Macquarie Island - Climate - Bureau of Meteorology

Climate of Macquarie Island

Overview

The characteristic features of Macquarie Island's climate are the small variation in temperature both seasonally (through the year) and diurnally (through the day), and the persistent strong prevailing west to northwesterly winds.

The weather is also marked by overcast skies and a large number of days with precipitation. Low temperatures, strong wind and precipitation combined to make wind chill a major hazard for people living on the Island. There is no permanent snow cover but in most years the upper levels of the plateau are covered with wet snow much of the time.

The milder months are from December to March, while the colder months are from June to August. Rainfall is highest in March and April, but not greatly so. Strong winds are least common in December and January.

K.C. Hines (who participated in the first ANARE in 1948) described the Island's weather:

For days on end the upper plateau would be shrouded in mist and a great wall of fog would block out the sea on all sides. A fine misty rain would be falling continuously and the inevitable wind sweeping in past the apparently impenetrable fog barrier.

Temperature

Mean daily maximum temperatures range between 8.8 °C in January and 4.9 °C in July. Mean daily minima range from 5.3 °C in January and February to 1.5 °C in June. The highest temperature on record is 14.4 °C (in December 1984), the lowest on record is -9.4 °C (in July 2003).

The mean daily temperature range (the difference between the minimum and maximum temperature recorded each day) is 3.5 °C, and is relatively constant through the year. This small range is typical of oceanic islands at these southern latitudes and is very similar to those recorded at Campbell Island, Kerguelen Island, Marion Island and the Falkland Islands.

Temperatures below 0 °C have been recorded in every month except January. About one day in five from June to September has a minimum temperature below zero, but only about 1 day in 100 is the minimum colder than -4°C. On only about 1 day in 100 does the temperature exceed 10 °C.

Wind

Macquarie Island lies in the regime of the mid-latitude westerlies, known colloquially as the "Furious Fifties". Over two-thirds of winds are from a direction between west and northwest. The mean wind speed is about 30 km/h. March to May and again from August to October are the windiest parts of the year, when the north-south pressure gradient is strongest. Wind gusts in excess of 80 km/h occur on over one-third of the days in these months. The strongest wind gust recorded is 185 km/h, and gusts over 140 km/h have been measured in all months. December and January are the least windy months, but even then the average wind speed is about 27 km/h.

The station winds are not always representative of the winds on other parts of Macquarie Island. In strong southwesterlies, for example, the station often reports lower wind speeds than elsewhere around the Island. The elongated ridge of the Island intercepts the wind flow from all directions and this results in local "lee vortices" particularly in the region of the observing station at Buckles Bay. Here the topographic effects of the detached peak of Wireless Hill, the low lying isthmus and the northern end of the main ridge result in variable lee wind patterns in the prevailing westerly flow. This often causes difficult conditions during ship-to-shore operations.

The persistent strong winds can lead to rapid loss of body heat. This "wind chill" problem is a major concern for those visiting the Island, even though extremely cold temperatures are rare.

Humidity

Air rushing over the great expanse of ice-free, wind-swept sea that surrounds Macquarie Island picks up a great deal of moisture. As a result, the relative humidity on the Island is typically over 85 %, and is over 95 % about one-third of the time. The mean value of around 87 % is the highest for an Australian observing station.

Cloud, Mist and Fog

Macquarie Island is often cloudy, typical of a mid to high latitude maritime environment. On average, almost seven-eighths of the sky are covered by cloud. Days without any cloud are rare, and it is not uncommon for completely overcast skies to persist for days on end.

The Island is often obscured by fog or mist, with the upper parts of the plateau frequently being shrouded in low cloud for days on end, even when conditions on the isthmus are relatively cloud free. Prolonged periods of northerly air-flow, often due to slow moving highs over the Tasman Sea, bring moist warm air from lower latitudes causing vast areas of fog over the waters surrounding the Island. Fogs are also common in northerly air flow ahead of frontal changes. Fogs are observed at Macquarie Island on average about 65 days each year and are distributed fairly evenly in all months. Visibility in these fogs is often less than 50 metres, especially on the inland plateau.

Rain and Drizzle

Mean annual precipitation is 954 mm, and the median value is not much different at 958 mm. Autumn is slightly wetter than winter or spring, but all months receive rain. Heavy rain is quite rare, with only about 1 day in the average year receiving more than 25 mm. The wettest single day was in March 2001, with 52.8 mm. Such heavy rain has been known to trigger landslides on the Island.

The driest month on record was December 1959, with 16 mm, whilst the wettest was March 1988 with 181 mm. Measurable precipitation is recorded on an average of 313 days per year, or almost six days out of seven. This is fairly consistent across the year.

Snow and Hail

Snowfall can occur at any time of the year, happening on about 80 days on average at sea level. It is least likely in January (less than one day on average) and most likely in September (almost 8 days). A typical year would see up to half a dozen falls of around 10 cm depth at sea level. In most years the upper part of the plateau is covered in wet snow much of the time, particularly from May to October, with depths in level areas between one-half and one metre by the end of the season.

Hail, normally small in size, is also relatively common on the Island, occurring on about 65 days a year on average. It is most likely in October and least likely in January. Thunderstorms are rare but do occur, averaging about 1 per year at the station.

Last updated on 17 June 2004

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