average 3pm dewpoint temperature in the summer ranges from 16.2 °C (61.2 °F) at the coast, to 14.4 °C (57.9 °F) inland. Dewpoints are higher in late summer, reaching 20 °C (68 °F), especially in the mornings and evenings, although they are usually lower in the heat of the day, dipping as low as 9 °C (48 °F) in the extremely hot day.^[41]

In late spring and summer, Sydney can sometimes get northwesterly winds from the Outback, which are dry and hot, making the temperatures soar above 38 °C (100 °F), with the relative humidity as low as 15%. This happens after the northwesterlies are carried entirely over the continental landmass, not picking up additional moisture from a body of water and retaining most of their heat. On these occasions, Sydney can experience the fury of the desert climate,^[42] although they are often ended with a southerly buster, which is a windy, shallow cold front that sweeps up from the southeast abruptly cooling the temperature. At times, it may be accompanied by a thunderstorm and drizzle, and it may keep the temperatures cool the following few days as well.^[43] These strong, hot, northwesterly winds from the interior always precede a vigorous, westerly cold front (which usually drags warm inland air towards the southern and eastern coasts).^[44][45]

In the Sydney central business district, an average of 15 days a year have temperatures of more than 30 °C (86 °F) and 3 days with temperatures over 35 °C (95 °F).^[12] In contrast, western suburbs such as Liverpool and Penrith have 41 and 67 days with temperatures above 30 °C (86 °F), 10 and 19 days above 35 °C (95 °F), and, 1 and 4 days above 40 °C (104 °F), respectively.^[40][46]

The highest recorded maximum temperature at Sydney Airport was 46.4°C (115.5°F), which was on 18 January 2013.^[47]

The highest recorded maximum temperature at Sydney CBD was recorded on that same day with the temperature climaxing at 45.8°C (114.4°F).^[48]

The highest recorded maximum temperature within Sydneys Metropolitan area was recorded at Penrith with a high of 48.9 °C (120 °F), a Western Sydney suburb, on 4 January 2020. At that time, Penrith was the hottest place on the planet and the hottest temperature recorded within Australia and the Southern Hemisphere for all of 2020.^[49]

Autumn

Late summer conditions usually continue until the first few weeks of April where maximum temperatures hover between 25 and 29 °C (77 and 84 °F) with the dewpoint being around 16–17 °C (61–63 °F) on average. Although, unlike late summer, the nights may be seemingly cooler and crispier. Most heavy rainfall events usually occur in late summer and early autumn as the subtropical ridge of high pressure, which rotates counterclockwise, is to the south of Australia and therefore give way for moist easterlies from the Tasman Sea and as well as low pressure systems to penetrate the region.^[26][22]

The transition from late summer to autumn is gradual, with noticeably cooler and crisper conditions taking in effect by around mid-April. In mid-autumn, the highs typically average at a pleasant 22–24 °C (72–75 °F), rarely going above 30 °C (86 °F) or below 20 °C (68 °F). In May, the average highs are around 19–21 °C (66–70 °F) with cool and usually humid nights, that seldom dip below 10 °C (50 °F). Wintry highs of 18 °C (64 °F) may be expected in the last week of autumn.^[50]

Temperatures in autumn are usually consistent and stable, lacking any extremes that tend to be experienced in spring and summer. Due to moist easterlies that prevail in this season, foggy mornings should be expected. The average 9am relative humidity in autumn ranges from 72% to 80% in the Sydney region, the highest in the year.^[40]

The lowest maximum temperature in autumn is 11.3 °C (52.3 °F), recorded on 24 May 1904.^[12]

The highest maximum autumn temperature ever recorded at Sydney Airport was recorded on 9 March 1983, with the temperature peaking at 41.2 °C (106.2 °F)^[51]

Winter

Winter in central Sydney tends to be mild where the lows rarely drop below 7 °C (45 °F), mainly due to proximity to the ocean.^[12] Furthermore, Sydney CBD (Observatory Hill) has never recorded frost, whereas coastal cities in the country on similar latitudes, such as Perth, Esperance and Adelaide, and those further north of Sydney such as Coffs Harbour, Hervey Bay, Sunshine Coast and even Mackay, have recorded frost or temperatures below 0 °C (32 °F).^[12]

