Weatherman Special – Cyclone Nivar will cross between Pondy & Chennai on 25th Night to 26th morning


Note: Athigara porvamana vanilai arikkaiku, neengal official agenyin, forecast ai nadavum. Post podran podran solli, i have made you wait and i should not put a mokka post, so a big post. This post is pure interpretation with personal capacity. To be honest, this has been one of the difficult cyclone to interpret even with all the high end numerical models available.  From bottom of my heart i want to appreciate IMD officials for sticking with their track of close to south of Pondy.  Will try to answer most of the common man question in this post. If there are grammatical mistakes, please ignore, compiled in half sleep.

1. Where is the cyclone now and what intensity it is in ?

We can see here that the Cyclone is still over 300 kms away from our coast line (as of mid night on 24th) and is parallel to delta coast above north east of Sri Lanka. It has just moved above 10 N latitude moving in W-NW direction. The intensity is around 50 knots and pressure is 991 mb with wind speeds of already close to 100 km/hr.

2. Cyclone Nivar is expected to cross which are in Tamil Nadu and Why?

There is still no consensus among the models in the crossing area. But ippadiya wait panna, then i have to put post only after the cyclone crosses the land. The Europeans ECMWF, British UKMET and German ICON are more favorable for Nivar to cross towards Pondy to Chennai coast somewhere close to Mahabs. While the North Americans USA GFS and Canadian GEM are making the landfall close to Karaikkal / Parangipettai belt. Nammathaan USA ethu sonnalum keppom la, so IMD GFS model also takes it to Delta.  Such a large divergence seen among the models with just 24 hours to go in to landfall and lot of katchi thavalas till today evening.

My interpretation of the above, the steering ridge from the pacific still controls the movement of the Cyclone with firm grip and until this Pacific Ridge steers the cyclone can take only W-NW path if it becomes strong. If it is a weak cyclone it can be pushed directly to Delta from east with pure west movement. And even in strong cyclones for it to move pure west, it has to be steered by Arabian Ridge which is very far away. The cyclone has already crossed 10 N latitude (please refer the 1st image above), there is very little chance for it to move pure west and crash into Delta like the American says and the Teacher from Delta says.  So those who are in Delta, there will be some rains but Cyclone Nivar is not for Delta.

What is steering in simple layman i will try to explain this – Cyclones are pallam (low) and High pressure are medu when ur inside u can traverse only around the ridges of the medu (high pressure). That is steering. No apply ur mind on the above image and you can understand why Nivar is moving – W-NW.  There are many other complex factors too. But will stop with this.  Further, the Ensemble members of ECMWF also favors a track of crossing Pondy to Chennai around Mahabs (+ or – some kms).

So the conclusion is that Cyclone Nivar is expected to cross between Pondy and Chennai near Mahabs-Kalpakkam areas with some + or – some kms on the night of 25th to morning of 26th. The difference is not much between Mahabs and Chennai, if some little deviations occur, there are slight chances that cyclone might even land over Chennai.

4. Will Cyclone Nivar become stronger than Gaje Cyclone ?

Wind Shear of 5-10 knots and it is ideal for the Cyclone to intensity. We have seen in the past a wind shear 40 knots will destroy a strong cyclone into a skeleton within few hours. This low shear for Nivar path ahead with further decreasing trend will make one of the ideal conditions for intensification.

Next let come to the outflow. In simple terms, at lower levels (1-4 kms height) the inflow winds will come (converge) into the Cyclone, thes winds coming inside cant be trapped inside the cyclone itself, the winds coming at lower levels will have to escape out (diverge) at higher (10-12 kms height) levels. Let make it simple its nothing but breathing, we inhale and exhale to keep our-self alive. Like that Cyclone inhale (inflow) and exhale (outflow) to keep them alive. If outflow is not good what happens, winds keep on coming and at one point they collapse.

Those these are not the only parameters but these two as of not outweigh all others, with MJO in basin, optimal TCHP, good SST of 28-29 C and no dry air intrusion, i cant see any negative reason to weaken this Cyclone Nivar. High chances that this will become stronger than Gaje Cyclone.

5. What will be sustained wind speeds and gusts

We follow 3 min average for sustained winds and gusts (small burst of winds at times). With nothing negative to stop this cyclone we can expect this cyclone to intensify on par with Thane Cyclone (140 km/hr) or even better. The northern side of the cyclone crossing areas will get good winds too the ECR belt can expect 100 km/hr winds. So 26th morning will be a gusty morning for us.

140 km/hr – Pondy – Marakannam- Mahbas coasts (mid-night to morning of 26th)
100 km/hr – Cuddalore coast (midnight of 25th)
100 km/hr – Chennai Coast (26th morning)
100 km/hr – Chengalpet and Kancheepuram (26th morning)
80-90 km/hr – Ranipet, vellore and Tiruvallur (26th Noon)

6. What will be Rainfall and what are the districts ?

For accumulated rainfall till 26th evening,

Extreme Rainfall might happen around Cuddalore, Pondy, Villupuram and Chengalpet areas.

Very heavy rains might happen in  – Chennai, Kancheepuram, Tiruvallur, Ranipet, Kallakuruchi, Tiruvannamalai and Vellore.

The interiors will get on 26th November while the coastal areas will get on 25-26th November. We will never know which spot among these districts where a big event might occur, which is always associated with Cyclones.

