After a two-week delay, the monsoon is finally progressing northwards, and has covered most parts of southern, central and eastern India. The monsoon has reached Maharashtra, Andhra Pradesh, Telangana, Chhattisgarh, Odisha, and most of Madhya Pradesh.
However, it is still bringing less than expected rainfall. For the month of June so far, the rainfall over the country as a whole has been deficient by 36% compared to what is normal until this stage. This deficit is unlikely to be made up in any substantial manner in the remaining days of the month. But the India Meteorological Department has predicted good rains in July and August.
During the onset phase over the Indian mainland, the monsoon currents were severely oppressed by the prevailing mid-latitude regime, forcing these currents to take longer to establish. Since the winter of 2018, there were strong and frequent western disturbances passing through much of the southern latitudes and altogether delaying the onset over Kerala. The continuous flow of strong western disturbances, too, made it difficult for the already weak monsoon currents to penetrate. As a result, the onset over the Kerala coast happened on June 8 instead of the normal date of June 1.
After that, the monsoon has progressed much slower along its western arm than along the eastern arm. This has been due to a number of reasons.
Soon after its onset over Kerala, the very severe cyclonic storm Vayu was formed in the Arabian Sea. As it progressed northwards, it hindered the advance of the monsoon which lay centred over Kerala for nearly a week. This, because the system attracted significant amounts of moisture from the southern peninsular regions and also from parts of Maharashtra, thereby slowing down the pace during the initial advancement of the monsoon.
Last winter, an Arctic burst had resulted in severe cold including sub-zero temperatures across the globe. The Indian southwest monsoon appears to be affected by some of its remnants, even in June. Meteorologists observed extra-tropical circulation prevailing over much lower latitudes over the Indian subcontinent and adjoining north Indian Seas (Arabian Sea and the Bay of Bengal) until a few days ago even after the onset of the monsoon over the Indian mainland. This resulted in conditions that were not supportive enough for the smooth inflow of monsoon currents blowing from the Arabian Sea, A K Srivastava, head, climate research pision at IMD,Pune, told The Indian Express.
Under normal atmospheric conditions, warmer northwestern regions and a relatively cooler equatorial belt facilitate and pull over the monsoon currents from southern hemisphere across the Arabian Sea along the western coast towards the land. However, this year, extra-tropical anomalies over the extreme northwestern region and the neighborhood left the entire region cooler, acting as a deterrent to the incoming monsoon winds. Besides, there was no low pressure system formed over the Arabian Sea that could have alternatively aided the monsoon progress along the west coast.
These, according to IMD officials, led to slower-than-expected progress of the western branch of the Southwest monsoon. Consequently, it did not bring significant amounts of rainfall over regions along the west coast. The otherwise heavy rainfall-experiencing areas including Kerala and Konkan-Goa remain rainfall-deficient by 35% and 54%, respectively, until June 26.
Contrarily, the situation with respect to the eastern branch of monsoon progressed faster, as a low pressure system formed in the Bay of Bengal fuelled for its swifter progress over the east and Northeast. On June 26, the northern limit of the monsoon currently was passing along Veraval, Surat, Indore, Mandla, Pendra, Sultanpur, Lakhimpur Kheri and Mukteshwar areas.
The late surge
The monsoon progress remained largely stagnant for nearly 10 days and stuck around south interior Karnataka and central Tamil Nadu until June 19. Thereafter, it made progress to some parts of southern Maharashtra on June 20The pace of its progress since then showcased a marked improvement as Maharashtra, along with all states in the Northeast, east, and south and some states in central India, were rapidly covered as on June 25.
As of June 26, the monsoon has fully covered Kerala, Lakshadweep, Tamil Nadu, Andaman and Nicobar islands, Karnataka, Andhra Pradesh, Telangana, Odisha, West Bengal, Assam, Nagaland, Mizoram, Meghalaya, Manipur, Arunachal Pradesh, Sikkim, Bihar, Jharkhand, Chhattisgarh, Maharashtra and partially covered Uttarakhand, Uttar Pradesh, Madhya Pradesh and Gujarat.
With the monsoon in its active phase rainfall intensity between light and moderate spells the countrywide rainfall deficiency as of June 26 stood at 36%. In other words, the actual rainfall of 86.3 mm is 36% lower than the normal of 135.6 mm for this time of the year.
IMD subpision-wise, Andaman and Nicobar (66%), East Rajasthan (32%) and Jammu and Kashmir (25%) have so far received above normal rainfall this season and have been categorised under the excess rainfall category. North Interior Karnataka (-1%) and Lakshadweep (-17%) have had normal rainfall. The remaining 31 subpisions have had deficient rain or none.
The monsoon is expected to strengthen towards the end of this month. Forecasts suggest the formation of a fresh low pressure system over the Bay of Bengal around June 29 or 30. This system will then send a fresh monsoon pulse that will help the further advancement of monsoon to the remaining areas along northwestern and Central India during July 1-July 3. The IMD has forecast heavy rains around July 2 and July 3 along the west coast, mainly for Konkan-Goa and north interior Karnataka.