September and October are pretty difficult times to forecast weather in the UK. Why? Because of hurricanes. No, we are not directly impacted by hurricanes in the UK, however as the remnants of such systems (termed as post tropical cyclones) interacts with our weather patterns, they can “reek havok” in the Meteorological sense. Not in terms of huge wind speeds, however than can generate very windy conditions, (as seen with Ophelia in 2017), however more often in the sense of uncertainty in the forecast, and generally muggy weather.
If you look at the chart below, which shows the path of all Atlantic tropical systems since 1851, you will see that most hurricanes do a “curve up” from the eastern seaboard of the U.S. towards the British Isles. Granted, the sea temperature, which is required to be high when tropical storms / hurricanes are active, is much lower (colder) towards the British Isles of course, which means these storms loose their “tropical nature”, and ferocity, and become more like “normal areas” of low pressure.
However, since these systems have “tropical origin”, the air associated with them can be quite warm, especially if it involves a ridge of high pressure. However, there is often very high levels of moisture to, which does often lead to cloud. A “cloudy, warm and muggy” scenario is possible if a post tropical system affects the British Isles.
Hurricane Lorenzo, a currently Category 4 hurricane, is doing something a bit strange. It has taken a more easterly track, which means it could pump up some warm and muggy air, but also some potentially quite strong winds, this time next week (say 3rd to the 5th of October). More eastern areas should be drier, and potentially sunny, with the west seeing cloud, however most areas should be fairly warm during that time, thanks to Hurricane Lorenzo’s activity.
However, before we reach that stage, it is actually due to get quite cold and potentially very wet (early next week), thanks to a completely different area of low pressure. Temperatures are due to dip below average early next week, especially by Tuesday, due to a northerly wind. This may even produce some flurries of snow for the Scottish Ski resorts (above 3,000ft), and possibly some frosts in the North. There is also the chance of some very wet weather early next week due to a “clash of airmasses”. Warmer, wetter Atlantic air clashing with cold Arctic air is almost always a recipe for heavy rainfall at this time of the year. The GFS model, as seen below, indicates that by Wednesday next week many areas could have seen 2 inches or more of rainfall, producing a risk of flooding early next week.
Then things potentially become warmer later in the week thanks to tropical air associated with Hurricane Lorenzo (but it wont be a hurricane when it affects us), but that has been discussed earlier.