Transparency

Methodology You Can Audit

ClimaSafe computes WBGT with the peer-reviewed Liljegren (2008)model from live Open-Meteo weather, and validates that enginebit-for-bit against ECMWF’s reference library across 840 conditionsand its solar geometry against NREL’s Solar Position Algorithm. A safety number is only as good as its provenance, so here is all of ours.

Last updated July 9, 2026 · Live data refreshes every 15 min

The data pipeline

Every reading starts with real weather. ClimaSafe queriesOpen-Meteo at 59 points spread across the three islands, requesting air temperature, relative humidity, wind speed and direction, surface pressure, cloud cover, and three solar-radiation fields (direct, diffuse, and shortwave). A Cloudflare Worker caches the response for 15 minutes so the site stays fast and courteous to the upstream API. Land cover for surface context comes from theESA WorldCover 2021 dataset.

From weather to WBGT

The map does not fetch a WBGT number, it computes one, in your browser, for every point. It uses the Liljegren et al. (2008)energy-balance model, the method meteorological institutions use to derive WBGT from standard weather. The model solves two miniature physics problems: the steady-state temperature of a black globe absorbing sun, and the temperature of a wetted wick losing heat to evaporation and airflow. Those become the globe (Tg) and natural wet-bulb (Tnwb) terms, combined as 0.7 · Tnwb + 0.2 · Tg + 0.1 · Ta.

This matters because a common shortcut substitutes the ordinary (psychrometric) wet-bulb temperature for the natural one. That shortcut is only valid in shade and understates outdoor heat in sun, precisely the USVI case. ClimaSafe does the full physics instead.

The verification chain

Three links, each independently checkable:

Liljegren et al. (2008)

The peer-reviewed physical model, used operationally by national meteorological services.

doi:10.1080/15459620802310770

ECMWF thermofeel

Europe’s reference implementation, itself validated against Liljegren’s original C code.

oracle for 840 test cases

ClimaSafe’s engine

The browser implementation, checked against that oracle across the full tropical envelope.

max deviation 0.0000 °C

Solar geometry, which governs how much direct sun loads the globe, is validated separately against NREL’s Solar Position Algorithm (via pvlib) across 1,440 samples spanning five dates and all three islands. The worst-case impact of our solar approximation on the final WBGT is ±0.11°F, and just 0.03°F at peak midday sun. Interpolation, wind-vector, and color-binning math each carry their own automated test suites.

Re-audited on every change. The full suite, engine, interpolation, solar geometry, color binning, and a live-data sanity check, runs as npm run verify:all. When the numbers change, the proof runs again.

Honest limitations

We would rather you trust ClimaSafe because it is candid than because it is confident:

References & data sources

  1. Liljegren, J.C., et al. (2008). J. Occup. Environ. Hyg. doi:10.1080/15459620802310770
  2. Kong, Q., & Huber, M. (2022). Explicit Calculations of WBGT Compared With Approximations. Earth's Future. doi:10.1029/2021EF002334
  3. Reda, I., & Andreas, A. (2004). Solar Position Algorithm. NREL (via pvlib).
  4. Open-Meteo weather API, open-meteo.com. ESA WorldCover 2021, esa-worldcover.org.
  5. U.S. NWS WBGT, weather.gov/ict/WBGT. OSHA heat, osha.gov/heat-exposure.

Frequently asked questions

Where does ClimaSafe get its weather data?
From Open-Meteo, an open weather API, queried at 59 points across the three islands and cached for 15 minutes through a Cloudflare Worker. Inputs include temperature, humidity, wind, surface pressure, and direct, diffuse, and shortwave solar radiation.
How is the WBGT itself calculated?
With the Liljegren et al. (2008) energy-balance model, which solves the globe and natural wet-bulb temperatures from the weather inputs. ClimaSafe’s implementation is validated bit-for-bit against ECMWF’s reference library across 840 test conditions.
How accurate is the map between the 59 data points?
Values between points are inverse-distance interpolated, so the map is smooth but does not invent sub-kilometre detail. The underlying weather model resolves roughly 11 km, and true microclimates, a shaded ravine, a hot parking lot, can differ from the mapped value.
Where do the cloud cover and wind numbers come from?
From the Open-Meteo forecast model, interpolated to the location you select. They are shown as data in the analysis panel and they feed the WBGT physics directly: cloud cover reduces the solar load on the globe thermometer, and wind speed changes both the globe and natural wet-bulb terms. They are model values, not satellite or radar imagery.
Does ClimaSafe replace the National Weather Service?
No. ClimaSafe is a free educational tool for planning outdoor activity. Always follow official NWS/NOAA advisories and guidance from VITEMA and the VI Department of Health during heat events.