From north to south on the territory of Bulgaria there are alternate temperate continental climate and transitional climate, while in the south an impact of the Mediterranean climate is felt. The average annual air temperature is 10.5 degrees centigrade (51 F). Altitude differences determine the vertical zoning of the climate. To the east there is an influence by the Black Sea – the summers are cooler and autumns - warmer and longer. The combination of the course of air and sea water temperatures with average values above 18 degrees C (65 F) is favorable to seaside vacationing in the period from May till early October. The soft transitional Mediterranean climate and the fertile soils are very suitable for growing the century-famed Bulgarian attar-yielding rose – a valuable raw material for perfumery, medical and food, wine and tobacco industries.