Author: Eric Gilbert

Friday 10th July
The heat was excessive again on Thursday under the relentless, very strong sunshine under cloudless skies, that resulted in a maximum of 34.2C at 18.34. This high was a significant 11.3C above my long-term average and made it the warmest day since the peak of 34.9C on 25th June during the last heatwave. The past night held on to more of the heat overnight than previous nights, resulting in the warmest night this month as the thermometer did not drop below 15.3C, which was 3.3C above average.

Friday began with a little light relief from the very strong sunshine as it tried to break through the thicker, cloudy area above the eastern horizon, which limited its strength after 06.00 until around 07.30, however, by 08.00 the thermometer had already reached 20.7C as the sun’s strength built remorselessly.

Today is likely to bring the peak of the heatwave. Indications are, as I mentioned yesterday, that as the high pressure very slowly relocates northeastwards to arrive between Scotland and Iceland, the air flow will begin to come from a more easterly quadrant, which will mean a slightly cooler flow of air having travelled across the North Sea. However, the change must be kept in perspective, as we will still be under the dominance of the high pressure so the drop in temperature will be the odd degree, but however small, it will help to reduce the excessive heat. The advance forecast is that heatwave conditions will continue for another week.

It does look as if the peak of the current heatwave will not break my record for July as a maximum of 36.7C was logged on 19th July 2022.

An indication of the cumulative build up of heat during this heatwave was the time at which the air temperature reached the heatwave threshold of 27C each day over the past four days. It was logged at 15.12, 13.22, 10.38 and 09.09 today, respectively.

The soil temperature at a depth of 5cm, read at 08.00 daily, appears to have stabilised over the last three days with 24.7C, 24.5C and 24.7C respectively. However, as a matter of interest I read the thermometer at 20.00 last night when it had risen to 31.8C. The glass thermometer is right angled in shape with the scale on the horizontal section.

Thursday 9th July
The sun was relentless on Wednesday as soon as it got out of bed, that it eventually pushed the temperature to a maximum of 32.5C at 18.12. This high was a significant 9.6C above my long-term average making it the hottest day since 26th June. The sunshine was wall to wall that once again resulted in High UV light. Being so close to the centre of the anticyclone meant little movement of air, a maximum movement, couldn’t be called a gust, was just 9mph at 12.50. The heat was slow to dissipate under clear skies, however, a minimum of 12.6C at 05.31, half an hour after sunrise in Marlborough at 05.01, was just 0.6C above the July average. The breeze fell out just before 22.00 and it has been calm all night and also still this morning, both the high and low anemometers are stationary.

The blazing sun once again greeted the start of a new day on Thursday that resulted in a temperature of 23.2C at 08.00, which made it the warmest start to a new day, at that time, since 26th June in that heatwave. Today and tomorrow will bring the peak of the heatwave as the thermometer edges a little higher.

Under the intense heat the ground is still drying out with an equivalent loss of rainfall in excess of 5mm each day. So far this month the total loss due to evaporation from plant life and the ground is currently 43mm set against the 0.2mm that fell on the 1st, from light drizzle. As the heat builds and the ground continues to dry out, the humidity at the start of each new day, logged at 08.00, has reduced significantly. Today the humidity was 67% compared to that of three days ago of 83% and at the start of the month was 90%.

The centre of the high pressure is slowly relocating westwards, then northwards, that by Saturday will see it centred between Scotland and Iceland. This minor change in position will signify a distinct change in our weather, if only minor. The breeze will the have an easterly component, which means it will have traveled over the North Sea and we will see a gradual, if small, decrease in maximum temperatures. However, not to get excited, as the heatwave conditions are likely to persist right through next week and up to the following weekend that will then eventually bring some relief from the excessive heat, but maximum temperatures are still likely to be a little above average.

There is little sign of any useful rain in the forecast for gardeners, one forecast suggest that there might be light rain showers towards the end of next week but that is a long way off for any confidence in the forecast.

The Met Office released this article yesterday.

A marine heatwave could reach “extreme” levels around parts of the UK later this week, according to the Met Office, raising concerns for marine life.

