Thursday, April 30, 2015

Monsoon Watch - 3.. 2015 ....Part 1....30th April 2014..

1. ENSO:

Subsequent to writing the MW-2, we are keeping a careful watch on the El-Nino developments. Sea surface temperatures now exceed El Niño thresholds and trade winds have remained weaker than average for several weeks. This suggests some coupling between the ocean and atmosphere may be occurring. If these patterns persist or strengthen, El Niño will become established.
But, (SOI) has become less negative over the past two weeks, with values returning to neutral bounds. The latest 30-day SOI value to 26 April is -3.6

The heating does not seem to be happening at a faster rate or in a hurried manner. The last 2 weeks heating 

Niño 4       1.3ºC
Niño 3.4    1.0ºC
Niño 3       1.0ºC
Niño 1+2   1.5ºC

The majority of the models indicate Niño 3.4 SST anomalies will remain greater than or equal to +0.5C through the end of 2015


The most recent ONI value is 0.7c...(El Nino is characterised by ONI values of 0.5 or above, La Nina is characterised by -0.5 or below).


May happen that an eventual El Nino, though unavoidable, may actually form full fledged (around End July/August) the latter months of our South West Monsoon. South West Monsoon may get sluggish ( In Peninsula) after July, around August and September. Can get stronger in Northern Pakistan after August.


Indicator: -ve, as El Nino chances possible in Latter Months of Monsoon.


2. Sub-Continent Seasonal Low: 


With every passing WD, (A-6 just moved away), the seasonal Low gets a set back. But things are taking shape slowly. The seasonal trough (eastern wing) could start forming in Northern Thailand in first week of May


Seasonal Low has shown good signs of forming, core pressure at 1000 mb...

The seasonal low in the Thar region is now very weak.The pressure around the Thar desert region is now 1000 mb (994mb required by June beginning). Proper central core is forming now. And ,as per the required scheduled development, a proper gradient should be in the making.


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Days temperatures have "performed miserably" in the MW-1/MW-2 inter period ! Below normal day temperatures by as much as 13c had been recorded, and the highest on date in the Sindh areas is 48c. In India , it has reached 45c in Rajasthan.

Again, snow and rains in the Northern hills. 


As a result, and expectedly, the day temperatures fell, and the seasonal low was almost wiped out. Heating trend started in late April though.


See the trend in April for Delhi, Bikaner and Jacobabad.





An exception this year is the Vidharbha region. Even without the normally exceptionally heavy rains, the temperatures in Rajasthan and Vidharbha are just about managing 42/44c (till end April), and in some cities just hovering around the low 40s. 
Highest yet was 45.5c in Jaisalmer on 27th April. Normally Vidarbha is a hotbed ! 45-47c is a "kid's playground" for the region.
Nagpur trend in April.


The minimum temperatures this year, have touched 33c in Sibbi on 26th, 31c in Rohri Pakistan on 30th. 
In India, a minimum of 30c or above is yet to be achieved.

In 2011, the minimum temperatures in the region  were higher comparatively at this time. Minimum temperature touched 30c for the first time in 2011 on 29th April at Kota (Rajasthan). 

In 2010, 30c as minimum was recorded on 17th April.

The maximum and minimum temperatures have to rise now in Sindh, Balochistan and North India. Trends of rising temperatures may be seen again  in Vidharbh, Gujarat and adjoining regions of Sindh.


True, the entire sub-continent region has to suffer a heat wave, but the gains are much more.  


The line of wind dis-continuity, currently is located, as a weak trough, in the centre of Southern Peninsula, South of  15N towards the tip of India. This LWD should strengthen, in the centre of the Southern Peninsula region. 

Out breaks of pre- monsoon thunder showers are expected normally in the southern states and South Maharashtra.  Though the showers in the South are heavy. We need the thundershowers to commence and precipitate in Maharashtra and Interior Karnataka, indicating a proper flow of moisture into the peninsula region. 

A LWD in the central peninsula region "looks after" the moisture content in the interior areas, and prepares the atmosphere with the humidity required fro a proper and good rainfall in the Lee ward regions.


Indicator: -ve.


3. Bay Low:


Continuing from MW-2, "Bay of Bengal" low pressure parameter is a worrying factor. Normally, the Bay should host a pre-Monsoon low any time after 15th.April. 


