Monsoon Watch 5- Part 1( Arrival Time).
As always explained, the MW parameters are showing the progress of the developments in the Monsoon build up. On as - is - where - is basis. Vagaries calculates and forecasts the arrival date of the Monsoon. These parameters are not for the quantum of rainfall.
Vagaries will now, for the 1st time, attempt at forecasting the quantum of Monsoon rainfall. This is in the Part 2.
Bay factor: In the Bay sector, the cross-equatorial wind is building up across the East Indian Ocean with clouds massing west of the Bay Islands. Strong South-West winds have suddenly developed in the South Andaman Sea, and SW winds are now clocking 30 knts south and SE of Sri Lanka. Gauging from the the wind speed, we can expect the Monsoon to strike the South Andamans Seas by 13th, 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 covers the Islands totally.
As the South-West winds have geared up, and the moisture inflow has picked up in the region,since the last 2 days, by the 10th, we should see a feeble Monsoon current in the South Seas.
Onward Monsoon progress Northwards, will have to be monitored.
In this sequence, we now have a weak low. A weak low has formed in the South West Bay on the 5th. viz.96B. I would not consider this low as a pre-monsoon "bay" low, but just an embeddment in the MJO.
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 has appeared in the region (end April) this year. SST in the Bay is now very conducive to host a low anytime, but in the South Andaman Seas.(See SST Map). Indicator: +ve
The cross equatorial flow, off the African Coast, in the Western Indian Ocean, a bit "disrupted" previously, has now re-formed itself fast, and is strong off the 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. (See SST map).
The previously weak factor,the equatorial cross flow South of the Arabian Sea, is getting stronger.
The Mascarene highs are established, 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 1000 mb, and requires to spread more westwards, rather than east. This (pulling Eastwards) is happening due to the W.D. M1.
A North-South trough indicates the line of wind dis-continuity is getting favourably tilted towards the east in the Peninsula region. Normally, a perpendicular N-S trough is a 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 since MW 4. Indicator: +ve
Arrival Time Conclusion:
SWM could reach the South Andaman Sea Islands, the Southern most tip, by 13th May. Progress into the Middle Andamans will be within 2 days, and should cover the entire
Considering all the other parameters, on today's situation, SWM should hit Kerala a few days behind scheduled date, by the 3/4 th June. Northwards into coastal Karnataka should be smooth (nothing adverse) and arrive there by 5/7 th June.
Monsoon Watch - 5 Part -2 will be published on tomorrow (Friday) nite.