The Hindu Business Line : Arabian Sea depression set to intensify

Thiruvananthapuram, June 5 The US Navy Joint Typhoon Warning Centre (JTWC) has upgraded the potential for formation of an Arabian Sea cyclone as ‘good’ on Friday/Saturday.

An India Meteorological Department (IMD) update said that the ‘low’ in east-central Arabian Sea had concentrated into a depression (two notches below cyclone status) and lay about 800 km southwest of Mumbai on Thursday afternoon.

It warned of strong surface wind speeds reaching 45-55 km/hr along the west coast during the next 24 hours. Fishermen are advised not to venture into the sea.

Long in making

Model runs globally have been suggesting ‘cyclogenesis’ in the Arabian Sea for quite sometime, given the strong flows boosted by a seasonal Madden-Julian Oscillation (MJO) wave of anomalous rainfall across the Indian Ocean.

JTWC satellite imagery showed deep convection developing near a consolidating low level circulation center (LLCC, the nucleus). Strong low-level flows and a good ‘window’ effect towards the top will aid the intensification of the LLCC. Importantly, it is tracking steadily toward an area of lower vertical wind shear.

The IMD too expected the depression to intensify further but to move in a north-westerly direction. International models suggested the track will straighten later to being northerly, generally aiming Sindh in Pakistan and adjoining Gujarat in India.

The automated tropical cyclone forecasting system at the US Naval Research Lab, Monterey, sees the system (‘99A Invest’) intensifying into a cyclone (to be named ‘Abe’) by 5.30 a.m. IST on Sunday (June 8).

It will initially feature an outermost ring of gale-force winds (above 62 km/hr) and an inner ring clocking 93 km/hr. Later in the day, the system would start re-orienting towards slightly east to being largely northerly.

To intensify

The cyclone will undergo a round of intensification on Monday, adding a third concentric ring of still faster winds (118 km/hr) to its inner core. It will stay as such until 5.30 p.m. the same day, before weakening a bit.

On Tuesday, up to which forecasts are available, it is shown to move into the 22 deg N latitude in the northeast Arabian Sea to the south of Sindh and southwest of Saurashtra in Gujarat. The system should continue to move north unless acted upon by intervening forces, and make a landfall somewhere over Sindh.

This is a scenario that has been consistently forecast over the past week or two by the Roundy-Albany experimental cyclone prediction system. But it shows an intense ‘low’ system sitting smack over Gujarat until June 17 and being fed by moisture feed from an incoming ‘low’ from the Bay of Bengal.

The Noida-based National Centre for Medium Range Weather Forecasting (NCMWRF) has already predicted on Thursday that a preparatory cyclonic circulation is likely to spin up over the Head Bay during the next 24 hours. The north-eastern States are likely to experience widespread rainfall activity with heavy to very falls during the next three days.

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