In the west (or inland suburbs), temperatures are typically around 17 °C (63 °F) in the day and 5 °C (41 °F) at nights.^[40] In the far west (particularly in Richmond and Camden), the diurnal range is relatively great, where temperatures, can be as high as 18 °C (64 °F) in the afternoon and as low as 3 °C (37 °F)^[52][b] at night or early morning, due to the distance from the ocean. With such low temperatures, frost can form in some mornings in the far western suburbs and sometimes and occasionally it can be chilly which also can be cold get around 10 to 15 °C (50 to 59 °F) it fairly common in daytime. ^[53]

In the west, Liverpool and Richmond have 4 and 38 nights, respectively, where temperatures dip below 2 °C (36 °F). On average, only 1 night in Liverpool and 17 nights in Richmond have lows that go below 0 °C (32 °F). Such cool lows in the far west are contributed to by a temperature inversion and a mountain breeze effect caused by the Blue Mountains, which impact the suburbs on their footsteps. The lowest maximum temperature in Liverpool was 8.2 °C (47 °F), recorded on 28 July 1981. Similar low maximums have been recorded in the Sydney region in winter.^[40] 9am humidity ranges from 61% to 74% across the Sydney region, with the more higher figures experienced in June mornings. Highs of 12 °C (54 °F), whilst rare, are not unheard of in winter.^[12][40]

Sydney receives around 15 days of fog annually,^[54] which occurs in winter mornings, but more often in June when moist easterlies dominate. The inland suburbs generally receive radiation fog due to nocturnal cooling under a clear sky of humid maritime air that was brought inland by the previous day's sea breeze. The coastal suburbs mostly get an advective fog, which floats ashore from the meeting of warm water offshore and cold water nearby on the land. Heavier rain and cloudiness are also to be expected more in June, on average, than the latter winter months.^[55]

During late winter, warm dry westerly winds which dominate may raise the maximum temperatures as high as 25 °C (77 °F) in some instances. As the subtropical ridge is north of Sydney in mid-to-late winter, it picks up dry westerlies from the continent's interior because of its anticlockwise rotation, thus producing more sunny days in the region,^[26] hence why August has the highest sunshine percentage of any other month.^[56] In early winter, the UV index averages at 2, which means it is safe to be outdoors unprotected, but it reaches 3 by the end of the season (therefore sun protection is required for the general population).^[57]

The lowest recorded minimum at Observatory Hill was 2.1 °C (35.8 °F) on 22 June 1932,^[12] while the coldest in the Sydney metropolitan area was −8 °C (18 °F), in Richmond. The lowest recorded maximum temperature at Observatory Hill was 7.7 °C (45.9 °F). Although not usually considered a suburb of Sydney, Picton, a town in the Macarthur Region of Sydney, recorded a low of −10.0 °C (14.0 °F) on 16 July 1970.^[58]

Spring

Early spring is rapidly transitional. Cool conditions from late winter may continue in September with the maximum temperature dipping as low as 18 °C (64 °F) at the coldest, but due to the drastic transition, temperatures above 30 °C (86 °F) can also be expected in that month. By November, summery conditions begin, with temperatures normally ranging between 24 °C (75 °F) and as high as 30 °C (86 °F), albeit with relatively low humidity.^[60]

Because the subtropical ridge lies to the north of Sydney this time of the year, it will bring westerly winds from the interior that produce mostly sunny conditions,^[26][22] at times warm, with the temperatures averaging between 21 and 25 °C (70 and 77 °F) with relatively low dewpoints, hovering between 4 and 12 °C (39 and 54 °F). Some days may be windy due to the dry westerlies and nights may be relatively cool, where temperatures plummet down to around 7 °C (45 °F) in some suburbs. Hot air from the interior that soars temperatures to over 35 °C (95 °F) can be expected, especially in the months of October and November. These conditions are rare in September, but not unheard of.^[53]

Extreme, changeable and inconsistent temperatures are much more prevalent in spring than other seasons. On some occasions, hot dry days are cooled down by a southerly buster, which eventually lowers the temperatures from 40 °C (104 °F) to as low as 19 °C (66 °F).^[61] Such extremes usually happen in mid-to-late spring. Other seasons seldom see such fluctuations in a day's span. Furthermore, the diurnal range is higher in this season than it is in autumn.^[12]

The lowest maximum temperature in spring was 9.5 °C (49.1 °F), recorded on 8 September 1869.^[12] 9am relative humidity is the lowest in the year during spring, ranging from 58% to 68%, with early spring receiving lower figures.^[40]

