Edit the HTML page and remove the following lines:
<input id="rad_dew2" type="radio" name="rad_dew" value="app" checked onclick="doDew(this);">
<label id="lab_dew2" for="rad_dew2">Apparent</label>
and
<input id="rad_dew5" type="radio" name="rad_dew" value="hum" onclick="doDew(this);">
<label id="lab_dew5" for="rad_dew5">Humidex</label>
Then change:
<input id="rad_dew1" type="radio" name="rad_dew" value="dew" onclick="doDew(this);">
to
<input id="rad_dew1" type="radio" name="rad_dew" value="dew" checked onclick="doDew(this);">
Edit gauges.js and around line 181 change:
g_dew.selected = 'app';
to
g_dew.selected = 'dew';
Done.