Thread by @Selwyyyyn

#Monsoon2023 Onset Conditions slowly evolving at the background over S-SE Bay as Lower level wind flow seen getting back to normal after got disturbed last week by #CycloneMocha . Cross Eq Flow/ITCZ associated rains likely over Nicobar Islands from 18th May.

If we observe the above animation closely ,I have drawn a line for understanding the progression of Monsoon as we could see the cross Eq flow slowly establishing &extending NW gradually as days progress. This is how Bay branch monsoon progress into #srilanka (25/26th May)

Zonally oriented East-west shear line in the lower troposphere also seen appearing in the next 4-5 days extending from S.Arb sea into Andaman &Nicobar islands. This is also criterion considered for Monsoon arrival over Bay islands

Of course for kerala onset conditions, we have to wait for Anticyclone to disappear & establishment of somalia jet over Sw Arb sea as they make a strong convergence over SE arb sea adj kerala leading to onset vortex/heavy rains along the coastal areas.

Another thing to highlight in this forecast animation is the domination of Sub tropical westerlies in Bay of Bengal. Usually it descends into Bay from Eastern India to make convergence with Cross eq flow to make an ITCZ convergence/rains over central Bay allowing Eq flow to gain

But in this case, the convergence area is sticking over Andaman latitude & not shifting Northward in the Bay of Bengal ,indicating the Monsoon progression might be sluggish during last week of May. Anyhow need to see the consistency on this

Onset of Monsoon rains over a region would be clear cut & significantly marked in most cases with steady increase in rainfall, changes in the lower level winds& also large scale changes in the atmosphere But in some years we may not see such a typical/textbook onset conditions

"Every year would be different". In some years, be it Kerala or A&N islands onset, large scale monsoon onset days coincides with #MJO convective phase which usually leads to Heavy spell. While in other cases onset would delays & also weak when it coincides with #MJO Suppression

Currently we are under similar ,suppressive conditions but background setup slowly evolving for monsoon onset like conditions over Bay of Bengal. In this kinda cases, rainfall would be subdued, dismal &sluggish. Irrespective of the conditions, I 'd stick with my prev onset dates

Nicobar island around 20th May & #SriLanka around 25/26th May & #Kerala onset by 31st May/1st June. In most of the #Elnino & positive IOD years,monsoon onset was delayed &progression was sluggish. However considering the recent models Ens guidance, hoping it might be on time

Also I would like to say that most of my observation &Analysis would often vary from typical understanding so its highly recommended to follow official agency bulletin/forecast if you are in the place of decision making.

DC : @TropicalTidbits @Weathernerds