Tamil Nadu braces for Cyclone Nivar, heavy rain alert issued

• Tamil Nadu and Sri Lanka are bracing for a cyclone which is expected to hit its coastal cities on Wednesday. For more than two days, a low-pressure system had prevailed in the south Bay of Bengal.
• On Monday, the Indian Meteorological Department (IMD) said that the system had intensified into a depression and lay 630kms south-southeast of Chennai.
• “It is expected to move northwest and cross Tamil Nadu and Puducherry coasts between Karaikal and Mamallapuram on November 25,” said the IMD’s bulletin issued at 9.30 am on Monday.
• Once strengthened, the cyclone will be named Cyclone Nivar, a name proposed by Iran.
• The weather department has also warned of squally winds over Andhra Pradesh, Tamil Nadu and north-east Sri Lanka as the system approaches the east coast, in the coming few hours.

 

• Tamil Nadu, Puducherry and Karaikal remain on ‘red’ alert with the possibility of heavy to very heavy rainfall forecast on November 25 whereas an ‘orange’ alert prevails for Rayalaseema, Telangana, south interior Karnataka and coastal Andhra Pradesh where heavy rain is forecast during November 24 – 26.
• It will be the second cyclone formed in the Bay of Bengal in 2020 after Super Cyclone Amphan crossed the West Bengal coast in May.

CYCLONE NIVAR

• Cyclone Nivar might make landfall along the Tamil Nadu coast between Karaikal and Mahabalipuram on the afternoon of November 25.-IMD.
• However, any predictions by IMD have to be treated with caution as cyclones in the last few years have been highly unpredictable.

CYCLONE PATH TRAJECTORY

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.
• Throughout August, the Arabian Sea was warmer than usual by two-three degrees Celsius.

• 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.
• Regions of Tamil Nadu have been kept under a “red warning”’—which urges residents and authorities to take action.

• 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.
• La Niña tends to enhance cyclone formation and also higher category ones since during a La Niña they for further down in the tropics and travel longer. 

• 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.
• The wind gusts of up to 120 km / hr making the storm a severe cyclone. 

LANDFALL

• This will be first cyclone to make landfall on the Indian coast in 2020.
• The second to form in the North Indian Ocean region after severe cyclone Gati in the Arabian Sea in 2020.

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

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.
• The outflow in upper steered ridges are always allow the cyclones to breath well .

• 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.

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

Cyclone Nivar may leave devastating effects on north Sri Lanka and south Tamil Nadu coasts.

• 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.
• Fishermen from Tamil Nadu, Pondy and Andhra are not requested to venture into sea from today.
• Strangely the cyclone which try to avoid Sri Lanka and move towards TN coast are all with Coincidence starts with letter “N” – Nisha in 2008, Nilam in 2012 .
• India Meteorological Department made presentation on the present situation and mentioned that the status is being shared with the concerned State Governments.