The Hindu Business Line : Arabian Sea arm of monsoon catching up fast

The southwest monsoon has progressed into more parts of the Southeast and Southwest Bay of Bengal, the South Andaman Islands and most parts of the Andaman Sea.

Conditions are favourable for its further advance into the East-Central Bay within the next 24 hours, says a forecast put out by the National Centre for Medium Range Weather Forecasting (NCMRWF). Moisture is building continuously, lower level wind flow getting stronger and large-scale rainfall activity becoming persistent over South Bay of Bengal and the Andaman Sea region into the weekend.

The Bay of Bengal arm of monsoon will then cool its heels, with the focus then shifting across the peninsula and into the west where the Arabian Sea arm would have set its sights on the much-awaited foray into the southwest coast of the country.

Speaking to Business Line, Dr Akhilesh Gupta of the NCMRWF said at least six major MJO (Madden-Julian Oscillation) models have clearly indicated the evolving roadmap for the annual spectacle. The MJO is an equatorial pattern of anomalous rainfall that travels to the east in cycles of 30 to 60 days.

Wet phase

The MJO has a wet phase of enhanced convection and precipitation followed by a dry phase where convection is suppressed. Strong MJO activity is often observed during a weak La Nina year or an ENSO-neutral year, such as the ongoing one.

Explaining, Dr Gupta said the Outgoing Long-wave Radiation (OLR) anomalies coupled with the wind anomalies at the 800 millibars level (at a height of 1.5 km) suggest that favourable conditions for onset of monsoon over the Kerala coast should establish anytime during the week beginning Wednesday next. Several dynamic and statistical models are in agreement with this outlook.

The cross equatorial flows that carry the moisture feed from the southern hemisphere are seen strengthening from Wednesday. Wind speeds over the Bay of Bengal could possibly clock up to 70 kmph, which supports ideal monsoon conditions.

Clear indications

By the next day, the flows will convert themselves into the Westerly Jet, reaching out into the Central Arabian Sea. This would be the clearest indication of an approaching onset of the monsoon. .

This is supported by concurrent accentuation of the Inter-Tropical Convergence Zone, a band of cloudiness close to the Equator, resulting in large-scale cloudiness and rainfall activity over South-Central and South-East Arabian Sea in subsequent phases.

Meanwhile, heat wave conditions have abated from Rajasthan. Day temperatures are two to five deg below normal over the plains of Northwest India, Uttar Pradesh, Northwest and East Madhya Pradesh and Chhattisgarh.

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