HN users may mostly know Wet Bulb Temperatures through Chapter 1 of 'Ministry for the Future' set in India. Well, the topic was close to home, so I built something for myself.
Where I live, the difficult dry summer heat usually peaked in May/June, but now seems to extend into September.
I grew up with 100F / 37C summers, sometimes reaching 110F / 43C, and temperatures around 86F / 30C felt familiar and manageable.
So it’s confusing when the same 86F / 30C now feels so much warmer.
May/June were hot but dry, so sweat didn't pool and stick... Now Jul through Sep the air often feels muggy, thick like a soup with moisture, holding heat well into the evening.
Thats really when it clicked for me what WBGT/Wet-Bulb Temperatures was about:
Wet Bulb Temperature is not really a measure of 'hot' air like Heat Index. It’s a measure of how 'cool' my body can get by sweating.
Both are temperatures, but from different math, about very different things, and sending very different signals.
To make the signal more usable, I built *Wet Bulb Tracker*, an app that sends you automatic Notifications when wet-bulb conditions reach higher-risk levels, while telling you what the temperature risk level means. It’s to give the average home user a heads up.
I spent a lot of time iterating on the UI in Figma, trying to make WBGT look and feel more directly and immediately related to health, less like another Temperature. And to make it understandable at a glance.
The app leads with the temperature, but uses five color-coded risk levels to give them meaning based on many published global institutional categories - from OSHA, Military, to Govt Ministries.
There's also an hourly timeline (with scrubbing), with written guidance on staying cool for each level. The day’s weather on the side as a background essential.
For optional extra convenience, 6-day forecasts help you plan the week, and Widgets and a Watch App also keep the timeline visible.
The math model implementation I couldn't have built without AI. Claude Code was particularly good, building a hybrid Liljegren & Dimiceli/Piltz system that each provide different parts of the main WBGT equation, rendered in Swift.
I'm interested in whether the way I've communicated WBGT actually makes it stand out from regular heat Index.
What would make this more useful as an everyday summer or travel tool?
"How cool my body can get by sweating" is the best explanation of wet bulb I've seen, lead with that. And for travel, warn me the night before, not at 2pm when im already outside.
Hey...glad the Wet Bulb framing worked for you! It took me a while to distill it for myself, from reading about in the press and literature.
I did in fact, have alerts set up for the day before, in early versions.
In practice though, the exact times were a bit shifty because weather forecasts update constantly. (I discovered that even the weather record for past hours updates after the time has passed, as the data flows in asynchronously)
So firing notifications in advance became about a balance between accuracy, annoyance and too much info, plus the apps scheduling them with iOS.
Eventually I figured showing a timeline for the day in the app and widget made more sense, and alerts firing as they happened.
Thanks for the feedback. I'll keep looking for a balance between usability vs technical constraints for this.
Where I live, the difficult dry summer heat usually peaked in May/June, but now seems to extend into September.
I grew up with 100F / 37C summers, sometimes reaching 110F / 43C, and temperatures around 86F / 30C felt familiar and manageable. So it’s confusing when the same 86F / 30C now feels so much warmer.
May/June were hot but dry, so sweat didn't pool and stick... Now Jul through Sep the air often feels muggy, thick like a soup with moisture, holding heat well into the evening.
Thats really when it clicked for me what WBGT/Wet-Bulb Temperatures was about: Wet Bulb Temperature is not really a measure of 'hot' air like Heat Index. It’s a measure of how 'cool' my body can get by sweating.
Both are temperatures, but from different math, about very different things, and sending very different signals.
To make the signal more usable, I built *Wet Bulb Tracker*, an app that sends you automatic Notifications when wet-bulb conditions reach higher-risk levels, while telling you what the temperature risk level means. It’s to give the average home user a heads up.
I spent a lot of time iterating on the UI in Figma, trying to make WBGT look and feel more directly and immediately related to health, less like another Temperature. And to make it understandable at a glance.
The app leads with the temperature, but uses five color-coded risk levels to give them meaning based on many published global institutional categories - from OSHA, Military, to Govt Ministries. There's also an hourly timeline (with scrubbing), with written guidance on staying cool for each level. The day’s weather on the side as a background essential.
For optional extra convenience, 6-day forecasts help you plan the week, and Widgets and a Watch App also keep the timeline visible.
The math model implementation I couldn't have built without AI. Claude Code was particularly good, building a hybrid Liljegren & Dimiceli/Piltz system that each provide different parts of the main WBGT equation, rendered in Swift.
I'm interested in whether the way I've communicated WBGT actually makes it stand out from regular heat Index.
What would make this more useful as an everyday summer or travel tool?
Check out the app on the App Store: https://apps.apple.com/in/app/wet-bulb-temperature-tracker/i...
wet-bulb-temperature.com
"How cool my body can get by sweating" is the best explanation of wet bulb I've seen, lead with that. And for travel, warn me the night before, not at 2pm when im already outside.
Hey...glad the Wet Bulb framing worked for you! It took me a while to distill it for myself, from reading about in the press and literature.
I did in fact, have alerts set up for the day before, in early versions. In practice though, the exact times were a bit shifty because weather forecasts update constantly. (I discovered that even the weather record for past hours updates after the time has passed, as the data flows in asynchronously)
So firing notifications in advance became about a balance between accuracy, annoyance and too much info, plus the apps scheduling them with iOS.
Eventually I figured showing a timeline for the day in the app and widget made more sense, and alerts firing as they happened. Thanks for the feedback. I'll keep looking for a balance between usability vs technical constraints for this.