Skymet weather

How Cyclone Roanu governed Indian weather before the onset of Monsoon 2016

May 28, 2016 11:59 AM |

Cyclone RoanuCyclone Roanu was the first tropical storm of the season to develop in Bay of Bengal. The system had immense strength, right from the day of its formation, giving exceptionally torrential rains all along the Indian East Coast.

The system as a well-marked low pressure gave record-breaking rains over Tamil Nadu including Chennai initially. Subsequently intensifying into a deep depression, it further battered Andhra Pradesh coast even more gravely. Thereafter, it finally strengthened into Cyclone Roanu and continued lashing Odisha and West Bengal coast and lastly concluded by making landfall over Bangladesh on May 21.

Cyclone Roanu was not limited to giving rains only, in fact, it had much more impact on the Indian weather one could think of. One of such is the onset of Southwest Monsoon over Andaman and Nicobar Islands on May 18.

Moreover, such strong systems bring in some sustain changes even after their passage.

Impact of Cyclone Roanu on Indian weather

Disappearance of wind discontinuity: Peninsular India witnesses lots of weather activities in terms of rain and thundershowers on account of wind discontinuity. This weather phenomenon is a semi-permanent feature that we see during the pre-Monsoon season.

According to Skymet Weather, cyclonic storms tend to govern wind patterns across vast areas. Hence, whenever such systems come into existence, it leads to disappearing of the wind discontinuity.

Now, this feature is not likely to comeback as Southwest Monsoon is on the verge of arriving over Indian mainland. Hence, the present rains over Peninsular India can be attributed to the changeover period from pre-Monsoon season to Monsoon season.

Departure of anti-cyclonic circulation in Bay of Bengal: All this while, the persistent anti-cyclonic circulation in Bay of Bengal kept infusing moist winds along the East Coast.

Again with the passage of the tropical storm, the anti-cyclonic circulation has disappeared. With this, most of the coastal stations are now witnessing winds blowing from land, leading to significant increase in day temperatures. For instance, Coastal Andhra Pradesh has been witnessing extremely high day temperatures resulting in severe heatwave conditions.

Early appearance of east-west trough along Indo Gangetic plains: After hitting Bangladesh coast, the cyclonic storm moved towards Northeast India. This led to change in wind pattern and gave rise to the east-west trough running along the Indo Gangetic plains. This trough has been persistent over the respective region ever since the passage of Roanu.

According to Skymet Weather, we usually witness this trough around the onset of Southwest Monsoon over these areas but this time it has appeared quite early.

Moreover, a cyclonic circulation has also been prevailing over Gangetic West Bengal for several days now. This system keeps getting marked or weaken from time to time.

With both the weather systems, East India has witnessed significant rise in the rainfall activity that includes parts of West Bengal and Bihar.

Increase in rainfall: It was one of the driest April this season and May too began on the similar note. However, formation of the system in the Bay of Bengal around May 12 changed it all.

Coastal states along the East Coast saw heavy to extremely heavy rains thereafter. Most of the stations in Tamil Nadu, Andhra Pradesh, Odisha and even some parts of West Bengal surpassed their monthly average in a day or two only.

Not only this, it had also given some very good showers over northeastern states. This transformed May into the rainiest month of the pre-Monsoon season in 2016.

Roanu has also strengthened the Monsoon current, especially over the Bay Islands. As a result, Port Blair has been witnessing good rains consecutively since the passage of the cyclonic storm on May 16.

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