You step outside on a summer morning in Monkton Heathfield. The thermometer reads a pleasant 18°C — hardly scorching. Yet within ten minutes of your walk or jog, you’re dripping with sweat, your heart is pounding, and you feel like you’ve run a marathon. The culprit isn’t the temperature. It’s the humidity.
What Humidity Does to Your Body
Your body cools itself primarily through evaporation. When sweat evaporates from your skin, it carries heat away — a remarkably efficient system that keeps your core temperature within a safe range during exercise. But when the air is already saturated with moisture, sweat can’t evaporate effectively. It beads up, rolls off, and does very little to cool you down. Your body responds by producing even more sweat, which only makes things worse. Meanwhile, your core temperature rises, your heart rate climbs faster than it would in dry conditions, and your perceived effort shoots through the roof.
Research has consistently shown that performance begins to decline around 60% relative humidity when combined with warm temperatures, and the effects become pronounced above 80%. For context, a typical humid summer morning in Somerset can easily sit in the 70–90% range — well into the territory where your body struggles to keep up.
Why It Feels Harder Than the Thermometer Suggests
This is where the concept of feels like temperature comes in. The Met Office combines air temperature and humidity (along with wind speed) to calculate an apparent temperature — what it actually feels like to your body. On a 20°C day with 85% humidity and little breeze, the effective temperature your body experiences can be several degrees higher.
Here in Monkton Heathfield, where the surrounding fields and hedgerows hold moisture after rainfall, local humidity can remain elevated well into late morning — even when the sky has cleared. If you’re planning a run or a brisk walk along the lanes or a session in the garden, checking the humidity reading alongside the temperature gives you a far more realistic picture of how demanding it will be.
Dew Point — The Number That Really Matters
Relative humidity is a percentage, which makes it somewhat misleading. At 15°C, 80% humidity feels quite different from 80% humidity at 25°C.
Meteorologists increasingly refer to dew point – the temperature at which air becomes saturated and condensation forms. A dew point below 10°C is comfortable for exercise. Between 10°C and 15°C, things start to feel sticky. Above 15°C, the air is oppressive, and above 20°C, it becomes genuinely dangerous for prolonged exertion.
The weather station on this site reports humidity and you can estimate the dew point from the temperature and humidity readings using the formulas explained in our earlier post on dew point.
Practical Tips for Exercising in Humid Conditions
Acclimatise gradually. The body adapts to heat and humidity over 7–14 days of repeated exposure. If you’re starting a new exercise routine in summer, begin with shorter sessions at lower intensity and build up.
Hydrate before, during, and after. In humid conditions, your sweat rate increases — sometimes dramatically — even though less of that sweat is actually evaporating. You’re losing fluid without the cooling benefit, which means you need to drink more, more often.
Time it right. Early mornings in Monkton Heathfield often carry the highest humidity from overnight cooling and dew. Mid-morning, as the sun warms the air and burns off surface moisture, can actually offer better conditions — even if the temperature is slightly higher.
Listen to your body, not your watch. In humid conditions, your pace will naturally drop even at the same effort level. Trying to match times set on crisp, dry autumn mornings will push you into the red zone. Respecting the conditions isn’t weakness — it’s smart training.
Watch for warning signs. Dizziness, nausea, chills despite the heat, or ceasing to sweat are all signals to stop immediately, find shade, and hydrate. Heat exhaustion can develop quickly in high humidity.
Why This Matters Locally
Somerset’s geography — a mix of low-lying ground, agricultural land, and proximity to the Bristol Channel — creates conditions where humidity can persist longer than in more exposed locations. The Met Office forecast on our Looking Forwards page includes humidity projections for the coming days, so you can plan ahead. Whether you’re walking the dog around the edge of the cricket field, tending the allotment, or working through a Couch to 5K programme, understanding humidity transforms a vague feeling of “it’s muggy out there” into a practical tool for managing your health and performance.
The Monkton Heathfield weather station provides live humidity readings on our Today page, updated continuously from our Davis Vantage Vue instruments. Check the conditions before you head out.