The H-IIA rocket will blast off from a southern Japanese island at 3:37 am tomorrow, (1837 GMT today) with the Global Precipitation Measurement (GPM) core observatory aboard, the Japan Aerospace Exploration Agency (JAXA) said.
The satellite, jointly developed by Japan and the United States, is designed to collect data from several other satellites in orbit and add that to its own measurements to build up a detailed picture of precipitation around the planet.
Weather forecasters say that with a more detailed and complete map of rain they will be better able to predict extreme events such as typhoons and floods.
"From the ISS, I wish for the success of the launch," he wrote.