Like I mentioned in the previous MW, in 2011 we had a cyclone in the Bay by the third week, and in 2009 a cyclone crossed the Bay on 12th April.2012 hosted a low around 25th April (BB-1).

As on today, this region still maintains a luke warm response to the formation of a quick low. The pressure is anything but low, and the winds indicate a weak "high" trying to stabilise itself. 


What is needed now is a pulse from the Far East, to start with, and break up the existing high pressure area. Currently no Storm or Low pressure in the Philippines Seas.


MJO has entered a weak phase in our seas. The MJO turns negative in the Southern Bay areas after 29th April. MJO wave gets slightly positive in Bay around 18th May...seems suitable for the Monsoon there ! MJO may turn Neutral after 8th May in the Arabian Sea sector.

The shading indicates outgoing longwave radiation (OLR; W/m²).


Only +ve sign of a quick formation is that the SST is conducive. Map shows around 30c in the Bay and 31c near the Andaman Islands. Getting favourable temperature for  low formation.


Indicator: -ve

4. Cross Equatorial Winds : Indicator: neutral.


The Southern  high pressure region, the Power House of our Summer Monsoon, is constant down in the Southern Hemisphere, stretching off the Madagascar Island to the  mid South Indian ocean. 

The Mascrene Highs have maintained their strength, and i would say gained to some extent... at 1028mb. 


The cross equatorial wind flow, has just about picked up in the Western sector Southern Hemisphere. Winds, have not yet achieved the required speeds, but just  hitting the East African coast. To get a defined Somali Current, we need a proper re-curving Northwards/North-East of the winds, on the Kenyan coast. (Map)

However, The region below the equator in the Bay sector is almost in the same situation as MW-2.  In the Bay Branch, the Cross equatorial winds are perfectly diverted and changed direction towards SW after just crossing the Equator (Blue Arrows). But, in the Bay, the winds turn Southerly, and are dis organised along the East Coast of India.The winds hitting Sumatra coast (Green Arrow) are not Westerly (as  required), and also needs to gather strength soon.



Remember, the normal date for SWM to hit the South Andaman Sea is 15th. May.(Map)

In fact, a severe Cyclone Cat 4 " Quang" is "hanging around" the seas off the West coast of Australia...and expected to track SE towards Western Australia.

If no further systems form, we see ITCZ moving North, the High in the Southern Indian Ocean has a fair chance of getting stronger and anchoring well.


Indicator: Neutral.


5. The 200 Jet Streams too, show some awkward anomaly, in the last week.  Seems to be getting rectified only after 4th May. 

The 200 hpa Jet Streams:  core was located between Lat.26°N & Lat. 30°N with the wind speed varying between 81 kts & 109 kts around 200 hPa. The highest wind speed of 109 kts was recorded over Patiala on 20th April at 187 hPa

Conclusion: Indicators:  1) ENSO -ve  as El Nino chances possible in Latter Months of Monsoon.    2) Seasonal Low -ve     3)  Bay Low -ve  4)  Cross equatorial Winds Neutral. 5) UTH trough favourably forming around the Equator in the 80E -100E area.




Arrival of South West Monsoon:
I would put a slight delay in the South West Monsoon arrival dates for Andaman and Kerala as of now. 
But would like to wait for another 4 days to see any changes in parameters, so will put up MW-3 Part 2 on 4th May with proper dates of SWM arrival.

Then, we go into analysing the quantum of rainfall expected, in the subsequent MW-5 (which as usual will be in 2 parts), and will be ready for publication in May.


These views are of the Author. May not be used for Commercial purposes.

                                            End of Article...


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4 comments:

Tejas Baxi said...

Sir you write ..."Seasonal Low has shown good signs of forming, core pressure at 1000 mb...". Is "core pressure" different from MSLP? I saw many mslp charts but the lowest pressure i could find was 1004hpa.
please explain....
thanks

tejas

Raja Sekaran said...

This type of awareness was helful to the puplic and government.Thanks lot.

Kaneyen said...

Usually the surface pressure maps are in MSLP and are drawn at 2hPa interval. sometimes 4hPa interval charts are also drawn. While the outer lowest circle depicts the lowest pressure, the inner core will be lesser than that of the outer core pressure by say [2hPa or 4 hPa]

Odishanews Insight said...

Thank you for sharing this type of awareness..
Odisha News