Plain words

Weather glossary

The words you hear on the forecast, explained in plain language. Tap a letter to jump to it, or use your browser's find to search for a word.

A

Air quality index (AQI): A 0 to 500 scale for how clean the air is. The higher the number, the more polluted the air. This site uses the US scale.

Dew point: The temperature the air has to cool to before its water vapour turns into droplets. When the dew point is in the mid-20s °C or higher, the air feels sticky and muggy.
Dry season: In Trinidad and Tobago, January to May. There is less rain, though short showers can still come.

Earthquake magnitude: The size of an earthquake. The scale is logarithmic: each whole number up releases about 32 times more energy. Quakes under about 3 are often not felt.

Feels like: The temperature the body actually feels. It combines the air temperature with humidity, wind and sun. See heat index.
Flash flood: Sudden flooding that starts within a few hours of heavy rain, often in low spots, gullies and roads that drain poorly. Move to higher ground and never drive through floodwater.

Gust: A short, sudden burst of wind that is stronger than the average wind speed around it.

Heat index: How hot it feels once humidity is counted in. Sweat dries slowly in damp air, so the body cools less well and the same temperature feels hotter.
Humidity: The amount of water vapour in the air, shown as a percentage of the most it could hold at that temperature. High humidity means damp, sticky air that is harder to cool down in.
Hurricane: A tropical storm with sustained winds of 119 km/h (74 mph) or more. In the Atlantic, the hurricane season runs from 1 June to 30 November.
Hurricane categories: A scale from 1 to 5, set by the one-minute sustained wind speed. Category 3 and above is called major.
Category Wind (km/h)
1 119 – 153
2 154 – 177
3 · major 178 – 208
4 209 – 251
5 252 +
Hurricane watch and warning: A watch means hurricane conditions are possible within 48 hours. A warning means they are expected within 36 hours. Follow TTMS and ODPM for official alerts.

Isolated, scattered, widespread: Words for how much of an area gets the weather. Isolated: a few spots. Scattered: some spots. Widespread: most of the area.
ITCZ: The Intertropical Convergence Zone: a band near the equator where the trade winds from the north and south meet. When it drifts up near Trinidad, expect heavy, long-lasting rain.

Lightning and thunder: Lightning is the bright flash and thunder is the sound it makes. If you can hear thunder, you are close enough to be struck. Go indoors and wait 30 minutes after the last rumble.
Lime: Caribbean slang for hanging out with friends, usually outside. The Lime guide rates the best times of the day for it.
Low pressure: Air that is rising and cooling, which often brings cloud and rain. Storms and tropical waves form in low-pressure areas.

Petit Carême: A hot, drier spell in the middle of the wet season, often in September and October. It is a break in the rain, not the end of it.
PM2.5: Tiny particles of dust, smoke and pollution, 2.5 micrometres or less across. They reach deep into the lungs, so they matter most for asthma and heart problems.

Rain chance: The chance that rain will fall at a given spot during the time shown. It is not how much rain will fall. A high number means rain is more likely, not that it will rain all day.
Rip current: A narrow channel where water flows fast away from the shore. If you are caught in one, swim parallel to the beach until you are out of it, then swim in. Never fight it straight on.

Saharan dust: Desert dust blown across the Atlantic by the trade winds, mostly from June to August. It makes the sky hazy, lowers air quality and is harder on asthma. Dust also tends to hold back storm formation.
Storm surge: A rise of sea water pushed onto land by a storm's winds and low pressure. For coasts, it is often the most dangerous part of a hurricane.
Sustained wind: The average wind speed over about one minute. Storms are rated by this, not by their gusts.
Swell: Long, regular waves made by storms far away. They can arrive on a calm day and hit harder than the wave height suggests. Swim where lifeguards are posted.

Thunderstorm: A storm with lightning and thunder, formed when warm, moist air rises fast. Often brief but heavy.
Trade winds: Steady winds that blow from the east across the tropics. They bring our usual breeze and steer tropical waves westward.
Tropical depression: An organised system of storms with winds below 63 km/h (39 mph).
Tropical storm: An organised storm with winds of 63 to 117 km/h (39 to 73 mph). Once it reaches this strength, it gets a name.
Tropical wave: A ripple of low pressure that rides the trade winds from Africa, east to west. It brings a day or two of showers and thunder. A few grow into storms.

UV index: How strong the sun's burning rays are, on a scale from 0 up to 11 and more. 8 and above is very high: cover up, wear a hat and sunscreen, and limit time in the midday sun.

Wave height: The distance from the bottom of a wave to its top. The sea bath check rates the sea by this: calm under 1.2 m, choppy to 2 m, rough above.
Wet season: In Trinidad and Tobago, June to December. Expect more rain than in the dry season.
Wind direction: The direction the wind blows from. A north-east wind blows from the north-east, towards the south-west.