Further Analysis of the parameters as discussed in MW-1...
Position as on 21st April :
1.Cross Equatorial Winds:
Let me explain, that the winds on crossing the equator break into 2 branches. i) gushing into the Arabian Sea, and ii) moving into the Bay of Bengal.
Normal April Winds
During Monsoon Watch 1 , the cross equatorial flow was not at all organised.
i) The cross equatorial wind flow, has yet to organise up in the Western sector Southern Hemisphere. Winds, have not yet in the required SE direction off the East African Coast. The Northwards movement of the ITCZ will surely hasten and strengthen the winds.
ii) In the eastern sector, in the Bay Branch, the Cross equatorial winds are not organised Westwards towards the Sumatra Coast. Twin Lows at 5N and 5S above and below the Equator between 80E and 90E are kepping the cross flow winds dis organised. The winds hitting Sumatra coast are not Westerly (as required), and also need to gather strength soon.
And that is exactly where the start should be for the SWM to arrive at the Andamans. Upper winds at 100-400 hpa have just about vigorously starting in aiding the lower winds to attain the required direction and strength.
We prefer the Bay Branch to be better organised, as the SW Monsoon is normally expected there in 22-25 days…
Mascarene high pressure zones in the South Indian Ocean. Main High reading now 1027 mb and another one at 1018 mb has been observed between Madagascar and Australia.
The "Power House" of the Monsoon winds is slightly behind schedule, for this time of the season. But it is expected to strengthen fast with no tropical storms around.Hence would hasten the Cross Equtorial Wind flow.
Indicator : -ve
2. Seasonal Low:
No meaningful Heat wave is currently observed in the Sub Continent. By Heat waves, we mean temperatures over 5-7c above normal..not the normal heat.
The core low formation region(Thar desert/Sindh) has heated up normally this summer . The highest in the region of Thar /Sindh/Rajasthan has been around 44c, and Vidharbha Chandrapur just about touched 45c on 18/19th April.
See the 7 days Max temperature annomolly
In 2017, Barmer had approached 46 c and recorded min temp above 30 c. April heat records had tumbled at many locations in the subcontinent. On 19th April 2017, first ever 50 c temperature in April in Asia has been recorded at Larkana (Sindh).
Temperatures of more than 45 c had already been recorded in many states of India . Even at Srinagar (Kashmir),Shimla (Himachal) temperatures approached around 29 c in April 2017 . Delhi AP was 44.9 c on 20th April 2017.
Last year , in 2017, Most of India was in the 4-7c above normal range and pockets shooting to 15 c above normal ...
Earlier than normal,the night temperatures had also crossed the 30c mark ! Barmer in Rajasthan recorded 30.4c as minimum on 15th April ,Kurnool (Andhra) saw a low of 31 c on 19th morning and Jhansi (UP) saw a low of 31.6 c on 21st morning.
Jaipur,Kota,Bundi,Alwar,Bikaner,Churu,Pilani (Rajasthan), Cuddapah(Andhra) saw lows of/above 30 c on 21st April 2017 morning.
Comparison with previous years shows the difference this year. In 2010, the first 45c touched on 10th. April, and on the same day Nagpur was 44c, Delhi 42.8c. Soon on 15 th April 2010, Nawabshah (Pakistan) soared to 47c, Simla to 28.2c on 16th, Ganganagar, Akola and Hissar to to 46c.
But, in 2011, 2012, 2013 and 2014, till date, temperatures were yet to reach 45c anywhere in the Sub-Continent .
2015...Into the 3rd. week of April , we had seen 48c in Pakistan on 19th April in Larkana,and 46.5c in Moen Jo Daro. In India had just topped 44.6c in Barmer on 19th April.
2016....touched 46c in Bankura on 16th April...and was constantly hot in Eastern region with almost daily ,a place touching 46c.. Bhubaneshwar and Titlagarh in India and Dadu in Pakistan had touched 46c. Several large regions in Vidharbh, Telengana and MP were in the 44/43c range.
The seasonal Low, as a result of nominal heating, is shaping up "casually". It has shown slow progress after MW 1 when it was 1008 mb.
Last 2 days, the lowest pressure, in the core (Thar Desert) region was at 1006 mb.(Last year 998/1000 mb). (In 2011/2014 was 1006 mb, 2010/2012 was at 1002 mb this time. 2015/2016 it was at 1000-1002 mb).
