How can prediction or forecasting be permissible (halal) and free from speculation and fortune-telling?

A Muslim must believe that Allah alone knows the Unseen. Whoever claims knowledge of the Unseen or attributes it to someone else has exited Islam and disbelieved in the Quran and Sunnah (definition). Allah Almighty says: (Say: None in the heavens and earth knows the unseen except Allah). If prediction implies claiming knowledge of the Unseen, then it is forbidden. However, if it is merely a prediction based on apparent signs and indications, such as expecting rain upon seeing clouds, then there is no harm in it.