Northeast Monsoon recap and look ahead
By
Jason Nicholls, AccuWeather senior meteorologist
Updated Jan 1, 2021 6:13 PM EDT
The northeast monsoon in southern India and Sri Lanka is typically defined as occurring from October through December, but sometimes the withdrawal of the monsoon is delayed, especially during La Nina years and when a strong positive Southern Oscillation Index (SOI) occurs late in the season. We had both moderate La Nina conditions and a strong +SOI during November and December, which may mean the northeast monsoon is not quite finished. However, before looking ahead to what January holds, we will recap the northeast monsoon from October through December.
Looking at the beginning of the season, we can see that much of southern India had near- to above-normal rainfall during October and November, but Sri Lanka averaged drier than normal. The dryness in Sri Lanka during this time was mostly driven by a delay in the onset of the monsoon and an overall dry October. Rains increased across Sri Lanka in November.
The overall wet pattern continued across southern India and Sri Lanka during the month of December, though there were a periodic breaks in the monsoon. Below is a look at December rainfall, as well as the percent of normal rainfall for the region from October through December.
December rainfall anomalies courtesy of the IMD
The northern Indian Ocean tropical season has a second peak during the period of the northeast monsoon and although there were a few depressions in the basin during October, the first named cyclone in the Bay of Bengal during this period did not form until late November. Very Severe Cyclonic Storm Nivar struck southern India around Puducherry on 25 Nov. Cyclonic Storm Burevi formed on the heels of Nivar and struck eastern Sri Lanka on 2 Dec., before entering and stalling over the Gulf of Mannar from 3 through 5 Dec. These tropical systems certainly helped lead to the widespread above-normal rainfall for southern India and Sri Lanka.
Now that we have looked back at the typical northeast monsoon, we will see what to expect across southern India and Sri Lanka during January. As mentioned earlier, there is currently moderate La Nina conditions and will continue through January and likely into boreal spring. La Nina conditions and the Southern Oscillation Index are good teleconnections for the monsoon in India, especially the SOI which is the atmospheric indicator for ENSO. The SOI is typically +7 or above during a La Nina. The teleconnection with SOI is that a +SOI in September means a slow start and delayed onset for the northeast monsoon, but the teleconnection actually flips as the northeast monsoon season progresses where a +SOI during November and December usually means a slower-than-normal withdrawal.
Courtesy of the Government of Queensland
We can see that the SOI has been strongly positive during November and December, with the SOI in the December the most strong positive since December 2011, which was also a La Nina year. Looking at some other more near-term factors the Madden-Julian Oscillation (MJO) looks to return to the Indian Ocean in early January, which is good for allowing rain to fall in southern India and Sri Lanka.
There is also signs of some equatorial Rossby Wave activity over the region during the first half of January, which should also help with rainfall in southern India and Sri Lanka. All these signs lead us to believe that much of Tamil Nadu, Kerala and perhaps southern Karnataka in India as well as Sri Lanka should be wetter than normal through at least the middle of January.
Model data on the right is courtesy of the JMA
Looking ahead to later in January, rains may ease during the second half of January, but the third and fourth weeks of the month are still expected to average at least close to normal as far as rainfall. There is a good chance the third week of January can still be on the wetter side of normal as the ECMWF and CFS weeklies suggest.
Many global climate models, as shown above, support our idea of wetter-than-normal January across much of southern India and Sri Lanka. Rainfall may return to more typical levels across these areas in February, but Sri Lanka could remain in the wetter-than-normal pattern into February.
Report a Typo
Weather Blogs / Global weather
Northeast Monsoon recap and look ahead
By Jason Nicholls, AccuWeather senior meteorologist
Updated Jan 1, 2021 6:13 PM EDT
The northeast monsoon in southern India and Sri Lanka is typically defined as occurring from October through December, but sometimes the withdrawal of the monsoon is delayed, especially during La Nina years and when a strong positive Southern Oscillation Index (SOI) occurs late in the season. We had both moderate La Nina conditions and a strong +SOI during November and December, which may mean the northeast monsoon is not quite finished. However, before looking ahead to what January holds, we will recap the northeast monsoon from October through December.
Looking at the beginning of the season, we can see that much of southern India had near- to above-normal rainfall during October and November, but Sri Lanka averaged drier than normal. The dryness in Sri Lanka during this time was mostly driven by a delay in the onset of the monsoon and an overall dry October. Rains increased across Sri Lanka in November.
The overall wet pattern continued across southern India and Sri Lanka during the month of December, though there were a periodic breaks in the monsoon. Below is a look at December rainfall, as well as the percent of normal rainfall for the region from October through December.
December rainfall anomalies courtesy of the IMD
The northern Indian Ocean tropical season has a second peak during the period of the northeast monsoon and although there were a few depressions in the basin during October, the first named cyclone in the Bay of Bengal during this period did not form until late November. Very Severe Cyclonic Storm Nivar struck southern India around Puducherry on 25 Nov. Cyclonic Storm Burevi formed on the heels of Nivar and struck eastern Sri Lanka on 2 Dec., before entering and stalling over the Gulf of Mannar from 3 through 5 Dec. These tropical systems certainly helped lead to the widespread above-normal rainfall for southern India and Sri Lanka.
Courtesy of Wikipedia
Now that we have looked back at the typical northeast monsoon, we will see what to expect across southern India and Sri Lanka during January. As mentioned earlier, there is currently moderate La Nina conditions and will continue through January and likely into boreal spring. La Nina conditions and the Southern Oscillation Index are good teleconnections for the monsoon in India, especially the SOI which is the atmospheric indicator for ENSO. The SOI is typically +7 or above during a La Nina. The teleconnection with SOI is that a +SOI in September means a slow start and delayed onset for the northeast monsoon, but the teleconnection actually flips as the northeast monsoon season progresses where a +SOI during November and December usually means a slower-than-normal withdrawal.
Courtesy of the Government of Queensland
We can see that the SOI has been strongly positive during November and December, with the SOI in the December the most strong positive since December 2011, which was also a La Nina year. Looking at some other more near-term factors the Madden-Julian Oscillation (MJO) looks to return to the Indian Ocean in early January, which is good for allowing rain to fall in southern India and Sri Lanka.
There is also signs of some equatorial Rossby Wave activity over the region during the first half of January, which should also help with rainfall in southern India and Sri Lanka. All these signs lead us to believe that much of Tamil Nadu, Kerala and perhaps southern Karnataka in India as well as Sri Lanka should be wetter than normal through at least the middle of January.
Model data on the right is courtesy of the JMA
Looking ahead to later in January, rains may ease during the second half of January, but the third and fourth weeks of the month are still expected to average at least close to normal as far as rainfall. There is a good chance the third week of January can still be on the wetter side of normal as the ECMWF and CFS weeklies suggest.
Many global climate models, as shown above, support our idea of wetter-than-normal January across much of southern India and Sri Lanka. Rainfall may return to more typical levels across these areas in February, but Sri Lanka could remain in the wetter-than-normal pattern into February.
Report a Typo