Forecasting rainfall trend over India during summer monsoon

Cold fronts with associated westerly waves (mid-latitude low pressure systems: 30 degrees S-60 degrees S) move north of 30 degrees S from west coast of South Africa (10 degrees E or even from 40 degrees W) to west coast of Australia (120 degrees E) during southwest monsoon season (winter season: southern hemisphere). They influence Indian summer monsoon rainfall significantly. Geo-potential height field of 850 hPa levels undergoes large changes in association with the movement of cold fronts/upper air troughs from 040 degrees W to 120 degrees E / 140 degrees E and north of 30 degrees S/40 degrees S during April-May. Moisture generated over Atlantic and Indian Oceans (from east of 40 degrees W to 120 degrees E) by cold fronts/upper air troughs augment south easterly trades through low level subtropical anticyclones during summer monsoon season as they move eastwards and equator-wards. Positive (high) and negative (low) anomalies of 850 hPa level geo-potential heights during April-May, north of 40 degrees S from 40 degrees W to 120 degrees E/140 degrees E have been used to forecast rainfall trend over India during the first week of June.