Fire danger calculator

Fire danger calculator at http://zfpa.co.za/fdi.html (see online calculator).

Both low RH and high wind speeds dry vegetation and result in higher probability of fires.
a) I have divided the wind speed by RH for each day and constructed a formula to give a "drying index" (black curve). Looking at the graph one can see where there could be a strong cumulative effect (many days one after the other where winspeed/RH is high). Above 0 spells danger for the "Drying Index".
b) I also used the Angstrom Index in another formula and calibrated, etc. Above 0 spells danger for my combined "Dryness Linked Fire Index".
Details:
1) The Angstrom Index (a well known index) is evaluated at midday, so I have used maximum temperatures for the day from the 7 day weather forecast. An RH of 0.5 (50%) and a wind speed of 11 km/hour are regarded by me as average (not safe or dangerous). Since 11/0.5=22, one can subtract 22 from windspeed/RH to centre this index at 0, so windspeed/Rh - 22 is centred at 0 (the intention is that above zero is favourable for fires and below is not).
2) The well known Angstrom Index formula is
Ai=RH/20 + (27-T)/10 and a value for Ai greater than 3 is unfavourable for fires and a value less than 3 is favourable for fires (I have seen slightly different opinions on these figures). Anyhow, these Angstrom index figures are a bit confusing, so I use my own formula (100)(1/Ai) - 33.333 and then from 0 upwards is favourable for fires and a value below 0 is unfavourable.
1) My dryness index is [ (windspeed/RH) - 22 ]/3 (black curve)
2) My combined Dryness Linked Fire Index formula is
100(1/Ai) - 33.333 + [ (windspeed/RH) - 22 ]/3 (red curve).