Given the geographical position of southern peninsular India, being at a low latitude close to the equator, it starts witnessing the heat much earlier than the rest of the country. Spring brings a certain resemblance to a summer season for this topography.

One of the significant observations is the prominent land heating over the Deccan Plateau, mainly in Andhra Pradesh’s Rayalaseema and adjacent northern Karnataka. This heat causes the formation of heat low over the land, which is more dominant around Rayalaseema. It also causes the development of a thermal north-south trough running from south Tamil Nadu into Madhya Pradesh and Chhattisgarh through the interior parts of the peninsula, which becomes significant as land heating progresses.

The other salient feature is the appearance of two anticyclones in the lower troposphere on either side of peninsular India during the March-April months. The Arabian Sea anticyclone pushes hot, continental dry air into India through the west-northwest; while on the contrary, the Bay of Bengal’s anticyclone introduces a relatively cool, moist air mass from the Bay of Bengal.

An anticyclone is an area of high pressure where air moves apart and sinks or moves downward.

The interaction between these two types of air masses forms the line of moisture discontinuity. Clouds or thunderstorms form over this point of interaction whenever the atmospheric conditions turn favourable.

The Arabian Sea anticyclone, the stronger and larger of the two, remains for almost three months, disappearing only after the onset of the monsoon, in late May or early June. The Bay of Bengal anticyclone introduces cool winds from the Bay, maintaining the temperature along the east coast. However, this anticyclone disappears much earlier, by late April or early May, setting the stage for the onset of the monsoon.

These, coupled with intraseasonal equatorial wave modulation, outline the seasonal dynamics of the peninsular region.