Cyclone Nivar : Explained | UPSC

RISE IN SEA SURFACE TEMPERATURE

• Warm ocean waters in the Bay of Bengal, Arabian Sea and the Indian Ocean have been a result of anthropogenic global warming.
• Just this August, low pressure systems, which are the precursor storm systems to cyclones, during the monsoon season caused extremely heavy rainfall along a central belt across the country from Odisha to Gujarat.
• One reason for the heavy rainfall in August was the unusually warm Arabian Sea.

• The normal sea surface temperatures here are about 28-29°C, the temperatures this August reached up to 29-31°C.
• The sea surface temperatures in the Bay of Bengal are also in the range of 29-30°C,-IMD

ALERTS AND WARNING – IMD

• A deep depression in October had also carried much more rainfall than normal, causing extremely heavy rainfall in many parts of Telangana and Andhra Pradesh.

• The coastal areas of Andhra Pradesh and Yanam have also been kept under an “orange alert” —meaning “be prepared”.
• Hyderabad witnessed one of its heaviest showers in the century and floods that brought large portions of the city to a standstill.
• More rainfall than normal is another concern around cyclones in a world of climate change.

IMPACT OF LA NINA

• Another important factor for cyclone formation and behaviour in this season would be the prevalence of the La Niña phenomenon in the equatorial Pacific Ocean.
• On October 29 the WMO declared the prevalence of a moderate to strong La Niña event in the central and eastern equatorial Pacific Ocean.
• The phenomenon will continue till the end of the year and continue into the first quarter of 2021.

• This year has been a bumper year in the Atlantic so the Pacific and Indian Oceans are somewhat calmer.
• The total number of cyclones doesn’t increase that much so a higher number in the Atlantic tends to keep the numbers low in the other oceans.

ABOUT-CYCLONE NIVAR

NAMING OF CYCLONE

• IMD noted the cyclonic storm was christened Cyclone Nivar by Iran.

DEPRESSION

• Nivar currently lies as a depression some 600 km south south east of Puducherry in the Bay of Bengal.

EYE

• It will intensify into a deep depression by the evening of November 23 and a cyclone by the morning of November 24.

WINDSPEED

• The wind speeds at the time of landfall are likely to be in the range of 100-110 kilometres per hour.

LANDFALL

• This will be first cyclone to make landfall on the Indian coast in 2020.

• It might bring heavy rainfall to the southern states of Tamil Nadu, Andhra Pradesh, Karnataka and Telangana from November 24-26.

Sources : IMD | Cyclone Nivar : Explained | UPSC

WHY CYCLONE IS STEERING TO NORTH TAMIL NADU?

• As you can see majority of our Cyclone will be steered by the Pacific ridge with upper steering(refer image below)
• Very rarely they take Arabian Sea ridge (Gaja in 2018) in under steering.

• While under-steered systems are choked and does not intensify a lot (Gaja was an exception due to nil wind shear).
• Cyclone Nivar is an upper steered system through the ridge extending from Pacific side.

SOURCES : thetamilweatherman.com

FAVORABLE PARAMETERS FOR CYCLONE TO INTENSIFY

POSITIVES

1. Wind Shear – Ideal wind shear of 10-15 knots and shows decreasing trend.
2. No dry air intrusion.
3. Sea Surface Temp is warming up and ideal

NEGATIVES

1. It is very close to coast – Time is short
2. Very fast movement

IMPACT

• Visakhapatnam and East Godavari districts are also likely to receive light to moderate rains.
• Widespread heavy rains from Delta to Chennai and extreme rains to Delta are expected.