The climate of India is broadly classified as 'Monsoon type'. This word has been derived from and Arabic word 'mausam' which is characterized by seasonal reversal of wind pattern and associated weather changes over a large area. There are four distinct seasons in India - the cold weather season, the hot weather season, the advancing monsoon season and the retreating monsoon season.
It begins in mid-November in northern India. It gets well established all over the country by December and continues till February. Temperature remains quite low (mean monthly temperature of 15°C-20°C) during this period in most parts of the country. January is the coldest month. But, south India enjoys a moderate climate. The mean monthly temperature in January varies from 8.5°C in to 26.7°C in Thiruvananthapuram. India lies in the trade wind belt of the northern hemisphere. As such northeast trades blow over Indiafrom land to sea and are dry. While blowing over the Bay of Bengal, they pick up moisture and give rain on the Coromandel Coast. These winds are called northeast monsoons. The weather is pleasant with clear sky, low temperature, low humidity and cool breeze. It is, however, disturbed occasionally by shallow cyclonic depressions from the west known as 'western disturbances'. These depressions originate over the Mediterranean Sea. Moving eastward they enter India and cause precipitation over northwest India. It takes place as show fall over the mountains and as rainfall in the plains.
Weather starts changing during February March in a progressive manner from South to North. Temperature starts rising. In March, maximum day temperature generally exceeds 35°C in areas South of the Vindhyas. In April the maximum day temperature exceeds 37°C in the northern plains of India. By mid-May, day temperature may touch 41°C -42°C especially in the north west plains and central India. In the larger parts of the Ganga plains , the hot and dry winds called 'loo' are common. Due to high temperature, air pressure decreases and often gives rise to locally formed dust storms and thunderstorms. At times they bring some rain and cool the atmosphere temporarily.
Intense heating of the land during April-May causes the formation of a low-pressure area over Northwest India. As its intensity increases, the Southeast trade winds get attracted towards it. After crossing the equator, they get deflected towards their right and flow as Southwest monsoon. This is the advancing monsoon season. The Indian peninsula divides them into two main branches-the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch arrives at the West Coast of India and moves northward. The Bay of Bengal branch strikes the Bengal coast and the Southern face of the Shillong plateau. Then it gets deflected and flows westward along the Ganga-Valley.
Both the branches reach India by the beginning of June, which is known as 'Onset of Monsoon'. These winds are full of moisture and hence they cause rainfall. The bulk of the annual rainfall in India is received from the Southwest monsoon. The amount of rainfall is very high along the west coast and in the North East. It gradually decreases away form the sea towards the interior. Tamil Nadu Coast remains mostly dry as it falls in the rain-shadow area of the Arabian Sea branch and is parallel to the Bay of Bengal branch. Rainfall does not take place continuously. After a few days of rainfall, a short spell of dry days is quite common. Thus, the Southwest monsoon season spreads over June to September in most of parts of India
The departure or retreat of the monsoon is gradual. It means weakening of the monsoon current. It with draws form the Punjab plains in mid-September and the Ganga delta by mid-October. It retreats from the Southern part of the peninsula by early November.
Wind direction gradually changes with the weakening of the Southwest monsoon. The Northeast trade winds take over and it is commonly known as the North East monsoon. Tamil Nadu Coast receives most of its rainfall from October to December.
October and November are transitional months between hot rainy season and cold dry weather season. By this time low-pressure area shifts form the Northwestern part of India to the Bay of Bengal. Cyclones originating over the< Bay of Bengal reach the Eastern Coast of India. They cause heavy and widespread rain in the coastal areas of Orissa, Andhra Pradesh and Tamil Nadu. These cyclones are very destructive. The thickly populated deltas of the Godavari, Krishna, Kaveri experience such disasters frequently.
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Advancing Monsoon Season |
Retreating Monsoon Season |
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June, July, August & September are the months of this season |
October and November are the months of this season. |
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Low pressure is formed over |
Low pressure is shifted form Northwest India to the |
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It is the South West monsoon and is divided into the Arabian Sea branch and the |
It is the Northeast monsoon and means weakening of the monsoon current. |
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It has a sudden arrival |
It is departure is gradual. |
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These winds are full of moisture and cause heavy rainfall in most parts of . |
These winds are devoid of moisture and only |
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Rainfall does not take place continuously as there are wet spells and dry spells |
Cyclones originating over the Bay of Bengal reach the |