Long periods of sea heat can trigger mass die-offs among some seagrasses, shellfish and other species, as well as encouraging greater numbers of warm-water creatures including octopus.

The heatwave is currently strongest off the coasts of eastern and southern England, and sea temperatures could reach 4-5C above average in places.

The marine heatwave has been fuelled by the “heat domes” that brought record-breaking air temperatures in May and June, on top of long-term ocean warming due to climate change.

Important marine habitats such as seagrasses and kelp forests are suited to cooler waters and can experience high levels of heat stress when temperatures surge.

This can reduce their growth or even lead to mass mortality events, which could have knock-on effects for species that rely on these habitats.

The UK has experienced marine heatwaves – prolonged periods of unusually high sea surface temperatures – before.
But scientists fear this event could be particularly intense and long-lasting, particularly for parts of the English Channel and the southern North Sea.

“We’re starting to see temperatures now that we would expect to see at the height of summer, [at the] end of August,” said Dr Zoe Jacobs of the National Oceanography Centre in Southampton.

Wednesday 8th July

I have today included a picture of a baby puffin taken on Skomer Island, which is called a puffling.

Tuesday began the new day with variable cloud that meant the rise in temperature was restricted during the first half off the morning, nevertheless, by 13.22 the heatwave threshold had been reached with a maximum of 29.9C at 16.51, which was 7.0C above my long-term average. The UV level at its peak was again Very High. The heat was slow to drain away overnight, however a low of 14.1C was logged at 05.36 early Wednesday, just after sunrise in Marlborough at 05.00, being 2.1C above average.

There was no thin cloud to minimise the strong sunshine at the start of Wednesday that resulted in a temperature of 22.9C by 08.00, which made it the warmest start to a new day at that time since 26th June. As the area of high pressure slowly changes the breeze today will be variable and light starting off with a northerly aspect before backing to have a more westerly component. The barometric pressure has begun to rise again with a reading of 1020.7mb at 08.00.

The past few days have seen minima above average but not so high as during the previous heatwave. The forecast is for this situation to continue for another week at least with at the moment, no possibility of tropical nights ahead, when the temperature does not drop below 20C.

The Azores ridge of high pressure is slowly edging northwards that will see its centre move to be between Scotland and Iceland by Saturday, which by then will see the air steam have a more easterly component, which will result in maxima drop a few degrees below the peak on Friday, but still in heatwave territory.

Yesterday I added paragraphs about the ‘cold blob’ in the North Atlantic. This was raising concerns amongst climate scientists and how it might affect the Atlantic Meridional Overturning Circulation (AMOC). Some more research adds detail to the recent concerns.

The AMOC is one of the two main engines of global circulation, which is why it is so important, as it brings warm Caribbean water towards the north. It emits that heat to the atmosphere and keeps us relatively warm here in Europe, before that water sinks and heads southwards.

I understand there are indications that the current system appears to have slowed down or changed – hence the cold blob.

Because the cold blob is so big it also affects the air above it. The jet stream, which we know has a major influence on our weather being a fast flowing current of air flowing from west to east, hits the cold blob and is forced to go around it. The result, I understand, is heat dumps and cold snaps, where it hits the bottom and then creates a wave in the jet stream that passes over Europe.

Much more research is needed to discover if the AMOC is slowing or changing but in the shorter term it is suggested that the cold blob could lead to more heatwaves in the UK, however, in the longer term there is the potential for the climate in northern Europe to get much colder due to the blob.

Tuesday 7th July
After a misty and cloudy start to Monday the persistent strong sunshine eventually pushed the temperature above the heatwave threshold of 27C that was reached by 15.12. The thermometer then slowly continued to rise, eventually peaking at 29.7C, logged at 16.52, being 6.8C above average. This was the hottest day since the 26th June (33.3C). Thicker cloud began to drift across from the northwest after 17.00 that then began to thin before a short lived clearance when more cloud arrived just after 04.30, hence the minimum of 14.3C was logged at 05.15, that stopped any further drop in temperature, which also coincided with sunrise in Marlborough at 04.59. The low was 2.3C above average.

