Monday, November 02, 2009

Core of N-E monsoon rains biding time to enter mainland

Most of the northeast monsoon rains are still falling largely over the open seas around the equator where elevated sea-surface temperatures and resultant convection have thrown up cloud masses across a large area from west to east.

The Madden-Julian Oscillation (MJO) wave is locked in over this belt as can be inferred from the negative outgoing long-wave radiation (OLR) values, a proxy for cloud cover.

Model predictions are of the view that the northward migration of the MJO wave and the cloud cover into southeast Arabian Sea and southwest Bay of Bengal would begin from mid-week this week.

May move north

The cloud cover is forecast to hang over these parts up to November 19 according to the Wheeler MJO tracker, while the Jones model and the Empirical Wave Propagation method of US National Centres for Environmental Prediction (NCEP) saw the wave effect dissipating a few days earlier.

This phase would likely see the whole of the peninsula receiving rains, to the calibrated move north of a weather system over the southeast Arabian Sea along the Kerala coast.

In fact, the European Centre for Medium-Range Weather Forecasts (ECMWF) sees the possibility of a 'low' springing up over southwest Arabian Sea tracking north along the Kerala coast intensifying into a cyclone.

It is forecast to make a landfall over the north Konkan-Mumbai-south Gujarat belt around November 11. But meteorologists are of the view that these are early days yet to take a call.

Arrival of intervening western troughs with opposing flows can decisively influence the formation, life and track of a storm developing over the peninsular seas during this time of the year.

But ECMWF visualises precisely this - a westerly trough trooping in but only to scoop the 'low' over Arabian Sea, allowing it to wheel along the west coast for a landfall over the Mumbai-South Gujarat belt.

Not agreeable

Two other cyclone evolution and tracking models, US Navy's NGP and the Canadian Meteorological Centre (CMC), did not agree and indicated that the 'low' may track northwest off Sri Lanka and park itself over central Arabian Sea by November 7 up to which forecasts were available.

The Roundy-Albany model continued to signal some weather activity over the southwest Bay off southeast coastal Tamil Nadu around November 11 but not to the level of intensity initially estimated.

The ECMWF precipitation forecasts seem to more or less agree with the outlook and show some 'unwinding' activity over northern Sri Lanka and southeast Tamil Nadu around this time.

As for the Arabian Sea, this model shows concentrated rains over central and west-central Arabian Sea (away from India coast) tracking the storm movement. This sits well with the storm movement track predicted by NGP and CMC.

Back home, an India Meteorological Department (IMD) update said that the northeast monsoon has been active over Tamil Nadu during the 24 hours ending Sunday. Cold wave conditions prevailed at isolated places over north Madhya Maharashtra.

The Regional Met Centre, Chennai, said that rainfall occurred at many places over coastal Tamil Nadu and at a few places over interior Tamil Nadu and Kerala during this period. Isolated rainfall occurred over Lakshadweep.

Heavy rains

Among stations recording very heavy-to-heavy rainfall (in cm) were: Puducherry airport -16; Sirkali and Cherthala (Kerala) - 9 each; Pamban-6, Karaikal, Tiruchi and Nagapatinam-3 each; Coonoor, Minicoy, K. Paramathy and Thanjavur-2 each.

Forecast until November 3 said 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 and Lakshadweep.

Isolated rain or thundershowers are likely over south coastal Andhra Pradesh, Rayalaseema and south interior Karnataka.

Isolated heavy rain is likely to occur over coastal Tamil Nadu and Puducherry during the next two days, a warning issued by the Chennai Met Centre said.

1 comment:

  1. Will 2009 northeast monsoon be vigorous over tamilnadu, will it cover drought hit interiors? Seems very weak monsoons. Yesterday's low pressure over southeast Arbian Sea seems to turn anticlockwise into southeast bay. But now low pressure seems to move towards Bangladesh. So another dry season for drought hit Tamilnadu. If low pressure would have turned clockwise then Maharashtra and Gujrat would have got cyclonic rains. Already Gujrat and Maharashtra had enough voilent rains from southeast monsoon. Question is why is Northwest monsoon avoiding Tamilnadu?
    For dry tamilnadu to become wet it should rain atleast 3-4 months nonstop. It is not strong like in Mumbai where at times it rains 600mm-1000mm in 24hours non stop for months. Also weather patterns is changing, central india - Maharashtra, Gujrat-Saurashtra are receiving more rains while south - Tamilnadu, Rayalseema, Karanataka are slowly turning dry and desert like condition. I hope our scientific models will do some more analysis or weather prediction models should undergo a change. Is it problem of acute deforestation and no trees? Strange part of this 2009 northeast monsoon is clouds tend to move below Sri Lanka and drift over to Africa. This is due to no low pressure over tamil nadu to pull clouds up. May be an artificial or man made pull is required like cloud seeding. Temperatures were consistently high in 40's for september and october if natures makes twist it may continue for november. Also we see no cyclonic formation over the bay.