Topic: Humidex formula .

[Total]

Hi : I'm using this formula now

 // JavaScript Document
   var T = ^vxv007^ ;
   var H = ^vxv005^ ;
   var t = 7.5*T/(237.7 + T);
   var et = Math.pow(10,t);
   var e = 6.112*et*(H/100);
   var humidex = T + (5 / 9) * (e - 10);
   if (humidex < T)
   { humidex = T;
   }
   document.write(Math.ceil(humidex));

But it is always off on the humidex that is reported at my location .  Ideas . could someone help with making  the wikipedia formula ? thanks
https://en.wikipedia.org/wiki/Humidex

[Jáchym]

What temperature units is your T in

[Total]

T is in Celsius .

[Jáchym]

I cannot guarantee, but try this:

Code: [Select]

var T = ^vxv007^ ;
var H = ^vxv005^ ;
var D = ((Math.pow((H/100), 0.125))*(112+0.9*T)+(0.1*T)-112);
var temporary = 5471.7530 * (1/273.16 - 1/(D-273.15));
var temporary2 = 6.11*Math.log(temporary)-10;
result = T + 0.555 * temporary2;
document.write(Math.ceil(result ));

[Total]

Will do . thanks

[ericfynne]

https://github.com/eswak/humidex/blob/master/humidex.js

[Jáchym]

Oh I see a problem, sorry, the third line should be like this:

var temporary = 5471.7530 * (1/273.16 - 1/(D+273.15));

[Total]

Tried it , but the values are really low ..

[Total]

The humidex now is below the temp outside . http://www.strutherslakeweather.ca/  , up at the top . thanks .

[Jáchym]

I dont know, in my template I use the formula for apparent temperature. It is in my opinion the best parameter because:

- windchill - takes into account temperature and the wind speed cooling effect
- humidex - takes into account temperature and the humidity warming effect
- feels like (apparent) temperature - takes into account temperature, wind speed and humidity. For high Ts, it usually is higher than the T, though if it is windy it doesnt have to be. At low Ts, it is usually either equal or much lower, depending on wind speed

[Total]

thanks for this . So this formula is for the apparent temperature ? Correct .

[Jáchym]

No, for that I use this:

t = Temperature in C
hum = Humidity in %
w = wind speed in km/h

Code: [Select]

function feeltemp(T, hum, w){
t = eval(T);
rh = eval(hum);
w = eval(w/3.6);
e = (rh/100)*6.105*Math.pow(2.71828, ((17.27*t)/(237.7+t)));
at = Math.round((t + 0.33*e-0.7*w-4)*10)/10;
at = at.toFixed(1);
                return at;
}
So for example this would show you the apparent T:

apparent = feeltemp(25,50,15);
alert(apparent);

[ericfynne]

Have you tried the code from the link I posted? It seems to be correct.

Eric

[Total]

Have you tried the code from the link I posted? It seems to be correct.

Eric

I looked at it but don't know how to make it work with my web page ...

'use strict';

/*
 * @param {t} : The temperature in °C
 * @param {h} : The air humidity in % (0 <= h <= 1)
 * @returns : the humidex in °C
 */
module.exports = function humidex (t, h) {
  var dewPoint = Math.pow(h, 1 / * (112 + 0.9 * t) + 0.1 * t - 112;
  var expIndex = 5417.753 * ((1 / 273.16) - (1 / (dewPoint + 273.16)));
  return t + 0.5555 * (6.11 * Math.exp(expIndex) - 10);
};


off my web page

....... <font face="Arial">Humidex (feels like):</font> <font
      face="Arial">
      <script language="javascript">



// JavaScript Document
  var T = ^vxv007^ ;
  var H = ^vxv005^ ;
  var D = ((Math.pow((H/100), 0.125))*(112+0.9*T)+(0.1*T)-112);
  var temporary = 5471.7530 * (1/273.16 - 1/(D+273.16));
  var temporary2 = 6.11*Math.log(temporary)-10;
  result = T + 0.555 * temporary2;
  if (result < T)
     { result = T;
   }
document.write(Math.ceil(result ));
   </script>°C </font>

[ericfynne]

Instead of your original:

// JavaScript Document
  var T = ^vxv007^ ;
  var H = ^vxv005^ ;
  var D = ((Math.pow((H/100), 0.125))*(112+0.9*T)+(0.1*T)-112);
  var temporary = 5471.7530 * (1/273.16 - 1/(D+273.16));
  var temporary2 = 6.11*Math.log(temporary)-10;
  result = T + 0.555 * temporary2;
  if (result < T)
     { result = T;
   }
document.write(Math.ceil(result ));
   </script>°C </font>

try

// JavaScript Document
  var T = ^vxv007^ ;
  var H = ^vxv005^ ;
  var dewPoint = Math.pow(H, 1 / 8 ) * (112 + 0.9 * T) + 0.1 * T - 112;
  var expIndex = 5417.753 * ((1 / 273.16) - (1 / (dewPoint + 273.16)));
  result = T + 0.5555 * (6.11 * Math.exp(expIndex) - 10);
  if (result < T)
     { result = T;
   }
document.write(Math.ceil(result ));
   </script>°C </font>

The effective differences between what you had and this are small, but important.

