Fog in Wellington Harbour
Fog in Wellington Harbour

Southerlies bring fogs through Cook Strait and up the Coast

By Alan Tristram 

NIWA has told the Independent this week’s Kapiti fogs are typical of advection fogs, when moist air intrudes over a cold surface.

This is the result of weak southerly flows bringing low stratus cloud and fog along the east coast of the South Island, and into Cook Strait and up the Kapiti Coast.

 The National Institute of Water and Atmospheric Research (full title) adds:

“Fog is not unusual at this time of year. It typically forms when moist air comes into contact with a cool surface. The air cools and condenses into visible water droplets.

“Fogs form after radiative cooling, when the ground loses heat rapidly at night in still conditions, and through advection,

It also says that while radiation fogs generally lift after daylight as the sun heats the moist air, advection fogs typically clear after a change in wind direction, with the arrival of a drier air mass.