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Weather and climate

Be prepared!

Don’t knock the weather. If it didn’t change once in a while, nine out of ten people couldn’t start a conversation.
Phil Armstrong in 2 Promises

St Helena was settled by the British, so of course we like to talk about the weather…

This page is in indexes: Island Nature, Island Detail

Clouds over the St Helena coastline Saint Helena Island Info Weather and climate

Below: SunWindRainSeasonsExpected weatherCurrent weatherIn more technical terms…Unexpected weatherRead More

All recent weather data recorded at the Meteorological Station.

In excellence of climate, St Helena is perhaps without an equal; no heat of torrid zones, or cold blasts from frigid regions, approach its genial shores. There no thunder-storms terrify the timid, no cholera, no yellow-fever, no small-pox, scarlatina, or deadly lurking fever-germs pollute the air. Nor is its balmy atmosphere ever marred by scorching winds, hot vapours, typhoons, hurricanes, cyclones, or any other characteristic of tropical regions. Throughout the year bright sunshine, clear skies, gentle breezes and deep blue seas, all combine to make it one of the most charming spots that can be found.{a}

More recently, according to the Wikipedia The climate of Saint Helena island can be described as tropical, marine and mild. Although basically correct our weather is far more complex than that. Here are the main features:

Sun

Sun Saint Helena Island Info Weather and climate

St Helena is in the Southern Hemisphere, north of the Tropic of Capricorn, which means the midday sun is directly overhead during the summer. The temperature can reach 34°C on a sunny day, though you won’t swelter due to the wind. More normal temperatures are in the range 20-27°C. The hottest months are between January and March and the cooolest are between June and September.

Tip: the tropical sun can be hot; sunscreen is recommended if going out for the day, especially on a boat{3}.

Wind

Wind Saint Helena Island Info Weather and climate

Wind direction Saint Helena Island Info Weather and climate
Wind direction{1}

Being within the range of the Southeasterly Trade Winds stops the weather from becoming uncomfortably hot and keeps the air fresh, even in the enclosed valleys such a Jamestown. Typical wind speeds are in the range 15-30Km/h. Wind speeds up to 80Km/h have been recorded but are very unusual. The lowest wind speed recorded in recent years was 17Km/h.

Rain

Rain Saint Helena Island Info Weather and climate

Surrounded by at least 1,900Km of ocean in any direction, you can expect a little rain. How much depends on the time of year, where you are and also, to a greater or lesser extent, on Sod’s Law{4}. That being said, the main wet periods are in March (the ‘Lent Rains’) and August (‘Scruffy August’{5}). Your location can be important - Jamestown receives less than 11cm of rainfall per year (only about 5% of the total across the rest of the island); the peaks can receive 102cm. And the weather is very variable; it can be raining in Longwood and sunny in Jamestown, and then an hour later the two can reverse. The good news is that a dull rainy morning can often lead onto a bright sunny afternoon.The highest monthly rainfall in recent years was in February 2011: 120.8mm.

The record rainfall in a 24-hour period is 48.6mm, recorded on 26th April 2017. On that day the typical rainfall for a month fell in just 6 hours!

Tip: bring a light waterproof, preferably one that packs down to fit in a pocket when not in use.

When it does rain it can be heavy!

Seasons

Seasons Saint Helena Island Info Weather and climate

In effect St Helena doesn’t have any. It gets hotter in January-May and cooler in August-October but the difference is not great (see Expected weather (below)). There is no Autumn (‘Fall’) so trees shed their leaves when they feel like it, and no Spring so things grow at any time of the year.

Tip: this means that there is no bad time of the year to come!

For countryside this green you have to expect a little rain Saint Helena Island Info Weather and climate
For countryside this green you have to expect a little rain…

If you like your information diagrammatically:

Weather chart Saint Helena Island Info Weather and climate

Expected weather

Here are the expected weather statistics for this and the next eleven months (based on recent history):

Figures, provided by the St Helena Meteorological Station, are monthly averages over the years 2001-2016, taken at Bottom Woods (North-west island temperatures - e.g. Jamestown or Half Tree Hollow - will be higher and rainfall lower). Figures in brackets [] are percentages of the annual total.

The data show a few interesting facts that do not accord with island folklore:

  • August is not the month with least sunshine. That honour is shared jointly by September and October.

  • August is also not the month with the most rainfall. It is (slightly) beaten by June and (surprisingly) March{6} - the ‘Lent Rains’.

  • The hottest month is neither January nor February. It is March, which is also the month with the most sun-hours{6}.

Current weather

There’s current time zone and weather information here or here and the site indexed below gives a general island view. You can also get information from BBC Weather.

