 Milford Sound receives over 6,700 mm of the rainfall a year on average while barely 100 km away Alexandra in Central Otago receives only slightly greater than 300 mm annually, giving it a borderline oceanic/semi-arid climate.Air laden with water vapour from the ocean is pushed from the west in response to Earth’s rotation.This weather circulates the southern seas largely unimpeded by land until is reaches the Southern Alps.