Moderate El Nino during NEM – A welcome sign

It is expected a moderate El Nino is on the cards along with possible Negative IOD during the NEM season for us.  This could be a blessing in disguise for us as El Nino could possibly act as counter measure in terms of cyclogenesis of severe and very severe cyclones.

During El Nino years, the wind flow at lower levels are predominantly easterlies with strong westerlies aloft. This situation generates a vertical wind shear in this region, which is the inhibitive factor for cyclone genesis, hence strong easterly waves are associated with excessive rainfall over the region.

Additionally if one goes by research undertaken by De & Mukhopadhyay (1999) “The frequency of cyclonic systems formed is lower during the ENSO years compared to that during Anti ENSO years. However, during ENSO years these cyclonic systems follow a more westerly path and cross Tamilnadu and the south Andhra coast, thus giving enhanced precipitation. During Anti ENSO years, these cyclonic systems move in a more northerly direction and often recurve and hit either West Bengal or the Bangladesh coast. During ENSO years, the mean ridge line at 200 hPa level in the NE monsoon is around 13N, while it is situated at 16N during Anti ENSO years.”

http://onlinelibrary.wiley.com/doi/10.1017/S1350482704001306/pdf

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