Convert openweathermap dewpoint from kelvin to celcius (#51893)

Co-authored-by: Martin Hjelmare <marhje52@gmail.com>
Co-authored-by: Franck Nijhof <git@frenck.dev>

homeassistant/components/openweathermap/weather_update_coordinator.py

@@ -18,6 +18,7 @@ from homeassistant.components.weather import (
     ATTR_FORECAST_WIND_BEARING,
     ATTR_FORECAST_WIND_SPEED,
 )
+from homeassistant.const import TEMP_CELSIUS
 from homeassistant.helpers import sun
 from homeassistant.helpers.update_coordinator import DataUpdateCoordinator, UpdateFailed
 from homeassistant.util import dt
@@ -179,10 +180,10 @@ class WeatherUpdateCoordinator(DataUpdateCoordinator):
 
         return forecast
 
-    @staticmethod
-    def _fmt_dewpoint(dewpoint):
+    def _fmt_dewpoint(self, dewpoint):
         if dewpoint is not None:
-            return round(dewpoint / 100, 1)
+            dewpoint = dewpoint - 273.15
+            return round(self.hass.config.units.temperature(dewpoint, TEMP_CELSIUS), 1)
         return None
 
     @staticmethod

tests/components/openweathermap/test_config_flow.py

@@ -187,6 +187,7 @@ def _create_mocked_owm(is_api_online: bool):
     weather.snow.return_value = []
     weather.detailed_status.return_value = "status"
     weather.weather_code = 803
+    weather.dewpoint = 10
 
     mocked_owm.weather_at_coords.return_value.weather = weather