We have now endured 24 consecutive days when the maximum was above average with many more to come! There have been 23 recent nights since 14th June that were also above average, BUT not quite consecutive, as a low of 6.9C was logged early last Friday.

Tuesday revealed a cloudy start to the new day with thin, high, fair weather cloud that, as mentioned above, arrived early in the morning. I noticed that around 07.45 the sun was beginning to slowly gain in strength to thin the cloud but not strong, although the temperature at 08.00 had eased upwards to reach 17.8C.

The centre of the Azores high has eased away a little to the southwest, hence the fall of 13mb since the 3rd, but it os still in command. Over the next few days it will continue to dominate our weather even though it slowly relocates towards the northwest of the UK, which will see the breeze veer into a northerly quadrant later today and for Wednesday before to backs again, when it is then forecast to arrive from the east by Friday. But be not fooled, as although we expect a cooler air stream from those two directions, in fact the heat will continue to build with a peak probably on Friday.

The long range forecast indicates that the heatwave conditions are likely to continue until around the 17th.

There is a ‘cold blob’ in the North Atlantic that is causing much concern amongst scientists. A giant cold patch has formed south of Greenland, which is the only place in the world to have cooled significantly since the 19th century. In fact, it has dropped nearly 1C since 1900. The drop in temperature first started to raise alarm bells about a decade ago, due to its swiftness and severity.

This cold blob itself could have a significant impact on our climate and weather systems, but scientists are worried that it might potentially suggest that something far more worrying is changing in our oceans. It could suggest that the cold blob is cold mainly because more of the water’s heat is passing from the ocean’s surface into the atmosphere. It might all be connected to the Atlantic Meridional Circulation (AMOC), a major system of ocean currents that moves water around the world – and it is this notion that is causing major concern – more tomorrow!

Monday 6th July
After a cool, cloudy start to Sunday the sun began to break through late morning and built after midday to reach a maximum of 27.2C at 15.59, being 4.3C above my long-term average. The heatwave threshold for Wiltshire of 27C was reached at 15.12 and lasted for an hour until 16.14 when variable light cloud drifted across resulting in the peak temperature beginning to slowly decline. A minimum of 13.8C was logged at 04.50 early Monday, just before sunrise in Marlborough at 04.58, being 1.8C above average.

In the early hours of Monday low cloud had drifted across that initially masked the top of the Marlborough Downs giving murky conditions but by 06.15 this had completely evaporated. The thin, high cloud will likely begin to recede as the morning progresses and the heat to build again.

Sunday was the start of the third heatwave of 2026. There is no doubt that an official heatwave will be declared on Tuesday when there will have been three successive days when the temperature reached or exceeded the Wiltshire threshold of 27C. In fact it is likely that this heatwave will exceed the seven days of the second heatwave in June, which will probably last up to the middle of next week when the temperatures are then forecast to moderate a little but still be well above average.

Although peak temperatures by Wednesday will likely reach 30C of above, the nights won’t be quite so hot as in the previous heatwave. However, they will still be a few degrees above average for July but thankfully no tropical nights are likely when the thermometer does not fall below 20C.

The Met Office heatwave threshold was updated ahead of summer 2022. The initial heatwave thresholds were calculated based on the 1981-2010 climatology of daily maximum temperature at the mid-point of the meteorological summer (15 July). The revised thresholds use the 1991-2020 averaging period introduced in January 2022. The geographical differences reflect the differences in climate across the UK.

Over the last few years there has been a push to install solar panels. While the panels work best in direct sunlight, they ironically don’t do as well in high temperatures – when the sun is at its strongest – due to how they generate electricity. It is not widely known that these panels begin to loose their optimum performance when the air temperature reaches around 25C and for every degree Celsius above that temperature the efficiency falls by around by 0.5%. More recent panels can cope better than earlier versions but still see a drop off in performance in heatwave conditions.

Latest: Heatwave threshold of 27C reached at 12.01