Follow for a detailed forecast opens in a new window or tab links to WeatherUndergound.com/ Saint Helena Island Info Weather and climate

Our Meteorological Station

Our Meteorological Station opened on 1st September 1976, replacing an older station at Hutt’s Gate. It is located in Bottom Woods, 15.93°S 5.66°W, 436m above sea level.

It takes daily ground weather readings, and releases a daily weather baloon to measure upper atmospherre conditions:

At approx. 11:15 daily, the Weather Station launches a weather balloon with a small lightweight device known as a Radiosonde. As the balloon/radiosonde ascends, measurements of temperature and relative humidity are made at 2-second intervals.

A GPS receiver in the device allows its location to be identified from which the pressure, wind speed and direction can be calculated. Data is transmitted back to a ground receiver for encoding and onward distribution to the UK MET Office.

Typically when launched, the balloon rises at 5.5 m/s to reach a height of about 25km. As pressure decreases with height, the balloon expands until it bursts at which point the radiosonde device returns to Earth.

Where measurements are required at very high levels in the atmosphere, larger balloons like the ones used on St. Helena are capable of reaching 35km.{b}

The Meteorological Station at Bottom Woods Saint Helena Island Info Weather and climate
The Meteorological Station

In more technical terms…

The following comes from www.io-warnemuende.de/en_hix-st-helena-island-climate-index.html:

The Benguela upwelling system in the subtropical southeast Atlantic is subject to dramatic interannual fluctuations sometimes termed ‘Benguela Niño’ events. The South Atlantic Anticyclone (SAA) is assumed to be the responsible climatic ‘activity centre’ for the south-east trade winds driving the upwelling processes along the Namibian and South-west African coasts.

Air temperature and humidity signals of this region, modulated by upwelling-controlled sea surface temperature (SST), are carried by the trades towards St Helena Island. The island’s 1893-1999 century-long monthly weather Records of temperature, pressure and rainfall have been assembled and homogenized. They exhibit trends for decreasing precipitation (10mm/100yr), increasing air temperature (0.9°C/100yr), and decreasing air pressure (0.6hPa/100yr).

Their first empirical orthogonal eigenfunction (EOF) covers 46% of the total variance; its associated temporal coefficient is proposed as a ‘St Helena Island Climate Index (HIX)’. Austral winter HIX has a 42% correlation with a remotely sensed SST-derived Benguela upwelling index, called IBU, for the time period 1982-1999.

Not yet identified Benguela Niños (1895, 1905, 1912, 1916, 1946) and years of strong Benguela upwelling (1911, 1922, 1967, 1976) are newly suggested by the HIX.{7}

Unexpected weather

As with weather elsewhere, conditions sometimes exceed normal expectations…

Below: Things we don’t getThunder & Lightning’Rollers’The aliens are coming!It never rains…Hypothermia. On St Helena?

Things we don’t get

Hurricanes, typhoons, tornados & dust storms

Wind speeds up to 80Km/h have been recorded but are very unusual.

Earthquakes

They get them on Ascension Island, because they are right on the Mid-Atlantic Ridge, but we are further away and only get occasional minor tremors.

Frost, snow, hail & ice storms

G. C. Kitching claims the lowest temperature ever recorded on St Helena was 46°F in 1898; more recent records show a minimum of 18.6°C. G. C. Kitching also claims hail did once fall on St Helena, at Woodlands in a storm on 21st October 1897.

Heatwaves

G. C. Kitching claims an absolute maximum of 87°F was recorded at Woodlands in 1893; more recent records show a maximum of 27.5°C.

Droughts

We did have a significant water shortage in 2013 - the first for more than a decade - and another in the summer of 2016/17, but in neither case were drinking water supplies in danger so you couldn’t call either a drought by any means.

Monsoons

The highest monthly rainfall in recent years was in February 2011: 120.8mm.

Volcanic eruptions

The last eruption was between 10 and 7 million years ago, forming part of the island. We are told we should not expect any more…!

We rarely get thunderstorms.

Snow in Blue Hill? No just clever photo editing! Saint Helena Island Info Weather and climate
Snow in Blue Hill? No, just clever photo editing!

Thunder & Lightning

Storm 30th October 2016 Saint Helena Island Info Weather and climate
Storm, 30th October 2016{c}

Thunderstorms are sometimes seen out at sea, but until recently the last recorded thunderstorm over the island was on 9th June 1981. No damage was reported.

