In keeping with its earlier predictions, the India Meteorology Department has unofficially announced that the monsoon has already hit the Andaman Sea, and will hit southern Bay of Bengal a week ahead of the normally expected date. Temperatures in Delhi will fall for the next three days, according to the IMD.

The notoriously inaccurate IMD had said earlier that its prediction of the actual date of the onset of the monsoon in Kerala, the southern bellwether state, could be up to four days before or after its projection. In the forecast on Tuesday, the met department said rain or thundershowers would occur at many places over Andaman and Nicobar Islands, Kerala, Lakshwadeep, Tamil Nadu and Coastal and South Interior Karnataka. 

Some areas in Andhra Pradesh and interior Karnataka too would get showers over the next 24 hours. In the next 48 hours, most places in South India should expect rains, the met said.

For north India, a gentle 'western disturbance' is predicted to cause isolated rain and thundershowers in the states of Jammu and Kashmir, Uttarakhand and Himachal Pradesh over the next two to three days. However, western and central India would largely remain dry and hot though a few places in MP, Marathawada, Konkan and Goa may get some showers.

IMD in its long range forecast for the 2009 south-west monsoon season (June to September) has already said that the average rainfall for the entire country will be what is technically referred to as `near normal' at 96 per cent of the long period average, which is calculated to be 89 cm.

Last week, the weather bureau had forecast the June-September monsoon rains would hit the southern Indian coast on 26 May, ahead of the normal arrival date of 1 June.

However, for farmers across the country region specific updates and the much more focused predictions that IMD brings out later in June are of greater importance. (See: IMD re-affirms prediction of early, strong monsoon)

Numerical weather prediction models indicate gradual increase in the monsoon-driving pressure gradient (from peninsular 'high' to upcountry 'low') over the Bay of Bengal and the Arabian Sea. This would trigger stronger cross equatorial flows and increase in rainfall activity over south peninsula during the next four days. 

Meanwhile, a low-pressure area will form over central Bay of Bengal around Saturday (May 23) and intensify thereafter. International models saw a tropical cyclone spinning up out of the system later on.