Saturday, May 29, 2010

IMD sees monsoon onset ‘around Monday'

India Meteorological Department (IMD) has said that the onset of southwest monsoon over Kerala would occur ‘around May 31'.
The IMD had, on May 14, issued the forecast for onset of monsoon over Kerala on May 30 with a model error of 4 days.
It based its latest outlook on interpretation of latest meteorological conditions and also guidance of numerical weather models.

There is also good possibility for the development of a monsoon onset vortex (a small but intense low-pressure system), off the Kerala coast during this period.
But the movement of the vortex is predicted to be away from the west coast, in a north-northwesterly direction, the IMD said.
(Numerical weather model predictions seemed to suggest rapid development of this system into a likely cyclonic storm.
These predictions showed the system spinning away into the west-northwest direction but posited half-way into north Arabian Sea by June 4 up to which forecasts were available.)
Westerlies may strengthen
It is expected that the vortex would help strengthen the southwesterly winds along the west coast, the IMD said.
Numerical models indicate possibility of strengthening of the cross equatorial monsoon flow along the Indian longitudes.
The IMD operational models also show strengthening of lower level westerlies with increase in depth, northward extension and quantity of moisture content along the west coast.

Models are indicating development of organised convection over the South Arabian Sea from Sunday onwards.
Referring to two major monsoon facilitators, the IMD said that the ‘heat low' has established over the northwestern parts of the country.
In this manner, the north-south pressure gradient (high in south to low over northwest) has strengthened, particularly over the Bay of Bengal.
There is also possibility of further advance of monsoon up to coastal Karnataka and southern parts of Tamil Nadu by around June 1.
Forecast from various global models indicates better circulation features conducive for monsoon during June 4 to 10 with strengthening of the cross equatorial flow over south Arabian Sea.

Models are also indicating increase of rainfall over the west coast of India during this week, the IMD outlook said.
Under these meteorological conditions, there is also possibility of advance of monsoon up to south Konkan and Goa along the west coast and also over parts of the Northeastern States.

Meanwhile on Friday, satellite pictures made available by the US National Weather Service at 5.15 p.m. showed convection mostly concentrated to east-central Arabian Sea.
Some of the clouds streaked across adjoining east and southeast Arabian Sea reaching into Kerala and adjoining south Arabian Sea.
A number of international models had already hinted the cyclogenesis in the Arabian Sea over the next few days, close on the heels of monsoon onset over Kerala coast.
Some of these models suggested a changed track for the brewing system, which could first approach the Kerala-Karnataka coast initially.
The system might just toy with the coast by May 31-June 1, before shifting gears and start tracking north along the west coast.
It would then start re-curving north-northwest as models suggested earlier, and head into the north Arabian Sea by June 4.
But from here, models tend to disagree with the likely track of the storm in view of the arrival of a westerly trough from the northwest that would cut across Pakistan into north Arabian Sea.
The European Centre for Medium-Range Weather Forecasts (ECMWF) has in its update on Friday suggested that the westerly trough would ‘appropriate' the storm and steer it towards the east.
This was the case with Cyclone ‘Laila' that hit the Andhra Pradesh coast last week, before being steered north-northeast by a passing westerly trough that dipped into central India and adjoining Bay of Bengal.
In this manner, the ECMWF forecast template, the farthest available on Friday, took the system tracking to the east from north Arabian Sea for a likely landfall over southwest Gujarat by June 7.
The agency had initially suggested that the system would continue to track north-northwest and cross the Oman coast in a replay of year 2007 when Super Cyclone Gonu.

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