Will the monsoon reach Kerala on time?

On May 18, the monsoon reached the Nicobar Islands and within two days it arrived at the Andamans. As per the India Meteorological Department (IMD), at present, the Northern Limit of Monsoon (NLM) passes through the co-ordinates 5.0°N, 86.0°E; 8.0°N, 87.0°E; 13.0°N, 91.0°E and 16.0°N, 95.0°E which is represented by a green curve in the above image. 

Usually, we think that an on-time arrival of the monsoon in the Andaman and Nicobar Islands is a good and promising sign of not only an on-time arrival in Kerala but also an overall good monsoon rainfall. Of course, an on-time arrival in the Andaman and Nicobar Islands is a sign of "healthy" monsoon circulation but you never know when its health deteriorates. That is why there is no certainty of the monsoon arriving on time in Kerala if it has arrived on time in the Andaman and Nicobar Islands. In fact, there is no strong co-relation between these two events. 

According to the normal timetable of the monsoon, its next destination after the Andaman and Nicobar Islands is more areas in the Bay of Bengal and countries like Myanmar and Sri Lanka where it arrives on May 25. After that, its next stop is Kerala which is on June 1. But not many people know that at the same time, monsoon reaches parts of Tamil Nadu, Andhra Pradesh, Bangladesh, Meghalaya, Assam and Manipur. In fact, as per the above image showing the monsoon’s timetable, it arrives in Mizoram and Tripura before reaching Kerala. 

This time, the "pulse" of the monsoon seems to have gone down since May 20. Although it has continued to be active in the Andaman and Nicobar Islands, its progress seems to have been stalled. There isn’t any set of criteria for declaring the monsoon’s onset in Sri Lanka and Bay of Bengal. But meteorologists look for the onset signs which include sustained and well-distributed rainfall, strong westerly or south-westerly winds in a large part of the troposphere (lowest part of atmosphere where weather systems exist), cloud cover, amount of moisture etc. Weather models suggest the possibility of thundershowers in this week in some parts of Sri Lanka such as Colombo and latest satellite images show some clouds west of Sri Lanka. As a result, some forecasters are of the opinion that the monsoon will arrive in Sri Lanka on time. However, the distribution of forecasted rainfall in Sri Lanka isn’t proper and many areas such as the northern parts are expected to stay dry. The orientation of winds suggests that monsoon’s onset in Sri Lanka is going to be delayed by a couple of days and an onset around May 28 can be expected. 

Weather models also show increasing precipitation in parts of the Arabian Sea, Kerala and South India this week. Just like Sri Lanka, some are expecting the monsoon’s early or on-time onset in Kerala i.e by the end of May. 

This is contradicting with the onset window of June 3-11 given by IMD. So, how can the monsoon make an onset in Kerala at two times and on two different dates? This clearly means that one of these two dates is a "bogus" one while the other is a correct date. Let’s find out why the weather forecasters have been divided over the onset date which is confusing the citizens especially the farmers. 

A major mistake which we often make is that we think the monsoon is all about rain. There is a general tendency of attributing any rainfall event around June 1 (which is the normal onset date in Kerala) as a monsoon rainfall event. In many cases, presence of dark clouds and strong westerly winds, along with heavy rains, lead us to think that the monsoon has arrived. But one needs to understand that monsoon is an atmospheric circulation so the atmospheric components (such as wind speed and direction) are equally important. Hence, not every rain is monsoon rain. This is not the first year in which people are confusing between this type of rain (i.e pre-monsoon showers) and actual monsoon rain. In the past too, there have been many events during which it appeared as if the monsoon had arrived in Kerala, whereas in reality, it had'nt. 

A classic case took place on May 16, 1972 when IMD declared the monsoon’s onset in Kerala. Around this date, there were heavy rains in the region along with strong, near-surface westerly winds. However, very soon the IMD issued a correction stating that it wasn’t a proper onset but a temporary onset in the region. Then, on June 18, when the conditions became proper, the monsoon’s onset in Kerala was declared. In 1995 as well, monsoon-like conditions were observed in Kerala around mid-May but by the end of May, they disappeared. There have been at least six such known occurrences of temporary onset in Kerala which were during 1967, 1972, 1979, 1986, 1995 and 1997.