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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 first settled by the English, so of course we like to talk about the weather…

Clouds over the St Helena coastline

Below: Sun • Wind • Rain • Seasons • Expected weather • Current weather • In more technical terms… • Unexpected weather • Read More

All recent weather data recorded at, and kindly provided by, our 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

St Helena is in the Southern Hemisphere, north of the Tropic of Capricorn, which means the midday sun is directly overhead during the summer (see the article ‘The shortest and longest days’ below). The temperature can reach 34°C in Jamestown 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 coolest 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

Wind direction {1}
Wind direction{1}

Being within the range of the South-easterly Trade Winds stops the weather from becoming uncomfortably hot and keeps the air fresh, even in the enclosed valleys such a Jamestown. This is one of the reasons{4} why our air-quality is unimaginably high throughout the island. 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

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{5}. That being said, the main wet periods are in March (the ‘Lent Rains’) and August (‘Scruffy August’{6}). 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. August 2018 was the wettest August on record, with 106mm recorded at the Meteorological Station - that’s around 175% of the usual value; a truly ‘Scruffy August’. The record rainfall in a 24-hour period is 48.6mm, recorded on 26th April 2017, on which day the typical rainfall for a month fell in just 6 hours - when it does rain it can be heavy!.

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

Sun, wind and rain

Seasons

Seasons

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. Christmas falls in the summer!

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

Sunrise and sunset

Sunrise
Sunrise{7}

Sunrise
Sunset

St Helena is located close to the equator so our day-length does not vary greatly around the year.

In mid-winter sunrise is at around 06:50h and sunset at around 18:00h, a day-length of 11h10m. In mid-summer sunrise is at around 05:50h and sunset at around 18:50h, a day-length of 13h00m. The variation is therefore only around 15%.

The sun is directly overhead on or around 5th February and 6th November - see also the article (below).

If you like your information diagrammatically:

Weather chart

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 taken at the station over the years 2001-2018 (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:

‘Sod’s Law’

It could be argued that, in some respects, our weather is controlled by ‘Sod’s Law’ - the rule that basically says that everything is out to get you. The primary holiday time for the entire northern hemisphere is August, which is one of our coldest and wettest months, and heavy seas are normal in January-February which is exactly when most Cruise Ships call and when The Governor’s Cup and other yachting rallies arrive. See also the Closing Humour image (below).

On the other hand, our winter may be colder than our summer but it's still often warmer here in August than it is in London, and we have a warm and mostly-sunny Christmas which makes St Helena an ideal place to escape the cold, dark northern hemisphere winter.

Some you win…{9}

For countryside this green you have to expect a little rain
For countryside this green you have to expect a little rain…

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 - new tab/window - links to WeatherUndergound.com/

Our Meteorological Station

Our Meteorological Station opened on 1st September 1976, replacing an older station at Hutts Gate. It is located in Bottom Woods, 15°55”48’W 5°39”36’S, 436m above sea level.

It takes daily ground weather readings, and releases a daily weather balloon to measure upper atmosphere 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}

See the article (below).

The Meteorological Station at Bottom Woods
The Meteorological Station at Bottom Woods

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 sub-tropical southeast Atlantic is subject to dramatic inter-annual 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 eigen function (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.{10}

Unexpected weather

Thunder, lightning, or storms, rarely disturb the serenity of this mild atmosphere.
From ‘A Descriptive Sketch of The Islans of St Helena’. Wallis, London, 1815.

As with weather elsewhere, conditions sometimes exceed normal expectations…

Below: Things we don’t get • Thunder & Lightning • ’Rollers’ • Aliens are coming! • It never rains… • Hypothermia. On St Helena? • Wet decade…

Things we don’t get

Hurricanes, typhoons, tornados & dust storms

Global cyclone tracks
Global cyclone tracks

It is generally true that we don’t get any of these. Wind speeds up to 80Km/h have been recorded but are very unusual. See the diagram (right) regarding cyclones. However, listen to the report below to Radio St Helena in October 1993 by John Bailey (not a man given to fantasy)…

Whirlwind, John Bailey

Click here to hear this audio file

Click To listen

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.

