The IMD's forecast is subjected to a model error of +/-4%, which means that the rainfall can be in the range of 96% of the LPA to 104% of the LPA.
Along with the even spread of South-West monsoon rains predicted by IMD, the global forecast agencies have dispelled the fears of major flood situations, with exceptions at few places, by predicted the weakening of La Nina conditions (cooling of Pacific waters below normal) the factor responsible for floods across the globe.
Though the rainfall forecast is 100% of the LPA, the IMD has termed it as near normal rainfall. This is because there is no categorization for normal rainfall in the IMD's parameters. Rainfall in the range of 96% to 104% of the LPA is termed near normal, that in the range of 90% to 96% of the LPA is termed below norm and that below 90% of the LPA is termed deficient.
In its initial forecast made in April 16, this year the IMD had said that that the countrywide rainfall in the four-month monsoon season would be 99% of the long period average (LPA) rainfall for the period which is 89 cm subject to a model error of +/-5%.
In its revised forecast released on Monday, the IMD has said that the countrywide rainfall in July the month crucial for agriculture would be 98% of the LPA of 29.3 cm, subject to a model error of +/-9%.
It also said that the average cumulative rainfall over north-west India would be 96% of the LPA of 61.2 cm, subject to a model error of +/-8%. North-west India comprises of Jammu & Kashmir, Himachal Pradesh, Punjab , Rajasthan, Haryana, Chandigarh , Delhi , Uttaranchal and Uttar Pradesh. The rainfall over north-east India would be 101% of the LPA of 142.9 cm, subject to a model error of +/-8%. North-east India consists of Arunachal Pradesh, Meghalaya , Assam , Nagaland, Manipur, Mizoram, Tripura , Sikkim , West Bengal , Bihar and Jharkhand.
For central India consisting of Gujarat, Madhya Pradesh, Chhattisgarh, Maharashtra , Goa and Orissa, the IMD has predicted rainfall amounting to 101% of the LPA of 99.4 cm, subject to a model error of +/-8%.
Rainfall over southern peninsula consisting of Andhra Pradesh, Karnataka, Tamil Nadu, Kerala and the island territories Andaman & Nicobar Islands and Lakshadweep would be 98% of the LPA of 72.5 cm.
The US-based International Research Institute for Climate and Society has, however identified some areas of excess rainfall in the country. In its recent forecast it said: "In parts of northern India near Nepal in July-September, 2008, there is a 40% probability of that the precipitation will be in the wettest third of the years, a 35% chance it will be in the near-normal third of the years and a 25% chance that the precipitation will be in the driest third of the years."
According to IRI in August there would be heavy rainfall over central India , in September and October there would be heavy rains over eastern Gujarat and Rajasthan.
This year the South-West Monsoon set in over south Andaman Sea on May 10, about 5 days earlier than the normal date. It set in over Kerala coast on May 31, close to its normal date, June 1. It advanced rapidly and covered parts of south peninsula and entire northeastern region by June 2. It reached Mumbai on June 7, three days earlier than the normal date and reached southern parts of Gujarat on June 10, five days earlier. Monsoon arrived in Delhi on June 15, two weeks ahead of the schedule. But monsoon is yet to cover parts of west Rajasthan, the due date of which is July 1.Till June 25, the average cumulative rainfall over the country was 26% more than the normal, with 17 out of 36 meteorological sub-division receiving excess rains and 10 receiving normal rains. Floods were reported in some areas of excess rainfall.