Australian Open Heat Stress Scale

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JT Smith
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Watching the Australian Open and they use a heat stress rating to protect the players. I've searched for the details of how it is calculated without success. Anyone know the formula that they use? Just curious.
 
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Note that both of these ignore wind speed!
Here is one from the USA National Weather Service:
(https://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml)


The Heat Index Equation

The computation of the heat index is a refinement of a result obtained by multiple regression analysis carried out by Lans P. Rothfusz and described in a 1990 National Weather Service (NWS) Technical Attachment (SR 90-23). The regression equation of Rothfusz is
HI = -42.379 + 2.04901523*T + 10.14333127*RH - .22475541*T*RH - .00683783*T*T - .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH - .00000199*T*T*RH*RH
where T is temperature in degrees F and RH is relative humidity in percent. HI is the heat index expressed as an apparent temperature in degrees F.
​

Just from personal experience, Sun loading adds to the effect.

Here is a different one from the NATIONAL CENTERS FOR ENVIRONMENTAL INFORMATION:
(https://www.ncdc.noaa.gov/societal-impacts/heat-stress/)


Defining a Heat Stress Index

When both temperature and humidity are high, humans can experience considerable heat stress. In the U.S., extreme heat may have greater impact on human health (Kalkstein and Davis 1989), especially among the elderly (Changnon et al. 1996), than any other type of severe weather. The combined effects of temperature and humidity cannot be directly measured but can be assessed by calculation of an "apparent temperature" (A). Ignoring wind effects, one can estimate apparent temperature as A (°C) = -1.3 + 0.92T + 2.2e, where T is ambient air temperature (°C) and e is water vapor pressure (kPa) (Steadman 1984).
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(above respectively found with:
https://www.google.com/search?&q=heat+index+formula
https://www.google.com/search?&q=human+heat+stress+index)

Cheers,
Tom
 
Thanks for taking the time to reply.

I know there are other examples of a heat index. I was curious specifically about the Australian Open's new index which, near as I can tell, is some sort of secret. Why they would be unwilling to explain how they determine the index value I can't say I understand. But it does take into account wind speed and radiant heat.