Complex sentence: In fall there is a steady increase in Medicane formation in the western Mediterranean region whereas it decreases in January, in the Ionian region it is vice versa and Medicanes are much less frequent in fall than in January or February.
Split into simpler sentences: In fall there is a steady increase in Medicane formation in the western Mediterranean region and in January it decreases. In the Ionian region Medicanes are less frequent in fall than in January or February.