Amusingly, on 25th October 2016 the Government of St Helena issued a warning for consumers to reduce water consumption, saying there was no significant rainfall forecast over the coming weeks. This was followed 5 days later by a full-blown thunderstorm over the island, in the evening of Sunday 30th October. It was first noticed around dusk and continued well into the early hours of Monday morning, with bright intra-cloud lightning and loud thunder. A few Saints were terrified, never previously having experienced a storm such as this. No damage was reported. After the storm passed away from the island lightning was seen discharging into the sea.

Previous big storms include that of 21st October 1897, which lasted two days and produced hail stones a ½inch in diameter. Others recorded were on 22nd November 1874, 2nd October 1888, 22nd September 1890, 29th September 1891, 16th September 1894, 18th October 1905, 19th November 1914 and 4th November 1945 (there are no earlier records; either they didn’t occur or the East India Company didn’t consider thunderstorms worthy of note). It can be seen that they mostly occur in our Spring. The cluster in the late 1800s is interesting but probably not significant.

There are some reports of thunderstorms sometime in 1979, and another on 20th November 1985, but these are not in the Records.

Storm 30th October 2016 Saint Helena Island Info Weather and climate
Storm, 30th October 2016{d}

Saint Helena Island Info Weather and climate
{d}

Saint Helena Island Info Weather and climate
{d}

Saint Helena Island Info Weather and climate
{e}

’Rollers’

Storms out at sea sometimes result in an abnormally high swell in James’s Bay, and in recorded history a few times the waves have been powerful enough to cause damage. But nothing in recorded history ever matched the Rollers of February 1846. Read more on our Rollers page.

The aliens are coming!

The unusual cloud formation seen below was observed over St Helena on 6th January 2016. As far as we can tell it didn’t precede an alien invasion{8}. It appears to be of type altocumulus lenticularis.

AutoCumulus cloud seen over St Helena 6th January 2016 Saint Helena Island Info Weather and climate
AutoCumulus cloud seen over St Helena, 6th January 2016

It never rains…

Exceptional flood in Jamestown Saint Helena Island Info Weather and climate
An exceptional flood in Jamestown; usually the driest part of the island.

Hypothermia. On St Helena?

Napoleon’s retreat from Moscow Saint Helena Island Info Weather and climate
Napoleon’s retreat from Moscow{2}{f}

We understand that the lowest temperature ever officially recorded on St Helena was 8°C, and yet there is a story of somebody suffering from Hypothermia. It goes like this…

An ‘elderly’ gentleman (thought to have been in his 70s) was visiting the island. Despite his age he was fit and strong and an avid walker. One day he decided to attempt The Barn. All went well but when he was on the top low cloud descended without warning (as it often does), reducing visibility to near-zero. Aware that The Barn is basically an uneven plateau surrounded by steep cliffs, and being unsure of the path and his orientation, he decided to camp-down and wait for the visibility to improve; which it did not, and darkness fell. Missed from his accommodation a search party was sent out the following morning. Fortunately he had told others his route, so he was quickly located atop the barn, but after a night in the cold with no warm clothing he was found to be suffering from mild Hypothermia. He was taken down to the Hospital where he quickly made a full recovery. None the worst for his adventure, our unknown walker has the distinction of being St Helena’s only recorded case of Hypothermia. If you can help us verify this story please contact us

Read More

Below: Article: Four seasons in one day - Winter in St Helena and El NiñoArticle: Stunning Cloud Swirls Spotted by Satellite

More stories on our page Read articles about St Helena.

Article: Four seasons in one day - Winter in St Helena and El Niño

From Notes from a (very) small island 29th August 2015{9}{10}

Wind-pruning example Saint Helena Island Info Weather and climate
Wind-pruning example

I have blogged about the weather on Saint Helena before. But being British it’s obviously a pretty much inexhaustible subject and always a conversation saver. The musically educated amongst you will also recognise yet another song title here and Crowded House themselves seemed to like singing about the weather, particularly using it has metaphors for feelings in their writing. But for this blog ‘four seasons in one day’ isn’t a metaphor it’s the daily reality of winter in St Helena. My last blog on the weather was about the micro-climates on the island, where you can be in a cloud forest in area but within a mile be in bright sunshine and not be able to see a cloud in the sky. At least though to experience this you had to travel somewhere, now it’s got to winter you can just choose a spot, stay there and let all the different weather patterns come to you.

This is my first full winter here, last year I returned to the UK for the whole of August which is what would be decribed as mid-winter here. In fact, it’s not described as mid-winter at all, it’s called ‘Scruffy August’ in a lovely turn of phrase that is meant to describe the higher winds, more cloud and greater levels of rain that are meant to hit the island during this month. In reality that has hardly been the case. This morning, at the end of winter the sun is shining, there isn’t a cloud in the sky and it’s about 24°c. Winter here has basically been like a British summer, it’s never got lower than 16°c in Jamestown, I’ve even be sunburned a couple of times. ‘Scruffy August’ itself really hasn’t materalised at all, in fact August has been pretty much like August at home, the odd scorcher, the odd cloudy day and the odd spot of rain.

