The Hindu Business Line : Winds, humidity levels fail to measure up

Thiruvananthapuram, May 30 Light to moderate showers were reported from most places in Kerala from Thursday evening in what is widely being thought to be the run-up to the onset of the southwest monsoon.

Two of the dramatic changes associated with the onset are the rapid increase of the daily precipitation levels and rise in the vertically integrated humidity over the monsoon region.

But on Friday, lower-level southwesterlies and the upper-levels easterlies had not settled into their rhythm. Humidity levels too had failed to build to adequate levels – only 64 per cent in Thiruvananthapuram, 72 per cent in Kozhikode and 74 per cent in Kochi.

SET TO IMPROVE

Forecasts for the next 24 hours bespeak marked improvement in the wind behaviour. This is expected to strengthen the shear zone of monsoon turbulence over the southern peninsula. The persisting trough of low at sea level from west central Arabian Sea to southwest Arabian Sea is a helpful feature.

The offshore trough from the Karnataka coast to Kerala coast was also traceable. Cyclonic circulations hovered over the Lakshadweep area as well as over south Tamil Nadu and adjoining Commorin. Over land, a trough ran down from Vidarbha to north interior Karnataka through Marathwada.

According to the Global Forecast System (GFS) of the US National Oceanographic and Atmospheric Administration (NOAA), the onset could take place during the five days ending June 2. This is based on the surmise that the southwesterlies would work up good speeds during this period and stay as such until June 7.

The easterlies are also seen holding strong; still, the monsoon current is not seen reaching Mumbai at least until June 6. By June 13, though, it would have covered the two-thirds of the landmass to the south and southeast, according to GFS forecasts.

UNDER WATCH

Meanwhile, the US Naval Research Lab at Monterey and the Joint Typhoon Warning Centre (JTWC) continued to keep a tab on the area of convection (`98A Invest’) some 1,200 km to the southeast of Mumbai for signs of intensification. On Friday, they promptly ruled a cyclone formation alert during the next 24 hours at least.

An India Meteorological Department (IMD) update said on Friday that rain or thundershowers are likely at many places over Lakshadweep Islands, coastal Karnataka and Kerala over the next three-four days. Isolated thundershowers are likely over the rest of the region.

A prevailing western disturbance over Jammu and Kashmir and the barrage of northwesterlies featured a couple of cyclonic circulations over west Rajasthan and Punjab.

THUNDER SQUALLS

These would combine with a north-south trough over Pakistan to trigger isolated rain or thundershowers and thunder squalls over northwest India during next few days. This could only distort the heating process over the landmass with implications for orderly progress of monsoon into these parts.

On Friday, heat wave conditions prevailed anomalously over some parts of coastal Andhra Pradesh and at isolated places in Vidarbha and north coastal Tamil Nadu. The seasonal “heat low” over west Rajasthan has been jeopardised in this manner.

The `heat low’ sets up the ideal pressure gradient along which the monsoon drives into upcountry regions. But forecast valid for the next few days for Rajasthan indicated the possibility of dust storms or thunder storms in the State.