As mentioned, it normally should reach a low nadir of 994 mb in June in the Thar Desert, and with 1008mb in the South Arabian Sea, a perfect gradient is created to attract the south -west winds towards the coast.
Thunderstorm activity in Southern Tibet is seen to be picking up.
The Line of Wind Discontinuity should normally stabilise around Central India perpendicular down into the Southern Peninsula by mid April.
This enhances the speed of the Seasonal Low formation. Normally is required to start taking shape for the monsoon by the second week of April.
LWD (trough) is currently near the Central-Southern region of the Peninsula…running roughly from Madhya Mah/Marathwada thru Karnataka towards the Kerala Coast.
In reality, this LWD ( full formed) remains till June, in variable phases, and finally merges with the Monsoon trough (axis)/ITCZ when the ICTZ moves towards the Sub Continent.
3. ENSO: This year also, like last year, we also base our observations on the Multivariate ENSO Index (MEI). An attempt is made to monitor ENSO by basing the Multivariate ENSO Index (MEI) on the six main observed variables over the tropical Pacific.
These six variables are: sea-level pressure (P), zonal (U) and meridional (V) components of the surface wind, sea surface temperature (S), surface air temperature (A), and total cloudiness fraction of the sky (C). (Negative values of the MEI represent the cold ENSO phase, a.k.a.La Niña, while positive MEI values represent the warm ENSO phase (El Niño).The MEI is computed separately for each of twelve sliding bi-monthly seasons (Dec/Jan, Jan/Feb,..., Nov/Dec).
Negative values of the MEI represent the cold ENSO phase, a.k.a.La Niña, while positive MEI values represent the warm ENSO phase (El Niño).
The updated (Mar/Apr) MEI is at -.502 (in Feb/Mar was -0.731), for a slightly decreased ranking.
SOI rises Sharply from =6.0 in February
30 day SOI has risen , and is now at 10.5 ( SOI of -7 to 7 is neutral. Above 7 is La Nina, and below -7 is El Nino ).
The Oceanic Nino Index (ONI) is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. After 5 overlapping seasons showing towards establishment of La Nina, we see a neutral turn. ONI latest is -0.77... ( ONI of -0.5 to 0.5 is neutral. Above 0.5 is El Nino, and below -0.5 is La Nina).
Indicator: heading towards Neutral.
4. The Bay has yet to host a pre monsoon low during April. BB-1 had formed way too early in March.
As discussed, we should normally see a low sometime after the 15th of April. The high pressure region in the Bay, at sea level, no longer prevails.
A strong MJO would hasten the favourable formations and lows, with enhanced precipitation. But the MJO, it seems will remain stalled (without eastward propagation) for the next 10 days .
Hence, not much progress is expected on this front during the next 10 days.
Another factor, which helps the winds gain strength, and bring more moisture into the Indian landmass, is the sea temperatures on both sides of the Peninsula. Optimum (warm) temperatures will hasten and create more clouds, and help in faster forming of the lows from the Bay. Currently , the sea temperatures on both sides of the Peninsula are normal/below normal.
We prefer the Bay parameters to show progress faster , as the SW Monsoon is expected there in 22-25 days…
5. To bring the existing SE winds above the equator (as SW), the ITCZ should move northwards. Around 1st. of May, this should cross the equator. The ITCZ should now come back to its Northward position, as the effective "Lows" created by the Rossby Wave are reducing.
ITCZ is just south of the equator (1 s).
So, overall, we can summarise as:
Parameter: 1) -ve 2) -ve 3) Neutral 4) -ve 5) Normal.
Summary : Three parameters is -ve as of today . Parameters have not improved compared to MW 1 .
We will put up the estimated date of arrival in the MW-3.
But, situations can change fast, and by the time we discuss the next MW, some factors can suddenly become +ve or -ve. So, MW discusses and follows the developments as they emerge, and discuss the parameters as is where is.
No model can commit today when the Monsoon can arrive.
Quantum of rain forecasting in April for June right through September is an impossible task. Things get clearer by last week of April. Vagaries' (in MW) normally remains true to estimates around early May.
Next MW up on 3rd May with Dates of Monsoon Arrival.