Abstract
In this paper, Hidden Markov Models (HMMs) are used to study the evolution of sunspots and to develop a model that can be used to predict the McIntosh class and the sunspot area for the sunspot under investigation for the next 24 hours. The testing results show accuracy in the prediction of next-day area and McIntosh classification reaching up to 71% and 60% respectively, when studied on the period from 18/08/1996 till 31/03/2006.