We rarely get thunderstorms; when we do they cause great excitement!

Snow in Blue Hill? No, just clever photo editing!
Snow in Blue Hill? No, just clever photo editing!

Thunder & Lightning

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.

The images below are from the storm on 30th October 2016:

Storm, 30th October 2016
{c}

Storm, 30th October 2016
{c}

Storm, 30th October 2016
{c}

Storm, 30th October 2016
{d}

Storm, 30th October 2016
{e}

 

’Rollers’

Storms out at sea sometimes result in an abnormally high swell in James 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{11}. It appears to be of type altocumulus lenticularis.

Auto-Cumulus cloud seen over St Helena, 6th January 2016
Auto-Cumulus cloud seen over St Helena, 6th January 2016

It never rains…

An exceptional flood in Jamestown; usually the driest part of the island.
An exceptional flood in Jamestown; usually the driest part of the island.

Hypothermia. On St Helena?

Napoleon’s retreat from Moscow {2}
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

A wet decade…

The 1850s seem to have been a very wet decade, with many incidents of trouble with rain or the sea{12}:

22nd February 1753: Some very heavy showers of Rain which fell Tuesday last (18th) upon the Hills near Banks’ brought such great and impetuous Torrents of water down that valley as did much damage to the lower Platform there.

3rd September 1753: By a very heavy Sea such as never was known in the memory of any man upon the Island some damage was lately done to the old Battery at Sandy Bay.

22nd October 1753: The Guard House at Lemon Valley washed away by an unusual torrent of Water occasioned by some heavy Rains - likewise a Breast-work at Break Neck Valley.

20th January 1755: High surf damages fortifications in several places. (High surf or rollers during January also recorded as damaging property and sea defences in 1771 & 1787.)

8th September 1755: Some very High Surfs have lately washed away the Earth and undermined parts of the Works at Ruperts and done damage to those at the Main Fort.

29th June 1756: Council fails to meet due to a large Torrent of water coming down this valley which ran with such rapidity out of its common course that it was not possible to turn it until the Runs abated and therefore it has done great damage to the Fortifications and Plantations as well as to many of the possessions of the Inhabitants.

This may have included an El Niño period, but the phenomenon has only been recorded since the beginning of the 20th Century.

Read More

Below: Article: The remote weathermen charting the climate crisis • Article: Four seasons in one day - Winter in St Helena and El Niño • Article: Stunning Cloud Swirls Spotted by Satellite • Shortest and longest days

Article: The remote weathermen charting the climate crisis

By Mike MacEacheran, The Guardian, 26th July 2019{13}

Guardian 20190726 01

The Met Office team on a south Atlantic island reveal the extreme lengths they go to in order to forecast the weather

From left: Met Office weathermen Murray Henry, Marcos Henry and Lori Bennett
From left: Met Office weathermen Murray Henry, Marcos Henry and Lori Bennett
Launching the balloon at 11:15am
Launching the balloon at 11:15am
Hydrogen fills the balloon
Hydrogen fills the balloon
Marcos Henry, adjusting a cable in the meteorological station’s ‘weather garden’
Marcos Henry, adjusting a cable in the meteorological station’s ‘weather garden’
An anemometer, which measures wind speed
An anemometer, which measures wind speed

At 11:15am on a blustery spring morning, Lori Bennett stands on an exposed bluff on the remote south Atlantic island of St Helena, holding a gigantic, wobbling balloon. The wind is roaring, waves are churning up a swell and the sea air is charged with industrial hydrogen pumped from a nearby outhouse and used for blowing up the inflatable.

The Met Office station manager, born in Northern Ireland and now living half a world away from his friends and family in Swindon, is a picture of calm in a drab boiler suit, old ski goggles and a flash hood he jokingly calls his Star Wars outfit. Moments later, he prepares to let the weather balloon slip from his fingers. Swinging it around, so that it lifts straight up rather than floating across the weather station car park, he is soon watching it jiggle steadily upwards before it disappears into the clouds.

