The ObserverIP weather station module (mine came in the Ambient Weather WS-1200-IP unit, but also found in other kits) doesn’t have an API to access the weather data directly. This Python script is a quick example on how to screen scrape the data. Sources cited in the code.
Update: This method may cause your ObserverIP to crash! I have another method outlined here: http://obrienlabs.net/redirecting-weather-station-data-from-observerip/