Tuesday, October 23, 2007

My apologies for not updating this blog for the last 10 days. Was away, and unable to keep in touch with the latest on the sub continent weather, and unable to answer to reader's comments.

Finally, this year's unpredictable south-west monsoon has widhrawn ! Since its setting, the monsoon has been erratic, and often proved the weatherman wrong, and quite a few times totally misled the predictions.

Today, the IMD has declared the widhrawal of the south-west monsoon from Goa southwards across the entire country, in one day. And "Simultaneously Northeast Monsoon rains have commenced over Tamil Nadu and adjoining states of south peninsula." Quote IMD.

The W.D. moving across the north, was the main culprit for the delay, as it produced stray showers in the east and north-east, and the prevailing south-westerlies prevented the monsoon from totally moving out. But, with the system moving away eastwards, the high pressure anticyclone has quickly taken control, and organised the north-east flow in a more systamatic pattern (IMD streamline).

Moving to the north-east monsoon, it is clear that the China Sea, is still in an active phase, and is expected to pulsate a low in the south bay around 24th. October. According to weather models, and Jim Andrews of Accuweather, this low could form into a depression and cross the TamilNadu coast around the weekend. Some other forecast models predict the system to cross the east coast and re-emerge into the Arabian Sea. GFS from COLA shows the system crossing the Tamil Nadu coast around the 26th. and the rain area spreading and subsequently covering the entire southern Peninsula as the system weakens. And in fact, the rains are seen reaching as far north as Mumbai around 27th./28th.(check at http://www.monsoondata.org/wx/india.vv.html).

Personally, I tend to agree with this, as the Arabian Sea may not be conducive to revive a system, as it may not be stronger than a depression at the time of crossing the east coast.
But, surely there will be enough heavy rains along the Tamil Nadu coast, and in the interoirs of the southern states. Kerala, can get heavy rain around middle of next week, as a vortex may form in the south Arabian Sea, as the depression crosses the coast.

With the West Pacific regoin still active, I expect more depressions to come along the bay path, and keep the north-east monsoon vigourous in phases for at least another month till mid November. After that , the feeding from bay systems can cease, and the focus will shift to the strenght and frequencies of the W.D's in the north, as that too will have a direct impact on the frequencies of occurances of the easterly waves from the bay.
Due to the IRI predictions of a strong La Nina during the Oct/Nov/Dec period, the rain forecasted for the same period is above normal for the southern Peninsula, hence indicating a weaker flow of W.D's in the northern regions of India and Pakistan.

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3 comments:

Anonymous said...

hi Rajesh,

reading your post after a long time. Yeah, The N.E.Monsoon has set itself in Tamil Nadu. The southern region are having the heavy falls aroud 12 - 15 cms. The place in and around chennai are having sporadic showers for the last 3 days, nothing significant.

Also need to ask you about the report from chennai weather center

http://www.hindu.com/2007/10/18/stories/2007101855541300.htm

La Lina acts as a detterent to the N.E.Monsoon and El Nino for S.W.Monsoon

Anonymous said...

hi Rajesh,

reading your post after a long time. Yeah, The N.E.Monsoon has set itself in Tamil Nadu. The southern region are having the heavy falls aroud 12 - 15 cms. The place in and around chennai are having sporadic showers for the last 3 days, nothing significant.

Also need to ask you about the report from chennai weather center

http://www.hindu.com/2007/10/18/stories/2007101855541300.htm

La Lina acts as a detterent to the N.E.Monsoon and El Nino for S.W.Monsoon

rajesh said...

As i mentioned, the La Nina effect may give excess rains in the extreme south. Otherwise rains for the north-east monsoon should be around normal, not above normal, i think.And, it there is no direct or definite link of the monsoon with La Nina.