The bad weather seemed to come a bit earlier. June and July were a bit cooler, a bit greyer than they usually would be and it was these days that would often have the ‘four seasons in one day’, apart from the snow, I don’t think it has ever snowed here{11}. Generally the days followed a similar patter, wake up to a grey and rainy morning, which has been blown out to sea by mid morning leaving a lovely warm afternoon before turning windy, grey and wet again in the early evening. In all honesty, I can cope with that, get the rain out of the way during the night leaving lovely sunny days for us to enjoy.

One of the causes of this slightly different weather pattern of an earlier winter but with a much nicer August could be that this is an El Niño year. El Niño impacts on the climate because of changes to the world’s ocean flows, so being a small island in the middle of thousands of Km² of open ocean then it would be bound to have an impact here. The recent weather patterns certianly seem to have not matched past experiance, although this is purely anecdotal. Perhaps more interestingly the Humpback Whales started appearing in the island’s waters much earlier than usual. Prime whale spotting time is generall from about now until November, but they’ve been here for about the past 3 months. Of course, whales are in the waters all the time, but not in sufficient numbers to guarantee spotting them and not usually breaching to make the spotting even easier. But I have been seeing them from the beach, from my walk up Jacob’s Ladder and even from my office window. It’s one of the real treats of living on an oceanic island and something I can’t imagine that I will ever tire of.

Article: Stunning Cloud Swirls Spotted by Satellite

Three wonderful images of St Helena taken from space. Explanations below.

Image 1 Saint Helena Island Info Weather and climate
Image 1{g}

Image 2 Saint Helena Island Info Weather and climate
Image 2{g}

Image 3 Saint Helena Island Info Weather and climate
Image 3{g}

 

Image 1

From Our Amazing Planet (livescience.com) 27th November 2012{9}

Alone in the South Atlantic Ocean sits the small volcanic island of Saint Helena. The towering peak of the island disrupts clouds as they pass overhead, creating swirling patterns called von Karman vortices that can be seen by satellites overhead.

The swirling clouds, moving to the northwest over Saint Helena, were snapped by NASA’s Terra satellite on Nov. 15, 2012, according to NASA’s Earth Observatory.

Von Karman vortices are created when a mass of fluid, such as water or air, encounters an obstacle, and creates swirls going in alternating directions. These so-called ‘Von Karman streets’ can be seen in satellite photographs of clouds around the world.

Saint Helena is dominated by Mount Actaeon, which reaches up to 818 metres.

Image 2

Cmdr Chris Hadfield, one of the astronauts on the International Space Station, snapped this shot of St Helena and posted it on Twitter. Given the importance to St Helena of fishing we think maybe this image should become part of the national flag.

Image 3

Taken by NASA’s Earth Observatory, 10th November 2015.

Closing Humour Saint Helena Island Info Weather and climate

Laugh at funny Weather and climate humour LOL Saint Helena Island Info


Credits:

{a} ‘St Helena: A Physical, Historical and Topographical Description of the Island, including the Geology, Fauna, Flora and Meteorology’, by John Melliss, published in 1875., 1875{9}

{b} Reproduced{9} with permission from South Atlantic Media Services Ltd (SAMS)

{c} Dion Yon

{d} Bruce Peters

{e} Simon Ashley Yon

{f} Adolph Northen, 1828-1876

{g} Earth Observatory, taken from the ISS



Footnotes:

{1} Showing the wind direction on each day of a year.

{2} Many of his troops died of Hypothermia.

{3} It’s not always realised but when you are on the water you get a double-dose of the sun - once from above and again reflected off the surface of the sea.

{4} Which means if you organise a major outdoor event, even in the middle of the dry season, you should anticipate rain.

{5} So named because in the olden days there was no point in wearing your finest for Church on Sunday because you would get all muddy walking there, so people habitually ‘dressed down’ at this time of year.

{6} The data show that March has the most rainfall, and also the most sun-hours. We cannot explain this apparent contradiction. If you can help, please contact us.

{7} So now you know. If you can translate this into layperson’s terms, please contact us!

{8} Though if the aliens have secretly taken over people’s bodies in preparation for an invasion, nobody has yet noticed.

{9} Reproduced for educational non-commercial use only; all copyrights are acknowledged.

{10} See more blogs.

{11} Correct - it hasn’t.



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