Wednesday, May 09, 2012


Vagaries' sub-continent Forecast for Thursday,10th thru Saturday,12th on Current weather Page. 


Mumbai/Pune forecast and Mumbai Lakes Position on Mumbai Page:



Scotland:-No sking in March, But full force in June :..For related articles, See International Page and Mark's Blog.
See Inter Active Page updated with a sensational Pic from HP



Monsoon Watch 5-Arrival Dates.


As always explained, the MW parameters are to represent the progress of the developments in the Monsoon build up. On "as-is-where-is-today" basis, Vagaries calculates and forecasts the arrival date of the Monsoon. Again, these parameters are not referred in this MW for the quantum of rainfall. 


Bay factor
In the Bay sector, the cross-equatorial wind is building up across the East Indian Ocean. Strong South-West winds have suddenly developed in the South Andaman Sea, and SW winds are now required to clock 30 knts South and SW of Sri Lanka. Gauging from the the wind speed, we can expect the Monsoon to strike the South Andamans Seas by 15th of May, and the Middle Andamans by the 18th. (Almost on schedule). 


As stated, the first South-West Monsoon rains normally hit the South Andaman Sea on 12th.May. And proceed to the Middle Andamans by the 15th. By the 20th. it normally covers the Islands totally.


This year we should see a feeble Monsoon current in the South Seas by the 15th.
Onward Monsoon progress Northwards towards the NE States will have to be monitored.


The latest winds in the Bay continues to show strong winds rushing Northwards along the East coast of India, and re-curving into a Westerly flow of winds at the South Myanmar coast.






A lone pre-Monsoon low (B-1) had appeared in the region (end April) this year. SST in the Bay is now very conducive to host a low soon, in the South Andaman Seas.(See SST Map). 
Indicator : +ve


The cross equatorial Wind flow: This flow off the East African Coast, in the Western Indian Ocean, this was a bit "disrupted" previously, but has now re-formed itself fast, and is strong off the East African Coast South of the Equator. The Somali Current, is getting defined, and blowing strong! 
We will wait for the Somali coastal SST to drop further (should ideally be 18-20c). In the map, observe the difference in SST along Somali Coast and Central Arabian Sea.
The previously weak factor, the equatorial cross flow South of the Arabian Sea, is steady. 


The Mascarene highs are established at 1030 mb, are are now "pushing" the South-Easterlies from below the Equator.  


However, I feel, a good booster required for the Arabian Sea branch of the Monsoon, is still wanting, and is at least a week away. 
Indicator: Improved since MW4


Seasonal Low: With the heat factor still lacking absolute "full strength", in the Northern regions, the Seasonal Low core in the Thar Desert is now somewhat "unsteady", with a core pressure at 1002 mb, and requires to spread more westwards, rather than east. This (pulling Eastwards) is happening due to M1. 


The heat waves are still missing, with the minimums still showing vast regions in the below normal range. By this time each year, vagaries normally charts the "above 30c" minimums. But this year as yet, forget 30s, we are still barely reaching 25s in the night, with the odd one out in the NW plummeting to below 20c.
And the days ? 45c is just about getting its foothold!


To refresh, reproducing a clipping from Vagaries of 10th May 2011: "Readings of 10th May:
Hottest in Asia: Larkana (Pakistan) 48c, Nawabshah and Jacobabad  47c.
Hottest in India: 45.2c at Khajuraho, Agra  44.7c,  44.5c at Brahmapuri. 
Lows above 30c in India: Khajuraho 31c, Gwalior  30.7c, Gondia  30.4c, Kota  30.3c, Satna  30.2c. No lows above 30c noticed in Pakistan".


I only hope the below par heating and seasonal low formation in the North do not play spoilsport.


A North-South trough indicates the line of wind dis-continuity is unfavourably tilted towards the east in the Peninsula region. Normally, a perpendicular N-S trough is an ideal pre monsoon formation, and is a fore-runner for the seasonal low to stretch its presence over central India.(See Thai Met Dept Map). 






As mentioned in my MW prevoiusly, the creation of a good gradiant between Kerala pressure and Rajasthan/Sindh pressure is an absolute requirment. And that is a must for creating a pull Northwards for the Monsoon. Overall position in this parameter is improved slightly since MW 4. 
Indicator: Neutral


The ITCZ now runs along the Equator from the African coast to Sumatra Island. Normal, for it to touch the equator around the 10th. (For more read previous MW).
Indicator: +ve


The 200 hpa jet stream: 






Normally, they should be Easterlies right upto 20N by May end. This would facilitate the Northward movement of the Monsoon Current. 
Today, the Easterly jet stream is developed upto 5N.
These 200 hpa jets winds need to come upto 8N by 15th.of May at least, and then move upto 10N before 20th.May, to be in time for the Andaman Sea Monsoon arrival. But forecasting maps are slow to show this, and indicate a slow movement Northwards. 
The jet streams are far too Northwards, and are dipping South in a loop today.
Indicator: Slow, hence -ve.




Arrival Time Conclusion: 
Considering all the other parameters, with the aid of a low, (pulse from the Pacific), SWM could advance into the South and Central Bay Islands around the 15th of May. Should cover the Andaman Islands by the 20th of May. Further advance will depend on the strength of the low.


Arabian Sea branch will see the SWM advance into the Maldives region by the 22nd of May. 
Sri Lanka should get the Monsoon on its shores by the 26th. 
However, a brief halt there might result in the SWM advancing into Kerala around 3rd/4th June.


(This Monsoon chase is my personal view, and my personal analysis and deciphering is done as per my assumptions. Should not be used for commercial purposes). 


Next MW-6 will be published on 20th May evening.


Current Weather conditions and city wise forecast for the next 3 days will be published today (Wednesday) evening by 11.30 pm on Current Weather Page.
Also Mumbai Special with Lakes Position.

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