Friday, September 03, 2010

Last week, we discussed the overall probability of a good September monsoon , with the forecast graph (which was put up then) showing good September rains.

Now, the situation remains hopeful, with Australian Bureau confirming the same. To reproduce from them :
"Over the past week, the MJO has progressed into Maritime Continent longitudes for the first time since May, and has contributed to the development of Tropical Storms "Mindulle", “Lionrock”, “Kompasu” and Namtheun” in the western North Pacific. Until now, tropical cyclone activity in the western North Pacific has been well below average; however the season lasts until December.
"The latest guidance suggests the active MJO will not spend long in the Maritime Continent region, but will begin to weaken over the coming week, and redevelop in the Indian Ocean towards mid-September. With this scenario, we would expect an increased risk of reinvigoration of the Indian Monsoon towards mid-September, and increased potential for tropical cyclone development in that region".

And, the SOI, an indicator of La Nina, was +17 as on 29th. August. A constantly +ve SOI , of more than +10 for 10/12 days indicates a La nIna phen

Coming to current situations, I would like to continue from where vagaries left off. As anticipated, rains (from the axis regions) have pushed into Delhi, Haryana and Utteranchal. Yesterday central M.P. saw good ranfall, and parts of western Gujarat/ Rajasthan too had rains (axis line regions). IMD picture shows rain distribution of 2 sept.

Due to an UAC formation (see map), clouds are seen of T.N. coast and South A.P. Chennai had some rains yesterday (Thursday), with the rain guage nothcing up 14.7 mms at Nungambakam and 5.7 at Meenambakam. Rains for not forecasted for T.N. coast earlier, as the UAC was expected to form off the A.P.coast. But on forming southwards, it has precipitated bonus rains in coastal T.N. Now, at least as per presumptions, the system will move North tomorrow and descend into a low off A.P. So, rains showers in Chennai till Saturday.
All models, including IMD forecasts now estimate a low to be formed in the Central Bay region tomorrow. The trough extending along the central bay, North to South, supports this cause (IMDMap).

Ok, the low should form and around 1000 mb should be of moderate intensity. Rainfall Friday/Saturday will be along the coast, near the system, and then move inland, into A.P.i estimate. But thence there are conflicting views of the system's movement. Some models predict rack into central India (M.P.) and fizzle out, in about 3/4 days. Others estimate not much deepening of the system, and fizzling out just on entering land in A.P./Orissa. ???

I would safely estimate the system to move inland upto west M.P. Rains along the path, as the system moves.
West coast will continue to receive the rainfall at the current levels, as the off shore trough "lives on" A little push from the system will increase rains in South Gujarat, near the gulf of Cambay, and adjoining Mah. coast on Saturday/Sunday.

Mumbai: The city received only 3 mms of rain on Friday. Periods of heavy showers on Saturday might increase the quantum to 15 mms/day on Saturday/Sunday. That is, a few more passing showers, with a cloudy day.

Rainfall total at Colaba: 3017 mms, short by 465 mms for target. Put in your opinion on poll.
Next blog on Saturday night.


nt said...

Thanks for the really detailed blog Rajesh. Being someone who does not understand the technical depths of things like 'MJO' I want to raise 2 issues:
1. Is the MJO behavior forecasted this time any different as compared to the previous years?
2. If a cyclone is formed in the Arabian Sea as forecasted my estimate is that will cause an abrupt end of the Monsoon as a lot of energy / clouds etc. will be pulled away by the system

Rajesh said...

nt, sorry for the late response.
Te MJO may not be different than previous years. Bcoz MJOs generally come in approx.15 days waves, waxing and waning.The timing this year maybe a bit late for a MJO wave in mid sept.
As yet no forecast is given for an Arabian Sea cyclone. Cyclone mentioned in Aust. report is for mid sept,or later, and could be in either seas.
Most of the Arabian Sea cyclones are post monsoon.

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