They’ve been known to scare the life out of pilots, says Bennett, flipping his goggles off. But out here in the middle of nowhere we don’t get many planes. As well as launching the balloon in 45-knot winds that can pull your arm off, Bennett’s main worry is the hydrogen used to fill it. A spark of static could detonate the gas inside the warehouse and violently blow the doors clean off. You wouldn’t walk away from that, he says, matter-of-factly.

It affects people’s lives every day - we’re the frontline in Atlantic forecasting

Sometimes, it is easy to forget the lengths to which meteorologists go to bring us forecasts: telemetry instruments and synoptic codes don’t really figure in the chitchat of TV weather presenters such as Carol Kirkwood and Tomasz Schafernaker. But as the climate crisis gains new urgency, our understanding of weather systems and patterns is more important than ever - and the weathermen working here are key to that. Among the last in the world to use such analogue methods as weather balloons, they are guardians of a dying art.

The Met Office has five other operational locations outside the UK (Antarctica, from October to April; Ascension Island and the Falkland Islands in the south Atlantic; Gibraltar and Cyprus), but none as unreachable as this tiny British overseas territory. The far-flung volcanic outpost doesn’t just filter data into global forecasts to help predict whether your summer bank holiday will be a washout; it plays a vital role in tracking how our climate is changing over time. Added to that, the south Atlantic is a hotbed of geomagnetic activity - something many experts believe is a factor driving the climate emergency. Crammed into Bottom Woods station, little more than a humble portable at the end of the Earth, are complex instruments sounding a warning to anyone who will listen.

After precisely 90 minutes, Bennett’s balloon reaches a height of 100,000ft, where the air temperature hovers around -80C; the giant latex ball has stretched to the size of a two-storey house. It is used only once and will eventually burst somewhere on the edge of the stratosphere, but not before a mini weather station, known as a radiosonde and attached to the neck of the balloon, can relay back data on temperature, moisture, pressure, visibility and radiation. With Whitney Houston’s One Moment In Time drifting out of the weather station’s FM radio, it is the oddest science lesson you could imagine. Bennett sometimes imagines himself flying away with the blimp, he says, like the balloon salesman Carl Fredricksen and his cartoon house in Disney’s Up: Just working in this quiet place gives me the freedom to dream.

As the wind continues to whirl across the balloon launch site, the station manager introduces me to the rest of the team. St Helena’s weather station has been operational since September 1976.

Satellites only do so much. Honestly, there’s still nothing as reliable as a land-based station

Technical manager and islander Marcos Henry, 58, has been working at the station since leaving school at 16. He says the balloon procedure - one daily launch, always at 11:15am - is effectively the same as it was 43 years ago. The weather never stops, he says, although he notes that they used to launch two balloons a day, before cost-cutting measures started to bite. Sunday is now launch-free - and sometimes the four-man team are stretched.

Today, Marcos is joined by 28-year-old Murray Henry, his island-born cousin, but not Garry Mercury, another (appropriately named) scientific observer; he is at the dentist with toothache. If there are any further staffing issues, one of the local bin-men has been trained to act as a substitute. You can’t really put a value on what we do here, says Marcos, as a gritty light begins to spill through the clouds. We have a collective responsibility to gather information, because it affects people’s lives every day - we’re the frontline in Atlantic forecasting.

I follow the three men into the office, which is topped with VHF antennae and fortified with a clunky array of instruments, including a broken anemometer that once measured wind speed, an obsolete sunshine recorder and a bank of computers that transmit data back to Met Office HQ in Exeter. It feels like a place that exists in a different era. Satellites only do so much, says Marcos, with one eye on the readings coming in from the balloon. Honestly, there’s still nothing as reliable as a land-based station.

