Friday, September 03, 2010

Why is Chickamaglur, Medikiri receiving less rains since last 5 years?

1. Though not five years, it is this SWM 2010 period that the catchment areas of River Cauvery is getting lesser rainfall.
You know that the mean latitude where the SWM will be active is about 15 degree parallel. But this year [2010] the cross equatorial flow in Arabian Sea is stronger in such a way it touched first Goa, Maha, Guj & Rajastan areas right from the early days of on set.
2. The traditional off shore trough that used to prevail in Arabian Sea from Lakeshawadeep to Maharashtra was mostly absent or seen in the upper latitudinal areas only.
3. Further the monsoonal winds were [& are too] stronger above 850 hPa level. This leads, many a times, the moisture laden winds to cross the western Ghats / penetrate Himalayas. Similarly, one of the attributed reasons for heavy rainfall in LEH area was also due to this.
4. The conventional monsoon trough from Ganga Nagar to Head Bay was not prominent most of the time.
5. Similarly monsoon depression in the Bay was less.
6. [As pointed out by some body]The traditional Easterly Jet at 13 Degree Latitude over Chennai that usually prevails in monsoon period [July] was weak or not prominent; instead the stronger monsoon wind that emerged from Arabian Sea get advected and became higher level easterly divergent flow to form (neat Tibet) a high pressure area. This easterly winds played important role in late August to drag clouds from east to west. Thus there were unusual heavy rainfalls in North Coastal Tamilnadu i.e Cholamandalam Coast upto and along 10 Degree, South Coastal AP, Rayalaseema, western MP,Delhi,Rajstan,Gujarat. 

Posted by Kaneyen
Probability of a good September monsoon ??...
3pm, Heavy showers over Uttarpradesh, N & N-E Madhyapradesh... and showers seen popping over Haryana...
RT @malhotramona: @weatherofindia mumbai weather pic 2... (3:55pm)
3pm, Showers along S. Andhra coast continues... while the cloud mass in Bay is getting weak...
RT @malhotramona: @weatherofindia a partly cloudy mumbai pic ... (3:52pm)
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.
RT @cnnbrk: Weakened Earl brushes NorthCarolina's OuterBanks, packs 105-mph winds
11:30am, We can see the Heavy cloud formation along S. Andhra coast and N. Tamilnadu coast.. due to the LOW ...
The Low is expected to weaken and then cross into N. Orissa on Sunday
The present Low is expected to deepen further in another 24hrs and move near to Orissa coast ...
As expected a LOW and circulation has formed over W-N-W Bay along N. Andhra coast ... ...
RT @rajugana: @weatherofindia, baroda 10.20am, Clear sky in the morning, but now dark passing clouds from SW.
RT @joesat: Heavy rain @ palavakkam (Chennai) since 2:15 am @weatherofindia hopefully get done by morning.