August 11th, 2025

As we approach the middle of August and this week, our fourth heatwave of the summer for England and Wales with temperature tipped to peak in the low thirties again across the southern half of the U.K. 2025 is truly shaping up to be a game changer weather-wise. We are also in a period of great uncertainty when it comes to forecasting with the outlook beyond 3-5 days changing daily.

Rhosilli beach - The Gower - a view I will never get tired of

I am just back from The Gower, a camping holiday I booked not 10 days before I departed. At the time, the GFS showed high pressure building and a stable weather situation. The reality was Storm Floris (not that bad really in Wales though the campsite refuse area was full of abandoned, broken tents and awnings the next morning). Storm Floris came out of nowhere forecasting-wise, a seemingly innocuous low pressure system that deepened quickly into a full-blown storm, our 2nd named August storm in the last 2 years, with Betty (the awning trasher) in 2023.

Walking along the footpaths I was struck by how autumnal it felt, with ripe Blackberries and Sloes and Hawthorn berries already turning red. I wonder how many of the latter will be available for the autumn Thrush invasion from Scandinavia if and when it happens because Redwings and Fieldfares are staying put for longer, coming over later and in diminishing numbers.

Reproduced courtesy of The Met Office OSTIA

One of the Key drivers for these storm systems and I believe the ones still to come this year is our increasing sea temperatures. Low pressure systems moving over warmer oceans pick up energy and temperature in a process known as Cyclogenesis. Temperature is crucial because for every 1°C increase in air temperature, the atmosphere can hold 7% more water vapour. So warmer seas mean more violent storms in my books carrying more moisture. As I have written about before, The Bay of Biscay is our key driver to damaging storms.

Looking at data from Copernicus (find it here) going back to 1850, the trend is clear ;

If we look at temperature data from around the U.K & Ireland using the truly brilliant My Ocean Pro mapping tool from Copernicus (find it here), we can see why The Bay of Biscay plays a key role in our weather. We can also see how the sea temperature just off Cornwall is significantly higher than The Atlantic to the west of Ireland and of course, The North Sea. So dependent on the path of a storm, the potential for cyclogenesis is there......

Produced courtesy of Copernicus.eu

No wonder that we are seeing massive changes in our sea life, with Blue Fin Tuna now regularly seen off the south west of England and Wales, feeding on our Mackerel and Garfish shoals. As I type this, BBC Radio 4 is discussing the massive increase in Octopus that we are seeing off our coasts. In the sea on The Gower, it was full of jellyfish, some large, some small, but lots of them. I made the mistake of fishing in the surf in my swimming shorts and picked up Jelly rash on both ankles, boy it stings, like Nettle rash on steroids !!!!

The increase in sea temperatures is also affecting our local climate and the ability of our forecasters to forecast accurately. Currently the accuracy of a forecast from Metoeblue at the 10-day mark is 20%, in other words, there's an 80% chance it will be inaccurate. This isn't a reflection on Meteoblue, more so on our changing climate and the difficulty trying to keep up with changes in weather patterns and their behaviour. A.I or no A.I.

7-day GFS projection - tropicaltidbits.com

So we know this week we have another heatwave for some areas but it won't be completely dry and hopefully night temperatures will be a little bit more bearable. The reason for this is of course that our nights are getting longer, so the potential for temperature to decrease overnight is increasing. At the Summer Equinox, the night length is around 17 hours. Today it is 15 hours and by the end of this month, 13.3 hours.

The animated GIF above for the next 7 days shows the current heatwave building but also returning at the end of the week. National forecasts show the heatwave building in the early part of this week and then dropping off to cooler temperatures. A contradiction that highlights the fact that our forecasting accuracy currently is very poor, so I won't waste my time and yours putting together a forecast that I believe is inaccurate once I have finished typing it. What you can see is that the west across Ireland, the west of England and Wales is cooler, as is the north and Scotland. Here it will also be more unsettled this week with a greater potential for showers coming into the weather picture.

Before I leave the weather forecasting part of this blog, I'd like to wish everyone involved in the DP World Tour Event at Furesø Golf Klub, Denmark to Thomas Pihl and this team, to all the volunteers and the club itself, a great tournament. Thankfully the weather forecast for this week is good for Denmark, with pleasant temperatures and increasing sunshine as we approach the weekend. I hope it stays that way for the event. Held og lykke!

A week later we have The British Masters at The Belfry, good luck to Angus and his team for that event and no 'wee man', I am not giving you a forecast today for your event for the reasons I have detailed above 😀

Agronomic Notes

Above I discussed the change in shortening day length / lengthening night length as we approach the autumn. This change is of course a driver for disease because with longer nights and cooler night temperatures, we have an increasing potential for dew formation and longer periods of leaf wetness. This is the driver for Microdochium, Dollar Spot and Anthracnose. Given that we have had a hotter summer, I wondered how leaf wetness levels compared vs. last summer, which we know was cooler and wetter. Surely this summer has been lower because the air has been drier ?

I looked at our default location, Thame, Oxfordshire and put together this comparison of the total number of leaf wetness minutes as measured by a Davis leaf wetness sensor (shown above) fitted to a Davis Vantage Pro weather station. I have continued the 2024 stats to show the trend in leaf wetness minutes into the autumn / winter using data from 2024.

2024 2025

May 11,719 11,337

June 4,183 6,011

July 8,926 3,482

August 9,391

September 13,356

October 18,641

November 11,962

December 18,485

Total leaf wetness minutes - Thame, U.K - 2025 vs. 2024

So if we look at July 2025 vs. July 2024 for this location, the number of leaf wetness minutes is significantly lower, some 61% lower to be accurate. So from a disease pressure perspective and specifically Dollar Spot and Anthracnose, July 2025 was a lower disease pressure month vs. its predecessor in 2024, but we still had a significant peak as you'll see later in the blog. The trend for August 2025 is also significantly lower than August 2024 as I type this because it has been hotter and drier. Of course this is one snapshot, one location and we already know that different regions of the U.K, Ireland and Denmark vary massively. The South West and south coast of England have always showed higher levels of humidity compared to say The Midlands, so there will be regional variations for sure.

Below is a regional chart showing Dollar Spot Probability as defined by the Smith Kerns disease model for a number of locations.

What is hopefully clear from the table above is the massive increase in total leaf wetness as we transition from August to September, so from a Dollar Spot perspective if you have seen some initial signs this summer, then you can expect a significant increase in pressure from this disease as we come into the autumn. Dollar Spot is a strange disease, for a pathogen that has been no.1 in the U.S for many years, there is still so much that we don't know about it.

We do know it survives on mycelial mats rather than spores and that's why if you have already seen existing activity (i.e. mycelium), the potential for more is there. August is the month to get your plans in place so you are not caught out. There is lots of info out there whether it's pesticidal control that's required, turf hardeners, dew control (manual or surfactant), rolling or a combination thereof.

Again here we have significant variability, for some clubs no sign of this disease, for others it affects higher-height-of-cut areas like tees, approaches, fairways only and for a growing number, it is also a greens disease. Not only a disease of fine turf but one that once it has been present is very difficult to regrow grass in the affected areas, a bit like Take All in this respect. Fingers crossed for the rest of August and September.

OK, that's me for another week, all the best to you.

Mark Hunt