The St Helena unit is just one of 190 stations that make up the Global Climate Observing System (GCOS), which is co-run by the UN, Unesco, the International Science Council and the World Meteorological Organisation to monitor activity in the Earth’s upper atmosphere. As a key station in the south Atlantic, its data is vital for climatological studies, and its old-school methods have made the men unlikely rock stars on the island. Everyone wants to see the big balloon, says Bennett.

St Helena is 5,000 miles from the problems of BREXIT Britain, boasts black-sand beaches, Galapagos-like giant tortoises and all manner of indigenous birds. Yet that is mixed with reassuringly familiar snapshots of the UK: homes in the British overseas territory are decorated with pictures of the Queen, shops stocked with bottles of HP Sauce and cans of Irn-Bru.

What also characterises the island is its topographical weirdness. With its odd mesh of rainforests and moon-like tablelands, the landscape changes abruptly from Yorkshire Dale to Jurassic Park, while the night skies are a blowout of frighteningly bright nebula. Small wonder Bennett - as well as Charles Darwin and Edmond Halley - fell for the place. As in the UK, there is plenty of talk about the weather, too.

Have its forecasters noticed signs of the climate crisis? Bennett says he has little doubt. The wettest day since the weather station opened came last February, with 49mm of rain in just 24 hours. Marcos remembers a time growing up on the island when streams flowed freely; recently, they have dried and turned to dust. There have been landslides and rock falls, too, he says. In the 90s, the island recorded 4,543mm of rain, a figure that soared to 5,148mm over the following decade. So far, from 2010 to this March, the weathermen have seen levels rocket beyond anything on record.

One complex meteorological instrument under the team’s watch is the Marvelesque Sun Sky Lunar Multispectral Photometer, which feeds into a global network to monitor pollutants in the atmosphere; growing levels are a clear indicator of how we need to change our habits. There is also an automated radionuclide station, which recently picked up nuclear particles from the Fukushima Daiichi disaster in 2011, and continues to search for evidence of nuclear tests.

Across the island, in the air traffic control tower overlooking St Helena’s airport, another Met Office scientist, Timothy Baker, is contemplating the same clouds. The meteorologist has been at his desk since 4am creating a forecast to ensure the safe arrival of the biweekly aircraft from Johannesburg, the island’s principal connection with the outside world. (The airport opened for commercial flights in 2017.) His hope is that the bank of low stratus to the south will relent in time, otherwise the plane will have to turn around, 1,100 miles into its journey.

It’s a complex place because of how quickly the weather can change, he says, as radio static from a console begins to cut through his words. Four seasons in one day? It’s more like 12. It can flip from sunshine to thick fog within minutes. Sometimes, they can’t see the fuel barrels on the apron [where planes are parked] from five metres.

As I come to realise, the usual norms rarely apply here. Along with a colleague at Heathrow and a handful scattered around RAF bases, Baker is in the unusual position of being a weatherman embedded at an airport, working in tandem with the Bottom Woods team. Other airports rely solely on remote forecasts.

On the day I leave, clouds are billowing over Diana’s Peak, the mountain that looms to the west of the airport. The plane accelerates and all I can think of is the ends-of-the-Earth weathermen, enveloped in cloud, predicting sun patterns, rain showers and crosswinds. We have become so used to weather updates on TV, radio and phones that we have stopped seeing the act’s grandeur. To visit St Helena - to see Bennett, Marcos and Murray launch their balloons into space - is a chance to glimpse that absorbing strangeness once again.

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

From Notes from a (very) small island 29th August 2015{13}{14}

Wind-pruning example
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 described 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 materialised 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{15}. 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 certainly seem to have not matched past experience, 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 generally 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
Image 1{g}

Image 2
Image 2{g}

Image 3
Image 3{g}

Image 4
Image 4{g}

Image 5
Image 5{g}

 

Image 1

From Our Amazing Planet (livescience.com) 27th November 2012{13}

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

An even more dramatic example of von Karman vortices, taken by NASA’s Earth Observatory, 10th November 2015.