The highest maximum Spring temperature ever recorded at Sydney Airport was on 25 November 1982, when the temperature eclipsed at 43.4 °C (110.1 °F).^[62]

Though the highest Spring temperature recorded in Sydneys Metropolitan area was recorded at Richmond on 23 November 2014, peaking at 45.3 °C (113.5 °F).^[63]

D'harawal seasons

The Sydney Basin is in the traditional lands of the Dharawal people. The Dharawal describe six seasons for their country which extends from the southern shores of Port Jackson (Sydney Harbour) to the northern shores of the Shoalhaven River, and from the eastern shores of the Wollondilly River system to the eastern seaboard.^[64]

• January–March (Burran): Hot and dry
• April–June (Marrai'gang): Wet, becoming cooler
• June–July (Burrugin): Cold, frosty, short days
• July–August (Wiritjiribin): Cold and windy
• September–October (Ngoonungi): Cool, getting warmer
• November–December (Parra'dowee): Warm and wet

Warm and cool periods

The Bureau of Meteorology reported in 2011 that 2002 to 2005 had been the warmest years in Sydney since records began in 1859. 2004 saw an average daily maximum temperature of 23.4 °C (74.1 °F), 2005 of 23.4 °C (74.1 °F), 2002 of 22.9 °C (73.2 °F), and 2003 of 22.7 °C (72.9 °F). The average daily maximum between 1859 and 2004 was 21.6 °C (70.9 °F). Seven (of the ten) warmest years in 151 years of recordkeeping have occurred in the ten years between 2001 and 2010, with this decade being the warmest on record for minimum temperatures.^[65][66]

The Bureau of Meteorology reported that the summer of 2007–08 was the coolest in 11 years, the wettest in six years, the cloudiest in 16 years, and one of only three summers in recorded history to lack a maximum temperature above 31 °C (88 °F).^[67] The Bureau of Meteorology reported that 2009 was a warm year. The average annual daytime temperature at Observatory Hill was 22.9 °C (73.2 °F), which is 0.9 °C (1.6 °F) above the historical annual average. This ranks as the seventh highest annual average maximum temperature since records commenced in 1859.^[68] 2010 was the equal fourth warmest year on record for Sydney, with an average maximum of 22.6 °C (72.7 °F), which was 0.6 °C (1.1 °F) above the historical annual average.

Climate models in 2014 suggested that sea temperatures off Sydney are decades away from becoming "tropical". A scenario of increasing CO2 emissions proposed winter sea surface temperatures will consistently exceed 18 °C (64 °F) between 2020 and 2030, and summer sea surface temperatures will consistently surpass 25 °C (77 °F) between 2040 and 2060.^[69]

July 2017 to June 2018 in southeastern Australia proved to be the hottest financial year on record with maximum temperatures being the warmest on record and minimums above average.^[70] The warmest year on record was 2016, with a mean temperature of 19.6 °C (67.3 °F) degrees.^[71] Sydney's 2017 mean temperature of 19.5 °C (67.1 °F) degrees was 1.7 °C (3.1 °F) degrees above the long term average and the second highest value in 158 years of records. The 2020-21 summer was the coolest in a decade due to La Nina's influence.^[72]

Microclimate

Streets with tree canopy, which are usually found in the inner West and northern Sydney, tend to have lower air temperatures (Summer Hill).^[73]

Streets with lower tree cover, usually found in recent suburbs in the west, experience hotter temperatures due to heat radiation (Plumpton).^[74]

The region of Sydney is subject to phenomena typical of a microclimate, namely in late spring and summer, where the western suburbs are hotter than the Sydney CBD by 6–10 °C (11–18 °F)^[75] due to urban sprawl exacerbating the urban heat island effect and less exposure to mitigating sea breezes which cool down Sydney's eastern edge and fail to move 9 km (5.6 mi) inland. The dramatic temperature difference between coastal and inland areas is caused by a combination of desert-warmed air from central Australia reaching the west, and as well as density of housing, lack of vegetation or open spaces, and the Blue Mountains which help trap the hot air.^[76][77]

When it is 25 °C (77 °F) at Bondi for instance, the temperature will be around 30 °C (86 °F) just west of the Sydney Harbour Bridge, around 35 °C (95 °F) near Parramatta and as much as 40 °C (104 °F) 40 km (25 mi) inland. Such extreme temperature differences in the Sydney metropolitan area usually occur in late spring when the western Pacific Ocean is still quite cool and the inland air is warm.^[78] Furthermore, within the CBD, heat maps show the area around Central Station (in Haymarket) is 0.5–1.0 °C (1–2 °F) warmer than Circular Quay and surrounds, making it the hottest place in the CBD.^[79]

