Hey this sounds like a cool project. It’s easy to write these rules based on the forecast for rain and/or humidity with Home Assistant. There are many free forecasting integrations like AccuWeather so you can take action based on what’s forecasted today or the next few days.
Let’s say you want to take additional action at 11 am if the forecast for that day is temp over 100F. I see there’s a Rachio integration so you should be able to let HA manually control your zones and then I’d also have it send you a push notification that it ran or didn’t.
There is also no reason you couldn’t ask HA to check the temp every hour with some local temp sensor you’ve got on the property, and then if the max at any point that way was above, say 100F, turn on the zones at 5 pm for a couple of minutes of supplemental watering.