Image 4

Taken by Oleg Artemyev from the International Space Station, 14th August 2018.

Image 5

Taken from the International Space Station, 8th October 2018.

The shortest and longest days

The Wikipedia inclusion on our On This Day page on 21st June 2018 prompted the following email:

Here’s a nerdy subject!

Your page ‘On this day’ for June 21st makes an embedded reference to the Solstice page of Wikipedia. One would hope that that was definitive enough, but it is not (an issue I have been grappling with for a long time). The problem is, the authors are well in the Northern Hemisphere (between the Tropic of Cancer and the Arctic Circle) and what they say is all well and good for such locations. For analogous locations in the Southern Hemisphere, the terms ‘Summer’ and ‘Winter’ need only be interchanged. But we are located within the tropics and things are different there (here).

It is all to do with solar system mechanics. The basic model (which underpins the general preconception as per Wiki) is that the sun’s highest point goes up and down in the sky during the seasons. All else being ignored, if you were to plot the sun’s highest point along a time axis covering a year, it should resemble a sine wave, and the approximations are good enough for most applications. The closer you are to a tropic, the higher the sun’s highest point (altitude) will reach (the amplitude of the sine wave). The Summer Solstice is then defined as the day on which the sun reaches its highest point.

On a tropic, the highest point is the zenith (that is pretty much what defines the tropic). What happens between the tropics though? For such locations as ours, the sun’s wandering up the sky actually overshoots - during the year, the highest reach of the sun gets higher and higher in the north and then… actually moves over to the south of us! Briefly. Then it returns to the north and declines again into winter.

Again, all else being ignored, we should have two longest days and two shortest days (the two spanning the relevant solstices by a few days in each case). But this is not quite what happens. And the reason that it does not happen like this is the following:

What this means is that the graph of the sun’s highest points does a strange wobble around the solstices and the length of the day graph is somewhat unexpected. For 2018, on St.Helena, the Shortest day (between sunrise and sunset) occurs on 13th and 14th June, then again on 17th - 24th June, and then again on 26th - 28th June. The Longest days are similarly spread out (17th, 19th, 21st, 23rd and 25th December).

Weird eh?

Have a look at www.gaisma.com/en/location/half-tree-hollow.html. The graph of sunrise and sunset times is apparently bizarre - but it explains why the day length over the year (the distance between the two wavy lines) is not what you’d simplistically expect.

Editor’s Note: Thanks, Stuart, for that fascinating and comprehensive explanation!

Laugh at funny Weather and climate humour - LOL

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{13}{b} South Atlantic Media Services Ltd (SAMS){13}{c} Bruce Peters{d} Simon Ashley Yon{e} Dion 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} Also there is no heavy industry on the island.{5} Which means if you organise a major outdoor event, even in the middle of the dry season, you should anticipate rain.{6} 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.{7} Note that we can only find a single image of a sunrise, but have enough sunsets to make a slideshow. This may be because most habitations are on the north/west side of the island, overlooking the sunset, and few are on the north/east side overlooking the sunrise. Or it could be there are rather more people around at 6pm than at 6am!{8} 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.{9} Incidentally, our Editor firmly believes that Sod’s Law is the unifying theory of everything that scientists have been looking for. Why do planets not obey the same physical laws as sub-atomic particles? To make physics difficult. Sod’s Law. Is Schrödinger’s cat alive or dead? If you want it to be dead, it’s alive, and vice-verse. Sod’s Law. Why is there not enough matter in the universe? Sod’s Law. randomthoughtssthljt.blogspot.com/2019/01/the-unifying-theory-of-everything.html.{10} So now you know. If you can translate this into layperson’s terms, please contact us!{11} Though if the aliens have secretly taken over people’s bodies in preparation for an invasion, nobody has yet noticed.{12} There was also an Earthquake on 7th June 1756.{13} Reproduced for educational non-commercial use only; all copyrights are acknowledged.{14} See more blogs.{15} Correct - it hasn’t.

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