Although moderate to heavy rains have been lashing most parts of Kerala for some days, the India Meteorological Department (IMD) made the monsoon announcement only Tuesday.

Kottayam, Alappuzha, Ernakulam and Kasargode have been lashed by rains. The sea turned rough in Alappuzha, with sea waters encroaching into land at a few places.

But the dry weather continued in the southern districts of Kollam and Thiruvananthapuram.

The monsoon accounts for 80 percent of the rainfall in India. Even a minor delay can adversely affect the economy as about half of India's farm output comes from crops sown in the June-September rainy season.

IMD director general L.S. Rathore told IANS in New Delhi that the monsoon was expected to advance rapidly into other parts of the country. Karnataka would be lashed by heavy rains within days.

Kerala gets the annual monsoon rains June 1, marking the start of weeks of showers in the Indian mainland. Last year, however, the monsoon arrived in the state May 29.

Rathore said there was nothing to panic as the four-day monsoon delay was well within the forecast limits.

From 2005, the IMD has been issuing operational forecasts for the onset of the monsoon over Kerala using an indigenously developed statistical model with a model error of (+/-) four.

The IMD has said that the 2012 southwest monsoon season (June-September) for the country as a whole was most likely to be normal.

"The deviation in arrival of monsoon rains would have no adverse impact on sowing of kharif (summer) crops like paddy and pulses," he said.

The monsoon normally reaches Delhi by June-end. but according to IMD it is too early to say when the capital will get rains.

"We can only make date specific forecast towards the end of this month by seeing the spread of monsoon in the rest of the country," IMD director B.P. Yadav told IANS.

Agriculture expert Devinder Sharma was, however, cautious.

"The delay in monsoon by a day or two is fine. But the most important thing is the spread of monsoon during June and July, the sowing season for kharif crops," Sharma told IANS in Delhi.

He said that in last few years, there have been cases when monsoon arrived before time but states like Rajasthan, Gujarat and Bihar did not receive sufficient rains, leading to crop failure.

"I am more worried about the spread of monsoon as more than half of our crop production is dependent on the southwest monsoon," he added.

IMD official K. Santhosh in Thiruvananthapuram said he was getting telephone calls demanding to know why the announcement of monsoon arrival was made when the city was yet to get rains.

Santhosh said a few indicators determine the announcement.

"We have 14 weather stations located at Lakshadweep, in Kerala and in Mangalore. We start to monitor the rains from May 10. If 60 percent of the stations or more record 2.5 mm of rain for two continuous days, then it satisfies the criterion that monsoon has arrived," Santhosh told IANS.

"Another indicator for the declaration is the strength of the wind," he added. Cloud movements are another indicator.