Nowcasting of harmful algal blooms is important both for the public and for environmental management purposes. In the Baltic Sea summer blooms of nitrogen-fixing cyanobacteria are regular phenomena but the past years intense and widespread blooms have caused major environmental concern due to its nuisance, increased nitrogen input and toxicity. The Swedish Meteorological and Hydrological Institute have developed a monitoring application that use satellite data to detect blooms and that assembles essential sources of information at one website. A supervised classifications algorithm has been applied to NOAA-AVHRR data during 1997-2006 and the dataset collected has been evaluated and analyzed. Subsequently, definitions of normalized bloom duration, extent and intensity have been developed to enable comparison between different years. Results suggest that the most intense blooms during 1997-2006 were recorded in 2006, while both 2005 and 2006 had the longest duration. The largest extent was noted in 1998. The experience from the 10 years of monitoring has shown that the combination of satellite imagery, observations, forecasts and tools assembled at one website, is a powerful nowcasting tool for monitoring and prediction of cyanobacterial blooms.