WEATHER SYSTEMS WEATHER AND CLIMATE

Weather Weather describes the conditions of the atmosphere at a particular time. Climate describes the long term atmospheric characteristics. It deals with average figures of each element over a period of time, (e.g. average monthly temperatures) etc.

What is Weather Weather describes whatever is happening outdoors in a given place at a given time. Weather is what happens from minute to minute. The weather can change a lot within a very short time. For example, it may rain for an hour and then become sunny and clear. Weather includes daily changes in precipitation, barometric pressure, temperature, and wind conditions in a given location. What is your weather like today?

What is your weather like today? Which picture describes your weather today?

What is Climate Climate describes the total of all weather occurring over a period of years in a given place. This includes average weather conditions, regular weather sequences (like winter, spring, summer, and fall), and special weather events (like tornadoes and floods). Climate tells us what it's usually like in the place where you live.

DIFFERENCES BETWEEN THE TWO Weather is the actual conditions in the atmosphere at a particular place and time over a twenty four hour period. Climate is the average atmospheric conditions a place gets based on a period of over thirty years. The climate of a place is described as its average weather conditions.

Caribbean weather systems A weather system is a large area of the atmosphere that has special temperature and moisture conditions. INTER TROPICAL CONVERGENCE ZONE TROPICAL WAVES HURRICANES COLD FRONTS ANTICYCLONES

I.T.C.Z The ITCZ is an area of low pressure lying east to west across the equatorial region. The hot air from the north east trade winds meet the hot air from the south east trade winds in this region. The hot moist air is forced to rise, resulting in rainfall. This belt of low pressure moves north and south of the equator with the seasons.

I.T.C.Z

I.T.C.Z In June it drifts northwards and may affect Trinidad and Tobago and the rest of the southern Caribbean. In December it drifts south and affects Guyana. It is also active in March and September when the hottest place is the equator.

Conditions associated with the I.T.C.Z Heavy rainfall Overcast skies with cumulus clouds Light and calm winds High temperatures

ITCZ

Tropical Waves They are weak, low pressure systems that lack a closed centre. They form near Africa over the warm waters of the Atlantic Ocean and move westwards into the Caribbean. They affect most of the islands of the Caribbean during the months of June to December.

Tropical Waves

Conditions associated with Tropical Waves Moderate winds Heavy and continuous rainfall Overcast skies High temperatures. Tropical waves can eventually develop into hurricanes. They are not hurricanes since they don’t have a low pressure centre and strong winds.

Tropical Waves

Hurricanes

Hurricanes Hurricanes are strong , low- pressure systems with strong winds of > 120 km per hour. Winds blow into them in an anti-clockwise direction with heavy rainfall. They start off as tropical waves near Africa and move into the Caribbean during June to December.

Hurricanes Warm ocean water >26 degrees celsius. Coriolis effect north and south of latitudes 10 degrees north and south, this causes the spiral motion of the hurricane and influences its path. Divergent upper level winds allowing updraughts of air. Most Caribbean islands are affected by hurricanes.

Hurricanes

Hurricanes Wind speeds above 120 km/ hour. Wind direction varying between north east and south east. Torrential rain Overcast skies with towering cumulonimbus clouds. Thunderstorms with lightning. Temperatures remain high averaging 27 degrees celsius.

Hurricanes

Cold Fronts A front is an area where two air masses of different temperatures meet. Cold dry air moves south from the North American continent and pushes under the warm, moist Caribbean air. The rising warm air cools and condenses resulting in heavy rainfall.

Weather Associated with Cold Fronts Cooler temperatures, 18 – 21 degrees celcius. Moderate rainfall that lasts for days depending on the movement of the frontal system. Moderate cloud cover Winds from the north.

Anticyclones Anticyclones are high pressure systems. Winds blow out of them in an anti- clockwise direction. They form around mid- latitudes and may drift into the Caribbean. They are stable with sinking air blowing out of the centre. They affect most of the Caribbean north of Trinidad and Tobago.

Anticyclones

Weather associated with anticyclones Dry and sunny Clear skies Moderate winds Moderate temperatures