[Total]

Will try it and reply back .thanks again .. 

[Total]

Will try it and reply back .thanks again .. 

Something is wrong ..  Humidex (feels like): 579°C   

[Jáchym]

Did you try my feels like formula?

[Total]

Does this look right ?  for the feels like temp ?
<script language="javascript">

// JavaScript Document
// t = Temperature in C
// hum = Humidity in %
// w = wind speed in km/h (M = mph)
   var t = ^vxv007^ ;
   var hum = ^vxv005^ ;
   var M = ^vxv002^ ; 
   var w = M * 1.60934 ;

 function feeltemp(T, hum, w){
      t = eval(T);
      rh = eval(hum);
      w = eval(w/3.6);
      e = (rh/100)*6.105*Math.pow(2.71828, ((17.27*t)/(237.7+t)));
      at = Math.round((t + 0.33*e-0.7*w-4)*10)/10;
      at = at.toFixed(1);
                return at;
                   }
                document.write(Math.ceil(at));
   </script>°C </font> 

[ericfynne]

Something is wrong ..  Humidex (feels like): 579°C

The spec for the function is wrong, it's expecting humidity as a fraction of 1, not as a percentage (like your original code).

So this line:

var dewPoint = Math.pow((H, 1 / 8 ) * (112 + 0.9 * T) + 0.1 * T - 112;

needs to be

var dewPoint = Math.pow((H/100), 1 / 8 ) * (112 + 0.9 * T) + 0.1 * T - 112;

I think that means that the only actual difference between the code from that site and the code Jachym supplied, is that it needs to use Math.exp rather than Math.log in the final calculation.

[Total]

Something is wrong ..  Humidex (feels like): 579°C

The spec for the function is wrong, it's expecting humidity as a fraction of 1, not as a percentage (like your original code).

So this line:

var dewPoint = Math.pow((H, 1 / 8 ) * (112 + 0.9 * T) + 0.1 * T - 112;

needs to be

var dewPoint = Math.pow((H/100), 1 / 8 ) * (112 + 0.9 * T) + 0.1 * T - 112;

I think that means that the only actual difference between the code from that site and the code Jachym supplied, is that it needs to use Math.exp rather than Math.log in the final calculation.

thanks - that works now . I'm learning all the time .

Now if I can get Jachym's feel like code to read on my site .

[Jáchym]

You need to run the function and pass the parameters to it, so like this for example:

<script>
var t = ^vxv007^ ;
var hum = ^vxv005^ ;
var M = ^vxv002^ ; 
var w = M * 1.60934 ;

feelsLike = feeltemp(t,hum,w);
document.write(feelsLike);

function feeltemp(T, hum, w){
      t = eval(T);
      rh = eval(hum);
      w = eval(w/3.6);
      e = (rh/100)*6.105*Math.pow(2.71828, ((17.27*t)/(237.7+t)));
      at = Math.round((t + 0.33*e-0.7*w-4)*10)/10;
      at = at.toFixed(1);
      return at;
   }
   </script>

[Total]

You need to run the function and pass the parameters to it, so like this for example:

<script>
var t = ^vxv007^ ;
var hum = ^vxv005^ ;
var M = ^vxv002^ ; 
var w = M * 1.60934 ;

feelsLike = feeltemp(t,hum,w);
document.write(feelsLike);

function feeltemp(T, hum, w){
      t = eval(T);
      rh = eval(hum);
      w = eval(w/3.6);
      e = (rh/100)*6.105*Math.pow(2.71828, ((17.27*t)/(237.7+t)));
      at = Math.round((t + 0.33*e-0.7*w-4)*10)/10;
      at = at.toFixed(1);
      return at;
   }
   </script>

So if I paste this into my wx.htx file all will work ? thanks

[Jáchym]

Im not sure, I mean I dont know which file you are talking about, the above script is the function to calculate it.

Just try it, but I dont know which page you are trying to insert it into, I just used what you posted above.

[Total]

Im not sure, I mean I dont know which file you are talking about, the above script is the function to calculate it.

Just try it, but I dont know which page you are trying to insert it into, I just used what you posted above.

thanks , and I appreciate your help . Is this Java ?