South Asia 2023 Monsoon Outlook

The southwest monsoon impacts South Asia from June through September and is an important period for agriculture. Before we jump to the forecast, we will quickly look at some teleconnections.

Some winter sea-surface temperature teleconnections include water temperatures off northwestern Australia and the northern Arabian Sea. The cool waters off northwestern Australia and in the northern Arabian Sea this past winter may signal a weak summer monsoon across South Asia.

Looking at sea-surface temperature anomalies over the central Indian Ocean this past autumn, we see anomalies near to below historical averages which may also signal a weak monsoon. However, this teleconnection is not as pronounced as others.

Some other SST-based teleconnections include the Atlantic Multi-decadal Oscillation (AMO), Pacific Decadal Oscillation (PDO) and the Indian Ocean Dipole (IOD). As the climate models show, we are expecting a warm AMO and a negative PDO possibly trending to neutral. The warm AMO is a favorable signal for rainfall in South Asia this summer. The currently negative PDO is a favorable sign for rainfall during the summer monsoon, but if the PDO trends to neutral as many climate models suggest, then the PDO may become less of a factor during the season.

The IOD is neutral to weakly positive but is expected to become weak to moderately positive later in the summer going into autumn which may help boost rainfall late in the monsoon. However, the expected positive IOD may be counteracted by ENSO which we will look at next.

The triple La Nina finally came to an end during March, and the ENSO is expected to remain neutral over the next month or two, but El Nino conditions are expected to develop in June or July. The reversal of the South Pacific Oscillation (SPO) and South Pacific Meridional Mode (SPMM) to positive as well as the Pacific Meridional Mode (PMM) becoming warm all favor El Nino conditions developing as many climate models suggest.

According to a paper by Arindam Chakraborty, La Nina followed by a neutral ENSO reduces rainfall across India by 4%. As the following figure shows, drying across India is more pronounced when La Nina is followed by El Nino conditions. As a result, the transitioning ENSO may end up being a big factor for the summer monsoon.

Multiple teleconnections are pointing toward a down year for the monsoon across South Asia in 2023 as well as fewer monsoon lows and a lesser chance for pre-monsoon tropical activity in the northern Indian Ocean. Overall, we are expecting one or two depressions or stronger systems in the Bay of Bengal from April into June with the chance for zero or one depression or stronger in the Arabian Sea during the period. For the season, we are predicting two to four monsoon lows which can be down from last year.

Now that we touched on some teleconnections, here is what many climate models suggest for rainfall during the summer monsoon. Most modeling suggests rainfall near to below historical averages across much of South Asia this monsoon season.

Our analog years, shown below, suggest a drier idea than the modeling with a mean all India rainfall for the analog years being 89% of historical averages with a median of 91%.

Now that we have looked at rainfall across South Asia during the monsoon, we are looking at the Southern Oscillation Index (SOI) as a sign of when the monsoon may arrive in Kerala. A strongly positive SOI prior to the monsoon season and an easterly QBO normally favor a monsoon onset in Kerala around the normal onset date of 1 June. However, this year, we have an SOI trended more strongly negative and a westerly QBO, so we are leaning toward a delayed onset of around 3 June, plus or minus five days.  

Now that we looked at several teleconnections, below is our outlook for the South Asia monsoon season.

All India rainfall is expected to be much lower than in 2022 when we had all India rainfall around 105% of historical averages. This year we are going with all India rainfall of around 92% of historical averages, plus or minus 5%.

The expected monsoon lows in the Bay of Bengal, although down, may favor rainfall near to perhaps above historical averages in Bangladesh and northeastern India across southern West Bengal, Jharkhand, Odisha and perhaps parts of Chhattisgarh. The influence of these lows could reach as far west as Madhya Pradesh enough to get the area closer to historical averages. Meanwhile, areas farther west, such as Maharashtra, Rajasthan and Gujarat into central and southern Pakistan, will be drier than last year as well as historical averages. We are also leaning toward rainfall near to perhaps a little above the historical average in Sri Lanka and Tamil Nadu into Kerala.

There is a chance that pre-monsoonal rains can result in rainfall near long-term averages in northern Pakistan, Jammu and Kashmir, Punjab, Haryana, Rajasthan, Gujarat and perhaps parts of Madhya Pradesh during the month of June. The development of a +IOD may favor better rainfall in these same areas late in the season as well as a delayed withdrawal.

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