According to ecologist Sebastian Pfautsch from the University of Freiburg, in Sydney's hot days there could be discrepancies of up to 22 more days above 40 °C (104 °F) recorded in urban space compared to a weather station from the Bureau of Meteorology.^[80] Because 48.9 °C (120.0 °F) was recorded in Penrith (on 4 January 2020), it will nott be unusual to have a 50 °C (122 °F) reading somewhere nearby, especially if it lacked green space and retained heat to intensify heatwave temperatures.^[76] Richmond has the second largest overall temperature range recorded in Australia, after Mitchell, Queensland; −8.3 to 47.8 °C (17.1 to 118.0 °F).^[81][82]

Urban heat island

A study by the University of Western Australia and RMIT indicated that the western suburbs have a much stronger urban heat island effect than those east of the CBD and that hotter temperatures in the west are human contributed due to solar radiation absorbing materials in black asphalt and dark roofs, anthropogenic heat from cars and less natural environments, thereby creating a "heat dome" that blocks the cooler air from the sea. Greening Australia stated that January mean maximum temperatures in the west have risen at a pace of 0.65 °C per decade, over twice as much as eastern Sydney's 0.28 °C per decade.^[83] The OEH warned that further development could cause more exceedingly hot days in the west by 2030.^[77]

Urban heat island of the CBD has been efficaciously blocking the cooler air from reaching the inland suburbs because the CBD's "high temperature, is like a wall that stops the sea breeze in its tracks. Over Sydney’s CBD is a heat dome because of the high density of concrete and asphalt. If we want to cool western Sydney and demolish this wall, we need to cool the CBD first", Professor Mattheos Santamouris from UNSW states. He explained that cooling the CBD would reduce the temperature by 1.5 °C in the west and tree coverage could cool down suburban streets by as much as 10 °C (18 °F) in hot days since high-density housing developments and scarce trees trap heat.^[79][84] Waterbodies and open spaces also provide cooling benefits in urban areas.^[74]

According to climate researchers, relatively easy modifications such as constructing fountains and water playgrounds could also lower temperatures in the western suburbs. The city now has 3.6% more trees in 2016 than it did in 2009 and Penrith City Council had planned to plant 100,000 trees from August 2018, in addition to planning a large city park, creating a water-sensitive urban design, street shading, and the use of cool materials in its building developments.^[85] Furthermore, Parramatta City Council has installed 20 temperature sensors among different tree species in its suburbs to compare how different species can help reduce urban heat.^[86][87]

Precipitation

Rainfall seasonality

Rainfall is slightly higher or dominant during the first half of the year, particularly in late summer and early autumn, when the ocean has peaked its warmth.^[88] At this time of the year, the subtropical ridge is to the south of the continent, thereby directing easterly winds towards the east coast.^[c] Rainfall will tend to be lower in the second half of the year when the subtropical ridge is just to the north of the city where it picks up dry winds from the continent's interior towards Sydney (as it rotates counter-clockwise) and this will be when clockwise-rotating low pressure systems are to the south of the continent.^[22][89][90]

Due to the unpredictability of rain, the wettest and driest months change on a yearly basis. The "wet" and "dry season" is more pronounced in the inland suburbs with late winter to early spring (July–September) having a drying trend and late summer to early autumn being wetter and greener (February–March), making the region more close to the humid subtropical subtype Cwa.^[91] The drier winters are due to its rain shadow position on the leeward (eastern) side of the Great Dividing Range, which shield the region from south-westerly cold fronts that arrive from the Southern Ocean.^[92][93]

The annual evaporation rate for Sydney is 1,600 mm (62.99 in),^[94] with the rate in the summer being 600 mm (23.62 in)^[95] and in winter 300 mm (11.81 in).^[96]

