India monsoon progress and outlook
By
Jason Nicholls, AccuWeather senior meteorologist
Published Jul 16, 2020 5:49 PM EDT
India is currently about a month and a half into their southwest monsoon season that typically runs from June through September, so let's look at how rainfall has stacked up so far. First, looking at India as a whole, we can see that the monsoon started off strong in early June but trailed off some later in June and early July. According to the IMD, cumulative rainfall over India as a whole through 16 July is 9.7% above normal.
As is normally the case, rainfall has not been evenly distributed across India. Looking at a regional breakdown of the rainfall so far, we can see that northwestern India is the only area running a deficit on rainfall, but it is a large deficit of nearly 16% below normal. There are some other drier areas scattered across India, namely portions of Karnataka, Goa, Kerala and Odisha into West Bengal among others.
A big factor in the monsoon rainfall through mid-July has to be the Madden-Julian Oscillation (MJO) which has been stalled in phases 1 and 2 through most of the period. Based on research papers, an MJO pulse in phases 7, 8, 1 and 2 tends to suppress rainfall across northern India, especially in the northwest. Looking at the right-hand side of the image below, we can see phases 3, 4, 5 and 6 are best for rainfall in a large part of India.
The stalled MJO is also a large factor as to why there have been very few monsoon lows over the Bay of Bengal so far this monsoon season. A paper by Philip J. Klotzbach relating the MJO to tropical cyclone development in the various basins shows a significant lack of cyclone development in the northern Indian Ocean with the MJO in phases 1, 2 and 3. Some of the same factors that lead to tropical cyclone development also figure into monsoon low development, especially the suppressive and active parts of MJO pulses. Therefore, it is clear that the MJO has been stalled in an unfavorable location for monsoon low formation in the Bay of Bengal but has spawned a pair of lows over the Arabian Sea.
The forecasts for the MJO (below) show no signs of the MJO moving into the more favorable phases anytime soon, but the good news is that the MJO should weaken. A weak MJO signal tends to lead to improved rainfall prospects over portions of northern and western India.
Other factors we are watching for the remainder of the monsoon season are ENSO and the IOD which are both currently neutral. However, there are already signs of cooling across the eastern and central equatorial Pacific which can indicate a developing La Nina as many long-range models are showing. We expect weak La Nina conditions to develop later in August or September which may give a boost to late-season rainfall. There are some model differences regarding the IOD going forward, but the consensus continues to favor a neutral to weakly negative IOD heading into boreal autumn.
Courtesy of the Australia BOM
Overall, the IOD will likely not be as significant of a factor with the monsoon like it was in 2019 when the record strong positive IOD boosted monsoon rains late in the season following a slow start. However, it appears the IOD will likely be too weak to be a major factor during the second half of the 2020 season. The positive impacts from La Nina may also be limited, so the MJO and other factors may remain the main drivers for the remainder of the season.
So what does all this mean for the rest of the 2020 monsoon season? Looking at some model output, there is fair agreement that the weakening of the MJO should lead to better rains across a good portion of northern into central India for late July into early August.
Developing La Nina conditions could also lead to near- to above-normal rainfall across dry northwestern India during August into September. If the model outlooks are correct, better rains late in the season can help erase the early season deficits. Meanwhile, rainfall prospects look to wane across northeastern and eastern India late in the season.
Southwestern India can also expect near- to above-normal rainfall for the rest of the season, while southeastern India, namely Andhra Pradesh and Tamil Nadu, should be on the dry side of normal.
As always, stay tuned to AccuWeather.com for updates on short-term weather across India as well as any updates to monsoon seasonal outlook.
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Weather Blogs / Global weather
India monsoon progress and outlook
By Jason Nicholls, AccuWeather senior meteorologist
Published Jul 16, 2020 5:49 PM EDT
India is currently about a month and a half into their southwest monsoon season that typically runs from June through September, so let's look at how rainfall has stacked up so far. First, looking at India as a whole, we can see that the monsoon started off strong in early June but trailed off some later in June and early July. According to the IMD, cumulative rainfall over India as a whole through 16 July is 9.7% above normal.
Courtesy of the IMD
As is normally the case, rainfall has not been evenly distributed across India. Looking at a regional breakdown of the rainfall so far, we can see that northwestern India is the only area running a deficit on rainfall, but it is a large deficit of nearly 16% below normal. There are some other drier areas scattered across India, namely portions of Karnataka, Goa, Kerala and Odisha into West Bengal among others.
Courtesy of the IMD
Courtesy of the IMD
A big factor in the monsoon rainfall through mid-July has to be the Madden-Julian Oscillation (MJO) which has been stalled in phases 1 and 2 through most of the period. Based on research papers, an MJO pulse in phases 7, 8, 1 and 2 tends to suppress rainfall across northern India, especially in the northwest. Looking at the right-hand side of the image below, we can see phases 3, 4, 5 and 6 are best for rainfall in a large part of India.
The stalled MJO is also a large factor as to why there have been very few monsoon lows over the Bay of Bengal so far this monsoon season. A paper by Philip J. Klotzbach relating the MJO to tropical cyclone development in the various basins shows a significant lack of cyclone development in the northern Indian Ocean with the MJO in phases 1, 2 and 3. Some of the same factors that lead to tropical cyclone development also figure into monsoon low development, especially the suppressive and active parts of MJO pulses. Therefore, it is clear that the MJO has been stalled in an unfavorable location for monsoon low formation in the Bay of Bengal but has spawned a pair of lows over the Arabian Sea.
The forecasts for the MJO (below) show no signs of the MJO moving into the more favorable phases anytime soon, but the good news is that the MJO should weaken. A weak MJO signal tends to lead to improved rainfall prospects over portions of northern and western India.
Other factors we are watching for the remainder of the monsoon season are ENSO and the IOD which are both currently neutral. However, there are already signs of cooling across the eastern and central equatorial Pacific which can indicate a developing La Nina as many long-range models are showing. We expect weak La Nina conditions to develop later in August or September which may give a boost to late-season rainfall. There are some model differences regarding the IOD going forward, but the consensus continues to favor a neutral to weakly negative IOD heading into boreal autumn.
Courtesy of the Australia BOM
Overall, the IOD will likely not be as significant of a factor with the monsoon like it was in 2019 when the record strong positive IOD boosted monsoon rains late in the season following a slow start. However, it appears the IOD will likely be too weak to be a major factor during the second half of the 2020 season. The positive impacts from La Nina may also be limited, so the MJO and other factors may remain the main drivers for the remainder of the season.
So what does all this mean for the rest of the 2020 monsoon season? Looking at some model output, there is fair agreement that the weakening of the MJO should lead to better rains across a good portion of northern into central India for late July into early August.
Courtesy of the IMD
Developing La Nina conditions could also lead to near- to above-normal rainfall across dry northwestern India during August into September. If the model outlooks are correct, better rains late in the season can help erase the early season deficits. Meanwhile, rainfall prospects look to wane across northeastern and eastern India late in the season.
Southwestern India can also expect near- to above-normal rainfall for the rest of the season, while southeastern India, namely Andhra Pradesh and Tamil Nadu, should be on the dry side of normal.
As always, stay tuned to AccuWeather.com for updates on short-term weather across India as well as any updates to monsoon seasonal outlook.
Report a Typo