The Hindu Business Line : Bay continues to be put under storm watch

Thiruvananthapuram, Oct. 7 The Climate Prediction Centre (CPC) of the US National Weather Services has retained a close watch on the Bay of Bengal for signs of ‘intense tropical activity’ during October 14-20.

Monsoon transition from the southwest to northwest takes place during this time marked by reduced vertical wind shear, which otherwise kills developing storms. Wind shear (sudden change in direction and strength) is the highest during a monsoon and systems grow to the level of a depression/deep depression only.

October is a favoured time of the year for tropical cyclones when the monsoon relaxes, the CPC said. Apart from the Bay, the Gulf of Mexico is the only other ocean body kept under watch for cyclogenesis. The enhanced convective phase of a periodical Madden-Julian Oscillation (MJO) wave increases the threat of tropical development in the Bay.

WIND DIRECTION

The Global Forecast System (GFS) model showed clearly that wind direction at the surface level may start turning from southwest to east-northeast during the five-day period from October 11-15. The monsoon southwesterlies are now on a steadily weakening trend.

Speaking to Business Line, Dr Akhilesh Gupta, Senior Advisor to Department of Science and Technology, said the GFS observations are in line with what are considered normal for this time of the year.

The cessation of the lingering rain activity in the east and northeast India provides the trigger for the monsoon transition. The seasonal trough (Inter Tropical Convergence Zone or the ITCZ) yanks itself from its current alignment into the south peninsula.

The ITCZ is a global band of low-pressure and where tropical storms are harvested from time to time. During October, storms get generated within the Bay basin (in situ), grow out of stray circulations from neighbouring seas or get thrown up by the accentuation of easterly waves.

ANTI-CYCLONE

The jumping of places from the north to the south would also nudge the large but laggard anti-cyclone into place in the northwest, Dr Gupta said. The size of the anti-cyclone impedes its own movement; but the two other seasonal features in transition – the ITCZ and the monsoon – allow the massive system some room to find its moorings.

On Tuesday, India Meteorological Department said that the scattered rainfall activity over West Bengal, Sikkim, north Orissa, the Northeastern States would persist for three more days.

Parts of south peninsula too would receive rains during this period, but international models suggested that they may persist even beyond, before merging with an incoming wave of rains progressing from the equatorial Indian Ocean.

PENINSULAR RAIN

The US-based Centre for Ocean-Land-Atmosphere Studies saw rains getting more pronounced to west-central and adjoining south peninsula during the week ending October 14.

The subsequent week would see thunderstorms clustering around the peninsular tip and Sri Lanka to the south. It is expected that the northeast monsoon would have got well and truly under way by this time.

More Stories on : Climate & Weather | Climate & Weather

Article E-Mail :: Comment :: Syndication :: Printer Friendly Page