Rainfall amount

Within the city and surrounds, rainfall varies, from around 675 mm (26.57 in) at Badgerys Creek^[97] (in the west) to 1,400 mm (55.12 in) at Turramurra (the northeast) in the Northern Suburbs, which create an orographic rainfall.^[98] Even in its months of highest rainfall, Sydney has relatively few rainy days, with an average mean of 7 to 8 rainy days per month on the 1 mm (0.04 in) threshold, despite having a moderate to high amount of annual rainfall at around 800 mm (31.50 in) to 1,100 mm (43.31 in) (depending on the area) – This illustrates that Sydney generally receives short-lived, heavy rainfall day events, usually not lasting more than 2 or 3 days, which give away to mostly propitious conditions for many weeks to months even, especially during an El Niño period (though during a La Niña event, rainfall may be intermittent for many days or weeks).^[99]

In 2011, Sydney recorded its wettest July since 1950. The CBD recorded 244 mm (9.61 in) of rain that month. 2011 was also the wettest year since records began in 1858.^[100] In 2022, Sydney recorded its wettest March on record with the rain gauge picking up 554 mm (21.81 in) of rain, beating 521.4 mm (20.53 in) from 1942 – this also brought Sydney's annual total up to 1,076.2 mm (42.37 in), which is the highest January-to-March total in records that date back to 1859. The high amount of rainfall was caused by a combination of the La Nina phase, an anomalously warm Tasman Sea, and a consistently positive Southern Annular Mode (SAM).^[101][102] In April that year, Sydney CBD exceeded its long-term annual average rainfall of 1,226.8 mm (48.30 in), which set a new record for the fastest time to accumulate a year's worth of rain in the CBD. This surpassed the previous record by a month – The old record was 3 May in 1990 and the following record was 6 May in 1890.^[103] Sydney also recorded its wettest July on record that year where 404 mm (15.91 in) of rain fell during the month, surpassing the July 1950 record.^[104] 2022 ultimately recorded 2,530 mm (99.61 in) of rainfall, the wettest year on record, surpassing the previous record of 2,194 mm (86.38 in) in 1950.^[105]

Storms

East coast lows, which strike from the southeast in the Tasman Sea, provide heavy rainfall typically in autumn to early winter with Sydney CBD being greatly impacted due to its location on the coast. They can make landfall at any time of the year, typically usually during a positive SAM phase.^[106] The precipitation of the low comes from a nimbostratus cloud that dumps as much as 70 mm (2.76 in) of rain for as much as two days, though when the cloud is thick enough 100 mm (3.9 in) of rain can fall in three hours as was the rare case in August 1986.^[107] Other rainfall drivers include Black nor'easters (in the warm months), upper-level lows (all year round), Australian northwest cloudbands (autumn-spring) and as well as, albeit rarely, tropical cyclone remnants (warm months) and cut-off lows (cool months).^{[citation needed]}

Due to onshore winds, the CBD is susceptible to some light rain and drizzle – These conditions usually do not penetrate the inland suburbs. However, the western suburbs are more inclined to receive thunderstorms in summer due to the stabilizing effect of a sea breeze in the afternoon near the CBD and Eastern Suburbs, however the stabilizing effect does not always occur as was the case during the 1947 event as according to Newmans report there was a sea breeze on the day it occurred.^[108]

On some days, rain may come in drizzle form, though this is rare as most rain comes mostly from major storms. In the warm months, isolated convective showers form when a cold pool arrives from the southwest, particularly on hot and sultry days.^[109] These showers usually come in heavy downpours and can include hail, squalls, and drops in temperature whereby offering some respite, but they generally pass very quickly with a clearing trend to sunny and relatively calm weather.^[110] Black nor'easters may provide persistent rainfall for a few consecutive days.^{[111][12][40]}

The city is rarely affected by cyclones, although remnants of ex-cyclones do affect the city.^[112] The city is prone to severe hail storms, such as the 1947 Sydney hailstorm, wind storms, and flash flooding from rain caused either by East Coast Lows (such as the major storm in early June 2007) or ex-tropical cyclone remnants. Scientists have predicted that rainfall will become more unpredictable and temperatures will be on the rise.^[113][114] Parts of western Sydney were substantially flooded during the New South Wales 2021 floods, with many areas around Richmond and Windsor submerged in floodwaters.^[115] In early 2022, Sydney recorded its wettest start to a year on record with the running annual total being 821.6 mm (32.35 in), topping 782.8 mm (30.82 in) to the same date in 1956 and 753.8 mm (29.68 in) in 1990, respectively (rainfall data at Sydney Observatory Hill dates back to 1858).^[116]

