Monsoon may start to withdraw around normal Sept timeline 

Forest outlook from the South Korean model suggests that the monsoon may start withdrawing from South-West Rajasthan and adjoining North-West Gujarat around September 1, if not earlier. All indications are that the ongoing lean phase over the region and adjoining North-West India would seamlessly coalesce int the withdrawal schedule. 

Two model flavours

The South Korean models has generated outlook in two flavours — deterministic MME forecast and probabilistic MME forecast. Deterministic plans provide exact average quantities with an understood but unquantified uncertainty while probabilistic methods present the uncertainty accurately. The probabilistic format has been argued to be comparably more informative and valuable. 

Month-wise outlook from September, the last month of the South-West monsoon, through October, November and December (North-East monsoon for the South Peninsula, also called the monsoon in reverse) and the first two months of the New Year (January and February, 2024) is as follows:

Probabilistic MME forecasts

September: Below-normal for southern and eastern parts of Gujarat, and climatological dry for South-West Rajasthan from where monsoon starts to withdraw; below-normal also for West and Central Madhya Pradesh; West Maharashtra; Goa and Coastal Karnataka. Normal elsewhere.

Normal for North, North-West, East, East-Central India; western parts of peninsular India in Odisha, Andhra Pradesh and Telangana; Tamil Nadu and most of Kerala. Wave of rainfall (above-normal) from South Arabian Sea and the Laccadive Sea seen affecting extreme southern parts of Tamil Nadu. 

October: Southerly rain regime persists and extends coverage into more parts of southern Kerala and adjoining Tamil Nadu. 

Deterministic MME forecast: 

September: Above-normal rain for extreme South Kerala and South-East Tamil Nadu; parts of North Coastal Andhra Pradesh and Coastal Odisha, southern parts of Jharkhand; and plains of West Bengal. 

October: Above normal rainfall regime expands further into Central Kerala and parts of adjoining Kerala as well as ghats in the southern parts of neighbouring Tamil Nadu. Above-normal rain for most of North-West and West India, including most of Gujarat, entire Rajasthan, Punjab, Jammu & Kashmir, Ladakh, Himachal Pradesh, parts of Haryana, Chandigarh, Delhi, South Uttar Pradesh and Central Uttar Pradesh. Below-normal for Uttarakhand, most of Uttar Pradesh, Bihar, Jharkhand, Chhattisgarh, Odisha, Vidarbha, Maharashtra, Andhra Pradesh, Telangana, Rayalaseema and northern half of of Tamil Nadu.

Good November seen

November: above-normal rain the country except coast of Odisha and Andhra Pradesh, parts of Rayalaseema and entire Telangana. Both models tend to agree on the same outlook for the month. 

December: Deterministic MME model shows below-normal rain for entire South Peninsula across Tamil Nadu, Kerala, Karnataka, Rayalaseema, and Telangana. The shortfall is pronounced over Coastal and Interior Tamil Nadu and South Kerala. Below-normal rain may extend to adjoining parts of Goa, Madhya Maharashtra and southern parts of Coastal Andhra Pradesh. The rest of the country may receive above-normal to excess rain. The excess rain may pan out over Jammu & Kashmir, Ladakh, Himachal Pradesh, Punjab, Haryana-Chandigarh-Delhi and adjoining West Uttar Pradesh. The probabilistic MME model mirrors the same outlook for the most part. 

Peep into New Year

January, 2024: Both models converge over the possibility of a persisting below-normal rainfall regime for the South Peninsula while the rest of the country may experience normal to above normal rain, with above-normal belt extending from North-West India into East Uttar Pradesh, East Madhya Pradesh, Vidarbha and Chattisgarh. In February, too, there is model consensus on the outlook for the country at large — dry over South and wet over North.