Heat Index: Bulb
Wet Bulb, WBGT & OSHA Safety
Only for iPhone
Free · In‑App Purchases · Designed for iPhone. Not verified for macOS.
iPhone
New: see how hot your game is. Every college football, NFL and Premier League kickoff this week, ranked by heat index — plus the hottest cities on Earth today.
Heat Index answers one question: will I overheat? It shows the heat index and the WBGT where you are standing, hour by hour, and warns you before the day crosses your line.
Every number is computed on your phone from Apple Weather data — temperature, humidity, wind, cloud cover and the sun's exact angle at your coordinates. No account, no ads, no analytics. Your location goes to Apple's WeatherKit and nowhere else.
TWO NUMBERS, ONE TAP APART
The National Weather Service says it plainly: for day-to-day activities the heat index serves you well; if you work outside in full sun, use the WBGT. Heat Index gives you both. A picker at the top chooses which one you are reading; the whole screen follows it.
Both flag onto the same five names — Comfortable, Caution, Extreme caution, Danger, Extreme danger — each on its own published scale: the NWS chart steps for the heat index, the US military flag conditions (82 / 85 / 88 / 90 °F) for WBGT.
TODAY, FREE
• The heat index or the estimated WBGT, large, with its flag and the published guidance for it
• A 24-hour timeline from midnight — drag to any hour and every card follows
• Why is it Danger? — whether humidity, sun, wind or plain heat is driving it
• Nine tiles: air temp, heat index, wet bulb, humidity, dew point, wind, UV, sunrise, sunset
• The safest window today, and the next hours at a glance
• A plain-English explainer behind every ?, including the 35 °C survivability limit
THE WEEK AHEAD
• Your metric charted hour by hour for seven days
• Tap any day for its peak, its hours at or above Danger, and its best working window
• A warning when dangerous days stack up
HEAT ALERTS
• A notification 30 minutes before conditions cross the line you set
• Two conditions, each with its own switch and threshold: WBGT and heat index
• Each fires on the way up only, so a long hot afternoon warns you once, not every hour
• Morning brief: the peak of the day ahead and the hour it lands
• Limit them to your shift hours and your working days
• Watch up to five sites at once, whether or not you are standing on them
• Scheduled on your device from the forecast — no push server, no account
SAVED SITES
Search an address or drop a pin. Named for the town, never the street, and renamable.
WIDGETS
Right Now, Today's Shape and a lock screen set. Long-press any of them to pick the number and the place.
ASK SIRI
"Is it safe to work outside in Heat Index", "What's the WBGT in Heat Index".
THE MATH, AND HOW IT WAS CHECKED
• Heat index: the official NWS Rothfusz regression, within 0.92 °F of the NWS chart — never Apple's proprietary "feels like"
• Wet bulb: Stull (2011), checked against an exact thermodynamic solve
• Solar load: NOAA solar position with cloud attenuation, scored against measurements
• WBGT: solved by energy balance, stated in full sun, with the shade figure under it
Today is free at your current location. Pro adds the week ahead, heat alerts, widgets and saved sites.
Weather data provided by Apple Weather.
Heat Index is a planning tool, not a compliance instrument. Every figure is an estimate computed from forecast weather at your coordinates, not measured on your site, and an instrument on the job will read differently. It is not a substitute for your employer's heat illness prevention program or your safety officer's judgement.
Payment will be charged to your Apple ID account at the confirmation of purchase. The subscription automatically renews unless it is canceled at least 24 hours before the end of the current period. Your account will be charged for renewal within 24 hours before the end of the current period. You can manage and cancel your subscriptions by going to your App Store account settings after purchase. Cancellation of the current active subscription period is not allowed.
Terms of Use: https://pattammaro.com/heat-index/terms-of-use
Privacy Policy: https://pattammaro.com/heat-index/privacy-policy
Ratings & Reviews
- This app hasn’t received enough ratings or reviews to display an overview.
THE HEAT LEADERBOARDS
Every kickoff on this week's schedule, ranked by heat index. College football, the NFL and the Premier League — see where your game sits in the slate, and who is playing in the worst of it.
• The week's full schedule for all three leagues, each game with its forecast heat index at kickoff
• Tap a matchup for the card: the figure, the band it falls in, the venue's own local kickoff time, and a link to ESPN
• A game's number freezes at kickoff, so one already played keeps the heat it was played in
• The 177 hottest cities on Earth, ranked on today's local peak — with your own location slotted in at its rank
• Share any top ten
Rankings rebuild through the day, so the slate keeps up as the forecast moves.
The developer, Patrick Tammaro, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Linked to You
The following data may be collected but it is not linked to your identity:
- Identifiers
- Usage Data
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Patrick Tammaro
- Size
- 38.1 MB
- Category
- Weather
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later. - Mac
Requires macOS 14.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
English and 10 more
- English, Dutch, French, German, Italian, Japanese, Korean, Portuguese, Simplified Chinese, Spanish, Traditional Chinese
- Age Rating
4+
- 4+
- In-App Purchases
Yes
- Pro $29.99
- Pro $5.99
- Copyright
- © 2026 Cardiac Apps LLC