There have been a couple of earlier experimental maps on the Wepoco site,  the first in 2007 was featured in the first Google Developer Day.  All have used rainfall estimates for Africa based on satellite observations.

Repository  - http://code.google.com/p/wepoco-web/source/checkout

Google App Engine site - http://wepoco-map.appspot.com Now available at http://map.wepoco.com