Explanation Of Humidity

[winterfreak]

Many apologies if this is in the wrong place or a duplicated thread but we're off to Cyprus this week and i'm trying to 'understand' humidity. Currently for Paphos the temperature is 27°c with a rel humidity of 79% and a dew point of 23°c. Will this be sweaty unbearability or reasonable summer heat that won't leave us drenched in perspiration? Many thanks for any advice and, again, sorry if in totally wrong place.....

[cheeky_monkey]

love cyprus...sounds not to bad to me for cyprus..june is the best month of the year to holiday there IMO

[winterfreak]

love cyprus...sounds not to bad to me for cyprus..june is the best month of the year to holiday there IMO

That's good then , we're off to a family wedding but just wondered about the humidity? Any other explanations welcome and thanks CM!

[Backtrack]

Not got the time to write an explanation myself at the moment, so here's one from Wikipedia.

Humidity is a term for the amount of water vapor in air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of air and water vapor, and humidity is defined in terms of the water content of this mixture, called the Absolute humidity. In everyday usage, it commonly refers to relative humidity, expressed as a percent in weather forecasts and on household humidistats; it is so called because it measures the current absolute humidity relative to the maximum. Specific humidity is a ratio of the water vapor content of the mixture to the dry air content (on a mass basis). The water vapor content of the mixture can be measured either as mass per volume or as a partial pressure, depending on the usage.

In meteorology, humidity indicates the likelihood of precipitation, dew, or fog. High relative humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in a heat index table, used during summer weather.

Conversely, hot air attended by high relative humidity “feels†warmer than it actually is because of an increased conduction of heat to the body combined with a lessening of the cooling effect afforded by evaporation. On the other hand, a low relative humidity “modifies†the effect of temperature extremes on the human body. Humidity decreases with altitude. Proximity to large bodies of water and the prevalence of moisture-bearing winds favor high humidity. A temperature-humidity index has been developed by the U.S. National Weather Service that gives a single numerical value in the general range of 70 to 80 reflecting the outdoor atmospheric conditions of temperature and humidity as a measure of comfort (or discomfort) during warm weather. The temperature-humidity index, I_TH, is defined as follows: I_TH=0.4 (dry-bulb thermometer temperature F + wet-bulb thermometer temperature F) + 15. When the index is 70 most people feel comfortable; at 75 about half the population is uncomfortable; at 80 most are uncomfortable.

[k19]

Humidity is a measure of how much water vapour is in the air. Warm air can hold more water vapour than cold air.

The reason you often find 'humid' days uncomfortable, is because the air is near or at its saturation point (Relative humidity 100%) this means that the air can hold no more water vapour, so when you sweat, it cannot evaporate if the air is truely saturated. However in practice you will find it will evaporate, just not as much, which leads to people feeling 'sticky' and uncomfortable because they cannot cool down by the evaporation of sweat.

I couldn't tell you if 79% is particularly bad for Cyprus, but if you take a place like a rainforest the relative humidity rarely falls below 80%, with the high temperatures it wouldn't be too nice.

[cheeky_monkey]

A temperature-humidity index has been developed by the U.S. National Weather Service that gives a single numerical value in the general range of 70 to 80 reflecting the outdoor atmospheric conditions of temperature and humidity as a measure of comfort (or discomfort) during warm weather. The temperature-humidity index, I_TH, is defined as follows: I_TH=0.4 (dry-bulb thermometer temperature F + wet-bulb thermometer temperature F) + 15. When the index is 70 most people feel comfortable; at 75 about half the population is uncomfortable; at 80 most are uncomfortable.

yes the humidex index is a bit like windchill in reverse it adds humidty into the equation to give you the real feel temperature..for example 2 weeks ago the temp in Toronto was +33C but the with the humidex the real feel was +42c.

[SP1986]

In absolute terms it's kg of water to kg of air.

Normally in UK, we see around 0.0050kg/water to every kg of air.

In humid conditions it can be as much 0.00100kg/water to kg/air.

Doesnt sound much but it is..

[Terminal Moraine]

To answer your original question, a temperature of 27 c and relative humidity of 79% will feel decidedly sticky, you would need a relative humidity around 45%-50% at that temperature for it to feel comfortable.

[winterfreak]

To answer your original question, a temperature of 27 c and relative humidity of 79% will feel decidedly sticky, you would need a relative humidity around 45%-50% at that temperature for it to feel comfortable.

Thanks Terminal, an idea of what to expect then...Not very eco friendly but we'll have the A/C on then......

[ZONE 51]

How It Works- the-how stuff works-website

check this out - great site , i have searched Humidity for you and it should come up when you click link!

[Mesoscale]

Reminds me of being in the Yucatan Peninsula, Mexico. by the coast the humidity was around 89% but once you went in land the humidity went well over 90% probably more like 95/6%, it was absolutley horrible and the temperature was in the low 30s on the coast and in land was 35C+ it wasn't so much the temperature that got you (ive been to las vegas in mid summer now that is HOT! 45c on one day it was like a furnace during my 4 days there it didn't get below 40C in the day and just about got to 30c at night). but what gets you is just how uncomfortable it feels, your soaked etc. In cyprus its surrounded by water so I am guessing that it will moderate how it feels, my guess is that it will basically feel like a hot british day.

[knocker]

As someone has already mentioned what you are really talking about is the heat index. This is the best indicator. There was a very short thread on this a while ago.

http://forum.netweather.tv/topic/69022-heat-index/

[nikkirevo]

I'm getting to grips with using all the charts and am able to forecast most weather types. How do you forecast cloud though? What is the best chart type to use?

[SP1986]

I'm getting to grips with using all the charts and am able to forecast most weather types. How do you forecast cloud though? What is the best chart type to use?

I'm not sure whether the Net-weather charts have cloud forecasts but for cloud I used this one:

http://www.wetterzentrale.de/topkarten/fsavneur.html

In the top row of the menu you will find something called 'Mittl Wolken', this is the cloud amounts, the charts itself is fairly easy to read. (The thick green lines are airmass indicators measured as DAM (decameters)