Snowfall

Snow is extremely rare in Sydney, with significant snowfall being last reported in the Sydney area on 28 June 1836. On that date, it was reported that convicts and British settlers in Hyde Park woke up to snow "nearly 1 in (25.40 mm) deep", with the meteorological table in The Sydney Herald recording that on the morning of the snow the temperature dropped to 3 °C (37 °F). The snow event affected trading where sellers were unable to transport goods to markets in the colony. The snowfall occurred at the end of the dalton minimum, a solar cycle period representing low solar activity, where colder temperatures were recorded globally.^[117] A keeper of weather observations during that period, T. A. Browne noted:^[118]

The years 1836, 1837 and 1838 were years of drought, and in one of these years (1836) a remarkable thing happened. There was a fall of snow; we made snowballs at Enmore and enjoyed the usual schoolboy amusements therewith.

The Sydney Morning Herald reported on the event, saying:

For the first time in the memory of the oldest inhabitants, snow fell in Sydney on the morning of Tuesday last. 27 June 1836, about 7 o'clock in the morning, a drifting fall covered the streets nearly one inch in depth...A razor-keen wind from the west blew pretty strongly at the time and altogether, it was the most English like winter morning ever experienced.

The Sydney Monitor reported:^[119]

We believe snow was never seen in Sydney before the previous night. The weather was cold, but not more so than we have often felt it before.

Scant snowfall has been recorded in latter dates:

• On 22 June 1951, light snowflakes (which melted into rain) were reported in the suburbs of Liverpool, Pymble and Kingsgrove.^[120]
• On 18 July 1965, very light snow fell in Berowra Heights and Hornsby.^[121]
• On 21 June 1972, settling snow was allegedly observed in what is now Kellyville Ridge, although it may have been soft hail or ice pellets.^[122]
• On 25 July 1986, melting snow was observed in metropolitan Sydney, in addition to some settling snow being reported in North Ryde.^[123][124] Moreover, snow flurries were observed in the northern suburbs that day, which melted in several minutes, although there was no record of any snow in Sydney CBD.^[125]
• On 27 July 2008, a fall of graupel or soft hail (which was mistaken for snow by residents), blanketed Lindfield, Roseville and Killara in white. Owing to this event, a senior forecaster from the Bureau of Meteorology doubted the 1836 snow account, stating that weather observers in that time period lacked the technology and skill to distinguish snow from soft hail.^[126]

Blue Mountains

The Blue Mountains, a temperate oceanic region bordering on Sydney's metropolitan area, have a reputation for snow in winter, with places such as Katoomba, Leura and Blackheath receiving the most snow due to their higher elevation. Despite the reputation, there are only around five snowy days per year in the upper mountains area with two settled falls per season, and another five to ten days of light snow showers or sleet. Settled snow has become less common in recent decades.^[127] It is extremely rare to see snow below Lawson.^[128]

Drought

Sydney's climate appears to be becoming drier; The city has had fewer rain days in recent years than shown in the long-term climate table above. In summer, Sydney can go for long periods without rainfall. The other phenomenon that arises from these long, dry and hot periods is bushfires, which occur frequently in the areas surrounding the city. Water supply is a recurring concern for the city during drought periods.

In 2005 the reservoirs reached an all-time low. Many areas of the city bordering bushland have experienced bushfires, notably in 1994 and 2001–02 — these tend to occur during the spring and summer. Heatwaves, which are regularly occurring in recent years, usually lead to water restrictions and a high risk of bushfires, which sometimes bring a smoky haze to the city. Smog is noticeable on hot days, even without bushfires.^{[129][130][131]} The years 2009 and 2010 had dry conditions, according to Bureau of Meteorology.^[132]

In September 2013, the combination of dry weather, warm temperatures and strong winds brought early-season bushfires. The summer of 2013-14 was the driest in 72 years. The widespread bushfires in December 2019 affected the western periphery of the city, and the Sydney metropolitan area suffered from dangerous smoky haze for several days throughout the month^{[133][134][135][136]} 2019 was one of Sydney's warmest in 161 years and the driest since 2005, which had a few days of raised dust and as well as declining dam levels.

