Saturday, November 21, 2009

North-East monsoon may get into `surge mode' again

The North-East monsoon is in a "surge mode" upstream of the Bay of Bengal with high winds and heavy rains warned of in the Gulf of Thailand over the next two days.

This is being triggered by the massive seasonal high-pressure area covering China now extending a "limb" south into mainland Thailand compressing the north-easterly flows over the Thai Gulf and the Malacca Straits.


Even otherwise, the ground setting for the surge was more or less complete with the arrival of the Madden-Julian Oscillation (MJO) wave, very warm seas and intense convection across an area stretching west to the Bay of Bengal and reaching the Sri Lankan and Indian coasts.

The MJO wave travels in the upper levels and sets off weather activity or magnifies existing weather over ground. The wave moves west to east, and had been active over equatorial Indian Ocean until now.

Meanwhile, the Thai Met Department has warned ships, especially small boats, sailing through the Gulf and the adjoining Andaman Sea to exercise caution over the next two days, given the monsoon surge.

It is likely that the disturbed weather may get propagated into the southeast Bay of Bengal from across the Thai peninsula over the very warm waters (up to 31 deg Celsius).

On Friday, the Thai Met Department saw a cyclonic circulation each over the southern tip of India as well as half-way down to the east-southeast. India Met Department (IMD) too traced a cyclonic circulation lying over Kerala on Friday.


The European Centre for Medium-Range Weather Forecasts sees a churn being set off over south-east Bay of Bengal and Andaman Sea during the next week and getting propagated to the west in phases.

The system will grow in intensity by Nov 29-30, and may reach depression status over south-central Bay of Bengal and would be positioned to hit north Tamil Nadu-south coastal Andhra Pradesh coast.

Further strengthening of the system would depend on the prevailing sea-surface temperatures, which are currently cooler side towards the Indian coast.

The US National Centres for Environmental Prediction (NCEP) supports this outlook by suggesting a wet regime for the entire southern peninsula during November 20 to 27 with concentrated rains forecast for Tamil Nadu and Sri Lanka coasts.

The NCEP expects to see this wet spell lingering through the following week (Nov 28 to Dec 6) as well, especially along the Tamil Nadu coast.

IMD observations on Friday also talked about the presence of a trough of low (not amounting to a low-pressure area) over southwest Bay of Bengal and adjoining Sri Lanka. This is an extension weather of the brewing disturbed weather over upstream Andaman Sea and the Gulf of Thailand.

The Chennai Met Centre said in its update that rainfall occurred at many places over Kerala and coastal Andhra Pradesh and at a few places over coastal Tamil Nadu and south interior Karnataka during the 24 hours ending Friday morning.


Isolated rainfall was reported from interior Tamil Nadu, Rayalaseema, Telangana, coastal and north interior Karnataka.

Forecast for the next two days said that rain or thundershowers are likely to occur at many places over coastal Tamil Nadu and Puducherry and at a few places over interior Tamil Nadu, Kerala, Lakshadweep, coastal Andhra Pradesh, Rayalaseema and coastal Karnataka.

Isolated rain or thundershowers are likely to occur over interior Karnataka and Telangana.

A warning valid for the next two days said that isolated heavy rain is likely over coastal Tamil Nadu and Puducherry.

Towards the north, minimum temperatures are likely to fall by 1-2 deg Celsius over northwest India and by 2-4 deg Celsius over central and adjoining east India during the next few days.

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