That’s true, HomeKit does provide some support for temperature and humidity - thanks for the correction @vreihen. I should not have said it doesn’t “support outdoor weather parameters” because HomeKit doesn’t care if your T/RH sensor is indoors or out. What I should have said is that HomeKit does not currently include the concept of a weather station, nor any parameters a weather station measures other than temperature & humidity. The T & RH services are grouped with HVAC stuff (thermostats, heaters, coolers, fans, filters, etc).
More importantly, the other issue is that HomeKit support is limited to viewing T & RH values in the Home app. So (unless something’s changed recently), you can SEE the values in your Home app, but you can’t USE those values to create automations or do much else because they are not considered “triggers” by HomeKit or the Home app. If that’s not true, please correct me.
Regardless of all this, we still very much intend to support HomeKit! As I’ve explained previously, the current Hub was supposed to support it. It DID support it when we first designed it, but Apple changed the rules (and dramatically increased the hardware requirements) before we could finish the implementation. That hardware, even though it includes the special Apple MFI authentication coprocessor, no longer has enough oomph to run the HomeKit code. Our friends at Netatmo have a similar story (though it looks like theirs was even more frustrating than ours!).
I’m sorry if it sounds like I’m making excuses - I guess I am! 
But we are pressing forward!! The Pro Hub, which continues to be delayed for a number of different issues, has the extra processing and storage power (along with the MFI coprocessor) that it needs to support HomeKit. So, unless Apple moves the goal posts again, the Pro Hub will be able to support HomeKit. We have even completed a proof-of-concept with a prototype Pro Hub where the Tempest Hub could control a HomeKit light bulb (it was an exciting moment!).
Thanks for your understanding and patience!