Skymet sees monsoon arriving over Kerala by May 28

Private forecaster Skymet Weather has assessed that the 2020 South-West monsoon may make an onset over Kerala around May 28 (with a margin of error of +/- four days). The normal date of onset is June 1, but Skymet reiterated that the onset date has no bearing on its further advancement to other parts of the country. Peer private forecaster The Weather Company, an IBM Business, had said in its outlook issued in April that the onset could occur by May 31.

In its forecast, the India Meteorological Department (IMD) has said that the monoson will arrive over Kerala by June 5. Earlier, the IMD had revised arrival date over the Andaman Sea based on data from 1960-2019, and pushed it by two days to May 22. But the onset date for Kerala remains unchanged on June 1. Arrival of seasonal rains over the most of the central parts of the country has been delayed by 3-7 days, while they have been preponed over North-West India by about a week.

Heavy showers for Maldives

Meanwhile, the Maldives Meteorological Service has warned of fairly widespread rain with isolated heavy showers and thunderstorms over the country, which receives the monsoon on its way to the Bay of Bengal. Winds continue to from North-West/North at close to 10-26 km/hr over the Northern atolls but blow from South-West/West, which is monsoon-friendly at 24-40 km/hr elsewhere, gusting up to 72-80 km/hr during showers.

The normal monsoon onset over the country is mid-May, and model runs show the winds picking up further strength in tandem with the intensification of the low-pressure area in the Bay of Bengal.

The IMD has said that the low over the South-East Bay and adjoining South Andaman Sea has become well-marked, a step away from being called a depression. It may reach depression strength today (Friday) over the central parts of the South Bay and further intensify into a cyclone by Saturday evening.

Skymet Weather said that the low has been pushing the monsoon current, which may engulf the Andaman Sea to precipitate the onset by May 16-17. The storm in the making may take about five days to wind down in strength. The seas on either side of the South Peninsula may take a few days’ time to recoup the kinetic energy lost in the process. This could bring a lull in weather activity over Peninsular India for a few days.

Monsoon onset parameters

Skymet Weather recalled that  the monsoon onset over Kerala is announced based on fulfillment of specified conditions both over the ocean and land, ranging from wind direction, speed, depth of westerly winds, to cloud cover over the Indian Ocean in the proximity of the Comorin region.

Then there are rainfall amounts being recorded for two consecutive days at 14 named stations across Karnataka and Kerala, which remain the most important and primary requirement. The onset over Kerala has a standard deviation of seven days; which goes to mean that on 99 per cent of the occasions, the event occurs between May 25 and June 8.

In the last 10 years, the earliest arrival was on May 23 in 2009 and the most delayed on June 8, 2016. Currently, weather models indicate a strengthening of the cross-equatorial monsoon flows and the sea conditions supporting a fresh surge around May 25. A lag of 2-3 days thereafter is quite normal for the commencement of rains along and off the Kerala-Karnataka coast.

The monsoon would have already arrived over the Andaman & Nicobar Islands, Myanmar and Sri Lanka by then. Skymet refrained from issuing a monsoon long-range forecast this year saying it wanted to recalibrate its systems and resume the forecast from next year.