Wind

Afternoon windspeed recorded in Sydney Airport averages at 24.3 km/h (15.0 mph) in an annual basis, making Sydney the windiest capital city in Australia.^[137] As a whole, the Sydney region is generally the windiest from October to January and calmest from March to June. The windier locations are those by the coast, such as the eastern suburbs. The prevailing wind annually is northeasterly. In the warm months, only 40% of the time Sydney gets wind directions from the northwest or southwest, which are the dry winds flown from the heated interior of Australia.^[138]

Northeasterlies and easterly sea breezes are dominant from early summer to early autumn, because the anticlockwise-rotating subtropical ridge is to the south of the city where it allows winds from the sea to penetrate. Westerlies are dominant in late winter to mid-spring as the subtropical ridge is just to the north of the city, picking up winds from the interior and blocking easterlies from the sea.^[22] Westerly winds in Sydney are intensified when the Roaring forties contract towards the southeastern Australia.^[139]

Southerly busters are expected from October to the end of March. They typically look like as if a sheet of cloud is rolled up like a scroll by the advancing wind. The change of wind (in the warm months) is sometimes very sudden, where it may be fresh northeasterly and in ten minutes a southerly gale. Katabatic winds are light, south-westerly drainage winds, akin to land breezes, that occur when air of higher density in the Blue Mountains descends under gravity force into the Sydney metropolitan area and the Hawkesbury Basin, usually during a winter night.^{[140][141][142]}

Air masses

Sydney is affected by five air mass types throughout the year:^[143]

• Tropical continental (CT): Very hot, dry air from northern half of central Australia that can bring extreme heat, typically from late spring to summer (i.e. brickfielder). These come from the northwest and are called north-westerlies.
• Tropical maritime Tasman (MT): Mild to warm, moist airmass from the northern Tasman Sea that brings overcast, humid, sometimes showery conditions and even heavy rain at any time of the year (i.e. east coast lows, black nor'easters). These are north-easterlies or northerlies.
• Subtropical continental (ST): Mild to warm, dry air from southern central Australia that is more dominant in late winter to early spring (i.e. the Australian High). These are westerlies.
• Southern maritime (SM): Mild to cool, moist air from the Southern Ocean that brings drizzle and, at times, cloud cover at any time of the year (i.e. southerly busters). These are southerlies or south-easterlies.
• Modified polar maritime (MP): Cool, sometimes cold, generally dry airmass, typically occurring in winter (though not unknown in late autumn and early spring), that can be very windy when it arrives from the southwest over the Great Dividing Ranges (i.e. southeast Australian foehn).^[d] These are south-westerlies.

Föhn effect

Since Sydney is located on the Great Dividing Range's eastern side, and is thus in its rain shadow,^[e] it experiences a föhn-like type of wind, particularly between late autumn and spring, which is a dry south-westerly that raises the air temperature and provides clear to partly cloudy conditions in the lee of the mountains (in this case, the Sydney Basin). During the phenomena, atmospheric moisture is reduced due to the partial orographic obstruction of comparatively damp low-level air and the subsiding of drier upper-level air in leeward of the mountains.^[144][4]

In the cool season, these föhn-like winds can be particularly damaging to homes and affect flights, in addition to being uncomfortable, as the wind chill factor usually makes the temperatures feel cooler than what they are.^[145][146]

Conversely, the foehn effect is one the few reasons why Sydney and other places in the coastal plain register high temperatures in the warm season but seldom attain cold maximum temperatures in the winter,^[147] and also the reason why late winter and early spring have the most clear days in the year, as the Great Dividing Range shelters the region from vigorous westerly cold fronts that arrive from the Southern Ocean.^[148][149]

Historical descriptions

In 1819, British explorer William Wentworth described Sydney's climate as:^[150]

Highly salubrious and delightful, although the heats in summer are sometimes excessive, the thermometer frequently rising in the shade to 90 °F (32 °C), and even to a 100 °F (38 °C) and upwards of Fahrenheit – This, it must be admitted, is a degree of heat that would be highly oppressive to Europeans, were it not that the sea breeze sets in regularly about nine o'clock in the morning. If the summers are occasionally a little too hot for the European constitution, it will be remembered that the extreme heats which I have noticed as happening during the north-west winds, are of but short continuance; and that the sea and land breezes, which prevail at this season in an almost uninterrupted succession, moderate the temperature so effectually, that even new comers are but little incommoded by it. The hot season, however, which is undoubtedly the most unhealthy part of the year, does not, as will have been perceived, continue above four months. The remaining eight possess a temperature so highly moderate and congenial to the human constitution, that the climate of this colony would upon the whole, appear to justify the glowing enthusiasm of those who have ventured to call it the Montpellier of the world.

