Weather and Climate NZ

Climate

The average weather conditions of a place over several decades (30+ years). Long-term stable pattern, not day-to-day changes.

Weather

Atmospheric conditions over a short time (a day or week). Temperature, rainfall, wind on a specific day. Changes daily.

Latitude

Distance from the equator. Lower latitude = closer to equator = more direct sun = warmer. Auckland (37°S) warmer than Dunedin (46°S).

Altitude

Height above sea level. Higher = colder. Air thins at height and absorbs less heat. Drops ~1°C per 100m.

Relief

Mountains force moist air upward → cools → orographic rain on windward side → dry rain shadow on leeward side.

Orographic (Relief) Rainfall

Moist air forced over mountains → rises → cools → rain on windward side. Dry air descends leeward side = rain shadow. Example: Hokitika, West Coast.

Frontal (Cyclonic) Rainfall

Warm moist air meets cold air at a front → warm air rises over cold → cools → rain. Associated with depressions (L). Most common in NZ.

Convectional Rainfall

Sun heats ground → heats air above → air rises → cools at altitude → thunderstorms. Happens on hot still days. Common in Northland in summer.

Rain Shadow

Dry area on the leeward (sheltered) side of mountains. Air drops rain on windward side, leaving little moisture for the other side. Example: Alexandra.

Maritime Climate

Influenced by proximity to ocean. Mild winters, cool summers, small seasonal range. Regular rainfall. Example: Auckland, Wellington.

Continental Climate

Inland, far from ocean. Extreme temperatures

Anticyclone (H)

High pressure. Air descending. Fine, clear, settled weather. Wide isobars = light winds. Winds flow anticlockwise in Southern Hemisphere. Pressure 1010–1030mb.

Depression (L)

Low pressure. Air rising. Wet, windy, cloudy weather. Close isobars = strong winds. Winds flow clockwise in Southern Hemisphere. Pressure 990–1010mb.

Isobars

Lines on a weather map connecting places of equal air pressure. Drawn at 5mb intervals. Close together = strong winds. Far apart = light winds.

Barometer

Measures air pressure in millibars. Rising pressure = fine weather coming. Falling pressure = rain/storms coming.

Anemometer

Measures wind speed. Spinning cups catch the wind

Rain Gauge

Measures amount of precipitation (rainfall) in mm over a set time period.

Thermometer

Measures air temperature in °C. Glass tube with mercury or alcohol that expands when heated.

Greenhouse Effect

Sun heats Earth → Earth releases infrared heat → CO₂ traps it like a blanket. Naturally keeps Earth warm. Humans adding CO₂ by burning fossil fuels = enhanced warming.

Global Warming

Rising global temperatures from humans increasing CO₂ → stronger storms, rising sea levels, melting ice.

El Niño

Pacific winds weaken → warm water shifts east toward South America → disrupts global rainfall. NZ gets cooler/drier in north & east. Natural cycle every 2–7 years. NOT human-caused.

Cyclone Gabrielle

February 2023 tropical cyclone. Hit Hawke's Bay, Gisborne, Northland. National state of emergency. ~11 deaths, $14bn+ damage. More intense due to warmer seas from climate change.

Tropical Zone

0–23°N/S. Near equator. Hot year-round (25–30°C). High rainfall. Sun hits at direct angle = intense solar radiation.

Temperate Zone

23–66°N/S. Mid-latitudes. Moderate temperatures. Four seasons. New Zealand sits here (Southern Temperate Zone).

Polar Zone

66–90°N/S. Near poles. Very cold year-round. Sun hits at very low angle. Permanent ice and snow.

Why is Wellington windy?

Cook Strait funnels prevailing westerly winds through a narrow gap, accelerating them. Wellington is directly exposed with no shelter.

Why is Hokitika wet?

Westerlies absorb moisture over Tasman Sea → hit Southern Alps → forced up → orographic rain on windward West Coast. ~2800mm/year.

Why is Alexandra dry?

Sits in rain shadow of Southern Alps on the leeward eastern side. Westerlies drop rain on the West Coast first. Only ~330mm/year.