The India Meteorological Department expects below-normal rainfall over most of India during November, and over the country as a whole, in its monthly outlook issued from New Delhi on 31 October.
The sharpest signal is over South Peninsular India, the five meteorological subdivisions of Tamil Nadu, Puducherry and Karaikkal; Coastal Andhra Pradesh and Yanam; Rayalaseema; Kerala and Mahe; and South Interior Karnataka. That region receives a substantial share of its rain in the October to December season, and November there is most likely to be below normal, which the department defines as less than 77 per cent of the long period average.
The reference figures are modest. Based on data from 1971 to 2020, the November long period average is about 118.7 millimetres over South Peninsular India and about 29.7 millimetres over the country as a whole.
Not everywhere is dry. Normal to above-normal rainfall is considered likely in some areas of central, northwest, east and Northeast India.
On temperature, above-normal maximum temperatures are likely over most of the country, except for regions along the foothills of the Himalayas, where normal to below-normal maxima are expected. Above-normal minimum temperatures are likely over most parts except many parts of central and eastern India.
The forecasts come from a method IMD adopted in 2021, combining its existing statistical system with a multi-model ensemble that draws on coupled global climate models, including the department's own Monsoon Mission Coupled Forecast System. The three tercile categories, above normal, normal and below normal, each carry an equal climatological probability of 33.33 per cent.
On the oceans, the department reports that very strong El Nino conditions are currently prevailing over the equatorial Pacific, and that model forecasts indicate very strong El Nino conditions are likely to persist through November and December. The Indian Ocean Dipole is neutral, and neutral conditions are expected to continue through the post-monsoon season to December.
IMD also provides extended-range forecasts, seven-day averages for the following four weeks, updated every Thursday.
That paragraph on the Indian Ocean deserves setting out exactly as the department set it out, because it contains two statements that are both the department's position and both correct. The dipole "has currently exceeded the positive IOD threshold (+0.4 degrees Celsius)". The dipole is also neutral.
The reconciling sentence sits between them: "sustained values above this threshold are required before an event is considered established". The index has crossed the line. It has not yet stayed across it. Until it does, what is happening in the Indian Ocean is happening without being an event.
This is a stricter test than most phenomena are put to. A positive dipole is not a reading; it is a reading that has demonstrated commitment. The ocean is currently above the threshold on a provisional basis and is being observed to establish whether it meant it.
The rainfall categories run on the same principle from the opposite end. Below normal is less than 77 per cent of the long period average, and the long period average for the whole of India in November is about 29.7 millimetres. The national forecast is therefore for less than roughly 23 millimetres of rain across the month, a departure of some seven millimetres, spread across the country.
Our analysts note that each of the three categories begins the month holding a 33.33 per cent climatological probability before any model is consulted. A forecast of below normal therefore starts one chance in three correct, and is being asked to improve on a coin with three sides.
The Department of Unnecessary Research will be watching the Indian Ocean closely and expects nothing to happen, in the technical sense. The dipole has exceeded the threshold for a positive dipole. It remains neutral, and will remain neutral until it proves it was serious.