Southwest Monsoon continues to stutter its way across Peninsular India

Weather Update
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Since the onset of Southwest Monsoon over Kerala it has been stuttering and stammering its way through Peninsular India. Though it arrived a couple of days before time the rainfall performance has been poor over the west coast state. As of 8th June the seasonal rainfall, since 1st June, stands at -32% overall. Thrissur, Kottayam and Malappuram dts are the only districts that have received normal rains with rest all Deficient or worse. Even among these three districts Thrissur is the only district with a positive anomaly. This pretty much sums up the performance of Southwest Monsoon so far over southern parts of Peninsular India.

In a way this early season stutters for Southwest Monsoon was not completely unexpected. The delayed arrival of Summer over Central and North India meant thermal gradient was always playing a catch up game. A couple of months back seasonal weather models were estimating Southwest Monsoon to start with a flourish. This forecast of early season flourish was possibly on the back of a flip to La Nina from El Nino. The latest seasonal outlooks though indicate sub par rainfall during the month of June over most of India. Question though remains whether poor start to monsoon in Kerala is a smaller issue or a larger problem of shifting monsoon dynamics. As this post a year back indicate Kerala is facing a weakening of monsoon dynamics during the first half.

Southwest Monsoon has started to knock the doors over the northern parts of Peninsular India. The last couple of days have seen Monsoon check in not only over Maharashtra but also Chhattisgarh and Odisha too. IMD expects Monsoon to cover most of Maharashtra including Mumbai over the next 48 hours. The East west Shear Zone currently seen over the northern parts of Peninsular India has pushed the onset up to here. Weather models indicate over the next few days this is likely to remain near stationery leading to a potential stall of further progress.

Initially the cyclonic circulation was expected to move up along the Konkan coast dragging monsoon onset along with it. Now all the models expect the cyclonic circulation to drift East across Peninsular India. This could be due to the strengthening Westerlies at lower levels pushing across the circulation along the East West Shear Zone. Under normal circumstances if this circulation descends into an LPA it would have given a great impetus to the monsoon. But sub seasonal models remain bearish for a Monsoon low forming over the next couple of weeks.

One of the reasons for the poor start to Monsoon could be the unfavourable movement of BSISO. IMD prefers to call this intra seasonal oscillation as MISO. Models indicate BSISO to remain skewed towards South China Sea and West Pacific over the next couple of weeks. MJO has been struggling against the flipping base state of Pacific from Warm to cool regime since summer. It could continue to struggle until mid July when the base state shifts to the cool regime. Once the base state starts hastening towards La Nina things will see a huge improvement. We could then possibly see MJO and associated BSISO work wonders for Southwest Monsoon. A word of caution though seasonal outlooks from JAMSTEC indicate a high chance of La Nina Modoki this year. This could potentially mean Southwest Monsoon may not be a straight forward La Nina / Positive Rainfall equation.

In the meanwhile this quasi stationery onset of Southwest Monsoon may bring about enhanced thunderstorm activity over some parts of Peninsular India. In particular North Karnataka, AP & TS states may see heavy rains over the next few days. Potentially we may see localized flooding in some of the cities like Hyderabad in the next couple of days. Additionally the wind convergence triggered by the East moving circulation could open up another window of opportunity for North TN. This window may open up later next week, but more on that as things evolve. Until then we may have to be satisfied with cooler than normal day time temperatures and scattered thunderstorm activity over Tamil Nadu.