How To Retrieve Weather Forecast From OpenWeatherMap For A Given Local Date and Time expressed using Local Time Zone?

OpenWeatherMap API provides a free 5 day weather forecast service with forecast reports at 3 hour intervals per day for a given city.

daily_forecast_data = [UTC date:12:00, UTC date:03:00, UTC date:06:00, UTC date:09:00, UTC date:12:00, UTC date:15:00, UTC date:18:00, UTC date:21:00]

If the requester is in Sydney the UTC time offset is +10:00 hrs.

So assuming the following 5 day forecast time window:

start = 2021-09-03T12:00:00:00:00
end = 2021-09-08T12:00:00:00:00

If I am providing an API endpoint weather server that accepts a city and ISO8601 date string for that city’s local timezone, how do I retrieve the correct weather forecast from OpenWeatherMap for that date and time for that city?

API Sydney Example GET /weather/sydney/?when=2021-09-06T15:00+10:00

This represents querying a forecast for 2021-09-06 3pm in Sydney.

The OpenWeatherMap 5 day forecast for a city gives a response with 3hour reference timestamps reported in UTC for those 5 days.

Would I have to filter the openweathermap resultset for 2021-09-06 and then convert each 3 hour slot’s, reference timestamp to local time to find the closest match to T15:00+10:00?

I have tried using pyorm Python library to facilitate making the request to openweathermap.org:

    owm = OWM("<API KEY>")
    mgr = owm.weather_manager()
    three_h_forecaster = mgr.forecast_at_place("Sydney,AUS", "3h")
    day_iso = "2021-09-06T15:00+10:00:00"

    weather = three_h_forecaster.get_weather_at(day_iso)
    print(f"WEATHER FOR Sydney 3H starts := {three_h_forecaster.when_starts('iso')}")
    print(f"WEATHER FOR Sydney 3H ends := {three_h_forecaster.when_ends('iso')}")
    print(f"Weather for {day_iso} is :: \n{json.dumps(weather.to_dict(), indent=4)}")
    print(f"Weather reference time is: {weather.reference_time('iso')}")

WEATHER FOR Sydney 3H starts := 2021-09-03 15:00:00+00:00
WEATHER FOR Sydney 3H ends := 2021-09-08 12:00:00+00:00
Weather for 2021-09-06T15:00+10:00:00 is :: 
{
    "reference_time": 1630908000,
    "sunset_time": null,
    "sunrise_time": null,
    "clouds": 32,
    "rain": {},
    "snow": {},
    "wind": {
        "speed": 10.42,
        "deg": 193,
        "gust": 14.76
    },
    "humidity": 53,
    "pressure": {
        "press": 1027,
        "sea_level": 1027
    },
    "temperature": {
        "temp": 287.64,
        "temp_kf": 0,
        "temp_max": 287.64,
        "temp_min": 287.64,
        "feels_like": 286.53
    },
    "status": "Clouds",
    "detailed_status": "scattered clouds",
    "weather_code": 802,
    "weather_icon_name": "03d",
    "visibility_distance": 10000,
    "dewpoint": null,
    "humidex": null,
    "heat_index": null,
    "utc_offset": null,
    "uvi": null,
    "precipitation_probability": 0.02
}
Weather reference time is: 2021-09-06 06:00:00+00:00

Am I using this correct? I notice that the reference time reported is 2021-09-06 06:00:00+00:00…

[csparpa]

Hi @dcs3spp I would advice to use the OneCall features so that you get fresh data and no backwards-compatibility issues in the long run . And bonus feature: you get forecasted weather with HOURLY granularity (you’re aiming for 3 hours now)

Apart from that, I guess the correct process is:

1. you accept local time as a parameter (eg. Sidney timezone) to your endpoint
2. you turn that into UTC and extract the related UNIX epoch
3. you can pass that UNIX epoch to the utility function: pyowm.utils.weather.find_closest_weather

This is a working example that retrieves forecasted weather on Sidney at 15 hours after you run the code:

from pyowm.owm import OWM
from pyowm.utils.weather import find_closest_weather
from datetime import datetime, timedelta

owm = OWM('YOUR_API_KEY')

gcm = owm.geocoding_manager()
mgr = owm.weather_manager()

# This should be the epoch resulting from turning your endpoint's parameter to UTC...
target_time = int((datetime.utcnow() + timedelta(hours=15)).timestamp())  # UTC epoch for: now + 15 hours

# geocode Sidney
sidney = gcm.geocode('Sidney', 'AU')[0]

# call the API
response = mgr.one_call(lat=sidney.lat, lon=sidney.lon)  # OneCall object containing current and forecast weather on Sidney

# retrieve the forecasted weather that is closest to your target epoch
weathers = response.forecast_hourly
closest_weather = find_closest_weather(weathers, target_time)  # this is what you're looking for!

Is this of any help ?

[csparpa]

Normally you don’t need to specify any timezone when you invoke the OneCall API for a city

As far as I konw, OWM does not provide any timezone detail when looking up for city IDs or geocoding

Nevertheless, Python libraries do exist for this purpose (eg: geopy)