Weather is a major element in safety at sea. An accurate forecast can inform seafarers and help them to plan their route or even decide whether they will set out or not.
The weather at Mizen Head is a classic alternation of low and high-pressure systems (depressions and anticyclones). The prevailing wind is from the northwest. Mizen Head, the most southwesterly point of Ireland, is projecting out into the Atlantic Ocean where the currents bring the warm waters of the tropics past in the Gulf Stream. The tides around Ireland and the Atlantic Ocean meet in a turbulent swirl. It is only possible to land onto the Fastnet Rock directly from a boat approximately twelve times in the year. Mid-Atlantic storms send huge waves to crash on the cliffs at Mizen.
Until recently the only way to predict the weather accurately was to rely on people collecting up to the minute data about the weather in their area. They passed it on to a central office where it was collated and analysed.
Lightkeepers had an important role in the collection of weather data. As a part of their daily routine they collected information about the weather for the Irish Lights. At regular intervals during the day they collected measurements and recorded them in ledgers. This information was not passed on daily. The information they collected was air temperature, barometric pressure, sea state, visibility, wind force and direction, Beaufort Weather Notation (Present weather).
As you see on the board, it was quite a complicated procedure.
There were nine readings to report.
Table I (1) N Amount of Sky Covered
Table II (2) DD Wind Direction
Table III (3) ff Wind Speed
Table IV (4) VV Visibility
Table V (5) ww Present Weather
Table VI (6) W Past Weather (in the last 6 hours)
Table VII (7) State of Sea
TT Air Temperature
PPP Atmospheric pressure
Each of these tables had a different code. It was much easier for a Lightkeeper to say to the weather office ‘N8’ than to say ‘the sky is completely overcast’.
The code at the top of the Board gives the order in which readings were given at Mizen Head
MMDDHHHH (MIZEN HEAD) Nddff (Tables I, II, III) VVwwW (Tables IV, V, VI) PPPTT (Atmospheric pressure, Air Temperature) Sea State (Table VII) MINVIS/…
So see if you can interpret this weather reading using the Board (in a file at the end of this page).
Coded weather reading:
N = 5
DD = 27
ff = 6
The coded weather data means:
The sky is five eighths covered with cloud
The wind is from the west
The wind is a strong breeze blowing at 22 – 27 knots
The visibility is 6 miles
There are moderate to heavy rain showers
In the last six hours it was raining
TT The air temperature is ten degrees Celsius
PPP The atmospheric pressure is 992 millibars (low)
The Sea State is rough with the height of the waves 2.5 – 4 metres in height.
The Lightkeepers had to take these readings at set times every day – 6am., 11 am., 2pm., 4pm., 6pm. and 10pm.
With the development of satellites, weather data collection has been automated. A computer can collect data constantly and quickly. Mizen Head Signal Station has been automated since 1993 and when the Lightkeepers left the collection of weather information ceased. There has been no weather data collection here since.
In 2001 the MILOS Automatic Weather Station was installed at Mizen Head and it was hoped that Met Éireann would access the readings by modem. However, because the cliffs distort the wind speed, Met Éireann required a hard wired anemometer fixed on a plateau 600 m from the centre. This was not feasible, so the idea was abandoned. Also, it proved impossible to get broadband at Mizen Head as it is out of range of all but a satellite connection. The satellite connection had a slight delay, which proved difficult for any automatic transference of data.
This weather station was completely stripped of some of its equipment in a bad winter storm. It was repaired and went back into service collecting the daily information onto a hard disk. The next winter another bad storm with winds up to 130mph completely stripped all the equipment from the MILOS Automatic Weather Station (AWS). It was not replaced.
In the last 5 years, weather stations have been transformed by IT. They are now much smaller. In 2019 two new AWS displays were created – one in Mizen Hall and one over the Bridge in the Keepers’ Quarters. Visitors are invited to take weather readings as the Keepers did. All the charts are there to help to write an accurate weather report.
Present Weather Monitor
The MILOS 520 System Automatic Weather Station was on a mast on the way down to the Signal Station.
On the mast there was:
An anemometer to read wind speed.
A wind vane to read direction
A digital barometer
A humidity and temperature probe
A rain gauge
A ground temperature sensor
In the Mizen Hall the present weather was displayed on a monitor. It showed measurements of various elements of the weather in the last 24 hours.
Air Temperature – how warm or cold it is
Humidity - how much moisture is in the air
Dewpoint Temperature - the temperature to which the air must be cooled for condensation to occur (for fog to form)
Pressure – to show low or high pressure
Precipitation – rain, sleet, and snow
Climatic data are available for Roaringwater Bay, as Sherkin Island Marine Station has maintained meteorological records since July 1972. The area has a mild, moist, Atlantic climate, with strong winds, especially during winter months. There are few frosts, and snow is almost unknown, at least at sea level. Rainfall is high, fed for much of the year by low-pressure weather systems over the Atlantic, and dry spells (at least 15 days with less than 1.0 mm of rain) are infrequent. Absolute drought (at least 15 days with less than 0.2 mm of rain) does occur, but never for more than a month at a time (Palmer 1986). Nevertheless, the wind and relatively high sunshine levels have a drying effect on the landscape and vegetation. During the summer months, rocky ground and south-facing slopes dry out, creating the conditions favoured by plants of more southern affinity.
The rain, as in much of Ireland, is not generally heavy but consists of falls of low intensity over extended periods -the 'soft' weather of country people. Annual rainfall recorded on Sherkin ranges from 910.0 mm (1975) to 1392.4 mm (1982), with an average of 1124.8 mm over the years 1972-84. December is the wettest month, with an average rainfall of 136.8 mm; April, with an average of 45.8 mm, is the driest month (Palmer 1986). During the last decade this pattern of wet and dry months has become more erratic. The high rainfall and frequent mists are favourable to plant growth. It has been said that the weather in western Ireland consists of gales interspersed with windy periods. The worst winds come during the winter months, but summer gales are frequent and can do considerable damage to plants. The flowers and fruits of plants, especially on exposed coasts, are often brown and withered after a period of salt-laden Atlantic winds.
The Atlantic Ocean, together with warm currents derived from the North Atlantic Drift, has a moderating effect on the temperature of coastal areas such as Roaringwater Bay, creating few extremes of climate in either winter or summer. During the period 1975-84 the average air temperature in January and February, the coldest months, was 6.7°C; the average temperature in August, the warmest month, was 15.5°C (Palmer 1995b). Between 1975 and 1994, rarely did the air temperatures fall to 0°C on more than 10 days a year. The last 10 years have seen far fewer frosts (for example, no air frost at all was recorded in 1989), whereas in 1978 and 1979 there were 22 and 26 days of air frost respectively. During the last 20 years, the temperature rarely fell below -4°C, although -7.7°C was recorded in January 1979. Conversely, the temperature in summer rarely rose above 20°C, although 26.4°C was recorded during the famous hot August of 1976.
Sunshine levels in Roaringwater Bay are high -coastal areas usually receive greater amounts of sunshine than those inland. May is by far the sunniest month, but high levels of daily sunshine may be enjoyed from early April through to the end of August (Palmer 1995a). During the last 10 years at least, May has been a particularly sunny and dry month.
Source: The Wild Plants of Sherkin, Cape Clear and adjacent Islands of West Cork. Ed. John Akeroyd. Sherkin Island Marine Station, Sherkin Island, West Cork, 1996.