Nick L

It's because it's a much higher temperature. Relative humidity is simply a measure of how much moisture is in the air as a percentage of the maximum possible. Warmer air can hold much more water than colder air. Therefore an air mass at 30C will have a lower relative humidity than an air mass at 20C with exactly the same moisture in both. In your examples, you have a dew point of 19C, mushy has a dew point of 18C - you have almost identical absolute humidities (the amount of water vapour per cubic metre of air). Dew point is a much better measure of water content of the air.

The problem with Heathrow having a stab at it though is that it's not in the bowels of London, meaning the urban heat island effect is less pronounced - it loses heat fairly quickly. Never say never though.

Yeah but the best part about foreign holidays is that you can enjoy the weather by doing naff all but sit by the pool, drink some cold ones, and go to bed in an air conditioned room. "Foreign holiday weather" when I have to sleep in a flat that's 30C and then go to work in the morning? Nope. No thank you. This has to be up there as one of the most unpleasant, uncomfortable evenings I've ever experienced in this country. The sweat is pouring off me.

It's still above 30c in several locations, despite the sun having set. Unbelievable heat. Absolutely horrendous this evening.

An area roughly in the triangle of the M4/M5/M40 is really churning now. Should think it's only a matter of time before fun and games begin.

Hi Jamie, welcome to the forum. Would you mind popping your location in your profile please so we know where you're posting this from? Cheers.

The relative humidity will have dropped because your temperature has increased. All relative humidity is, is a measure of the amount of moisture in the air compared to how much it can possibly hold. Warmer air holds more moisture, so if the level of moisture in the air remains the same your RH will decrease as the temperature increases. I'd recommend looking at dew points instead of RH for an idea of moisture.

Well you were never really forecast anything today so I don't see the issue?

What direction are you looking here?

It's not even 4pm! When we're storm chasing stateside on most days it's barely even started by 5.

Apologies, typo in that link! wxcharts.com

You can find them at www.wxharts.com

Yeah.

35.3C now. 36 is still possible knowing that site.

34.9C at Heathrow, date record has gone. 5 miles away at Northolt, it's only 32.8...

34.6C at Heathrow, the date record is almost certain to go (34.7)

And then 10 minutes later, it's up to 33.6C. Clearly an A380 took off...

Frustratingly, it reached 33.1C and has since dropped to 32.6C. A really odd site.

I get the 10 minute SYNOP data at work, perks of the job!

Should comfortably hit 36 today! No high level crap coming in to ruin it yet, so can't rule out 37.

32.2C at Heathrow now, it is rocketing!

31.8C at Heathrow at 11:20. For comparison, last Friday (which exceeded 36) was only 31.4 at midday!

28.3C at Herstmonceux at 09:40, toasty!

Heathrow is 4C ahead of this time yesterday. 9am yesterday was 21.8C, it's currently 25.8C. As an aside, I'm highly dubious of the 35.5 yesterday. It was flatlining at 34C for a couple of hours, and then one random ob at 5pm shot up to 35.5, before dropping back to 34C.

34.6C at Heathrow at 3pm.