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NEA provides API's for readings of temperature, humidity, precipitation and wind conditions at up to one-minute intervals. The data is provided at weather-station level.
The API descriptions can be found on https://data.gov.sg For rainfall: https://data.gov.sg/dataset/realtime-weather-readings?resource_id=8bd37e06-cdd7-4ca4-9ad8-5754eb70a33d
Data can only be requested one day at at time, for example: https://api.data.gov.sg/v1/environment/rainfall?date=2018-07-26