Below, Wentworth describes Sydney's^[f] seasonal and annual weather patterns in analytical detail:^[150]

Summer

During these three months violent storms of thunder and lightning are very frequent, and the heavy falls of rain which take place on these occasions, tend considerably to refresh the country, of which the verdure in all but low moist situations entirely disappears. At this season the most unpleasant part of the day is the interval which elapses between the cessation of the land breeze and the setting in of the sea. This happens generally between six and eight o'clock in the morning, when the thermometer is upon an average at about 72 °F (22 °C). During this interval the sea is as smooth as glass, and not a zephyr is found to disport even among the topmost boughs of the loftiest trees.

Autumn

The weather in March is generally very unsettled. This month, in fact, may be considered the rainy season, and has been more fertile in floods than any other of the year. The thermometer varies during the day about 12 °C, being at day-light as low as from 55 to 60 °F (13 to 16 °C), and at noon as high as from 70 to 75 °F (21 to 24 °C). The sea and land breezes at this time become very feeble, although they occasionally prevail during the whole year. The usual winds from the end of March to the beginning of September, are from S. to S. W.

The weather in the commencement of April is frequently showery, but towards the middle it gradually becomes more settled, and towards the conclusion perfectly clear and serene. The thermometer at the beginning of the month varies from 72 to 74 °F (22 to 23 °C) at noon, and from the middle to the end gradually declines to 66 °F (19 °C) and sometimes to 60 °F (16 °C). In the mornings it is as low as 52 °F (11 °C), and fires become in consequence general throughout the colony.

The weather in the month of May is truly delightful. The atmosphere is perfectly cloudless, and the mornings and evenings become with the advance of the month more chilly, and render a good fire a highly comfortable and cheering guest. Even during the middle of the day the most violent exercise may be taken without inconvenience. The thermometer at sun-rise is under 50 °F (10 °C), and seldom above 60 °F (16 °C) at noon.

Winter

The three winter months are June, July, and August. During this interval the mornings and evenings are very chilly, and the nights excessively cold. Hoar frosts are frequent, and become more severe the further you advance into the interior. Ice 0.5 inches (1.3 cm) thick is found at the distance of 20 mi (32 km) from the coast. Very little rain falls at this season, but the dews are very heavy when it does not freeze, and tend considerably to preserve the young crops from the effects of drought. Fogs too are frequent and dense in low damp situations, and on the banks of the rivers. The mean temperature at day-light is from 40 to 45 °F (4 to 7 °C), and at noon from 55 to 60 °F (13 to 16 °C).

Spring

The spring months are September, October, and November. In the beginning of September the fogs still continue; the nights are cold, but the days clear and pleasant. Towards the close of this month the cold begins very sensibly to moderate. Light showers occasionally prevail, accompanied with thunder and lightning. The thermometer at the beginning of the month is seldom above 60 °F (16 °C) at noon, but towards the end frequently rises to 70 °F (21 °C)

In October there are also occasional showers, but the weather upon the whole is clear and pleasant. The days gradually become warmer, and the blighting north-west winds are to be apprehended. The sea and land breezes again resume their full sway. The thermometer at sun-rise varies from 60 to 65 °F (16 to 18 °C), and at noon is frequently up to 80 °F (27 °C).

In November the weather may be again called hot. Dry parching winds prevail as the month advances, and squalls of thunder and lightning with rain or hail. The thermometer at day-light is seldom under 65 °F (18 °C), and frequently at noon rises to 80 °F (27 °C), 84 °F (29 °C), and even 90 °F (32 °C).
— William Wentworth, Statistical, Historical, and Political Description of NSW

In the February 1938 issue of The Home, journalist Basil Burdett wrote, "...Even Melbourne seems like some grey and stately city of Northern Europe compared with Sydney's sub-tropical splendours."^[151]

Classifications

Climate data

^{[note a]}

^[note a] : The Observatory Hill weather station covers the climate for Sydney CBD, the City of Sydney's northern portion and as well as the harbourside eastern suburbs and the Lower North Shore suburbs which lie on Port Jackson. The suburbs in the southern parts of the City of Sydney or the Inner City region are more adjacent to Sydney Airport's climate station.

Miscellaneous data

See also

• Climate of Australia
• Geography of Sydney
• Environment of Australia
• Australian region tropical cyclone
• Climate change in Australia
• Effects of global warming on Australia
• Effects of the El Niño–Southern Oscillation in Australia
• Severe weather events in Sydney

Notes

References

External links

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