The rains will be intermittent to start with once we are close to the centre, we might see non stop rains for few hours when the centre passes the areas in above districts.

7.  waves

The areas north of crossing will have the waves very rough. So right from Cuddalore to Nellore Coast dont venture out into seas or even go near the sea shore while crossing. The storm surges might come and wash you away.

Namma post na stats illama irukkathu, lets see the past cyclones in Tamil Nadu and wind speeds in Chennai and we will know where Nivar will stand.

9. Why Chennai (KTCC region rocked today) while others places did not even get rains

The concave coast is one major reason and the location of Chennai and spin of bands resulted in clouds right over KTCC. And our Chella Kutty Radar is back working overtime. Tomorrow the rains will be intermittent and as we near the landfall time, few hours before that we will get good non-stop rains when the centre is close to us.

KTCC (Chennai & 100 kms) Rainfall on 24.11.2020

in mm

Tambaram – 90
KK Nagar – 83
Nungambakkam – 77
Meenambakkam – 70
Alandur – 70
Kelambakkam – 58
Kolapakkam – 55
Ayanavaram – 52
Chennai Collectorate – 51
Perambur – 40
Hindustan University (Kelambakkam) – 39
West Tambaram – 37
Taramani – 35
Chengalpet – 35
Tondiarpet -34
Poonamalle – 30
Redhills – 28
Anna University – 28
Ambattur – 26
Puzhal – 24
Korattur Anaicut – 24
Uthiramerur – 24
DGP office – 23
Ennore – 19
Chembarabakkam – 19
Madurantagam – 18
Tiruporur – 13
Sruperumbedur – 13
Tiruvallur – 11
Gumdidpoondi – 10

Rainfall in KTCC (Chennai and surrounding) till 2.30 am on 25.11.2020 (ongoing)

in mm

Nungambakkam – 131
Guindy – 114
Meenambakkam – 94
Somangalam (West Tambaram) – 75
Taramani – 92
Puzhal – 73
Ennore – 65
Chembarabakkam – 61
Kolapakkam – 60

Expecting Nunga to touch 200 mm by morning 8.30 am.

11. Maximum sustained winds (3 min average) for Tamil Nadu cyclones in last 30 years

(Min 100 Km/hr at crossing)

1993 – Karaikkal Cyclone – Karaikkal – 167 km/hr
2011 – Cyclone Thane – Cuddalore – 140 km/hr
2018 – Cyclone Gaja – Vedaranyam – 130 km/hr
2000 – Cuddalore Cyclone – Cuddalore – 120 km/hr
1991 – Karaikkal Cyclone – Karaikkal – 120 km/hr
1992 – November Cyclone – Thoothukudi – 120 km/hr
2016 – Cyclone Vardah – Chennai- 122 km/hr
1994 – Madras Cyclone – Tambaram – 116 km/hr
1996 – December Cyclone – Chennai- 100 km/hr

12. Highest Recorded sustained wind speeds (3 min average) in Chennai in last 25 years

(Min 60 Km/hr at crossing)

Cyclone Vardah (2016) – Meenambakkam – 122 km/hr, Nungambakkam – 114 km/hr and Ennore – 89 km/hr
1994 Madras Cyclone – Tambaram – 116 km/hr, Nungambakkam – 90 km/hr, Meenambakkam – 74 km/hr
1996 December Cyclone – Nungambakkam – 100 km/hr
Cyclone Nilam (2012) – Nungambakkam – 74 km/hr and Pondy – 62 km/hr
2001 Nellore Cyclone – Nellore – 65 km/hr
Cyclone Jal (2010) – Ennore – 61 km/hr

13. Strongest cyclones in terms of pressure to cross Tamil Nadu / SL in last 40 years during NEM

(Min 975 mb pressure at any point of life time)

1978 SriLanka Cyclone – 953 mb
2000 Cuddalore Cyclone – 959 mb
1996 Chennai Cyclone – 967 mb
1993 Karaikkal Cyclone – 968 mb
2011 Cyclone Thane – 969 mb
2000 SriLanka cyclone was 970 mb
1984 Cuddalore Cyclone was 973 mb
2018 Cyclone Gaja – 975 mb
2016 Cyclone Vardah – 975 mb
1984 Sriharikota Cyclone was 975 mb

14. Highest 24hrs rainfall in Tamil Nadu from Cyclones in North East Monsoon in last 10 years

Cyclone Phyan – 820 mm in Ketti, Nilgiris in November 2009
Cyclone Nisha – 656 mm in Orathanadu, Thanjavur in November 2008
Cyclone Ockhi – 451 mm in Papanasam Dam, Tirunelveli in
Cyclone Vardah – 382 mm in Shollinganallur, Chennai in December 2016
Cyclone Nilam – 240 mm in Yercaud, Salem in November 2012
Cyclone Gaja – 197 mm in Kodaikanal, Dindigul in November 2018
Cyclone Thane – 180 mm in Kallakuruchi, Villupuram in December 2011
Cyclone Jal – 160 mm in Gingee, Villupuram in November 2010

15. Do and Dont’s during Cyclones for Public.

After Nivar avaroda brother follow panni varar. ‘Tamil Nadu cant rest so soon, it needs to be vigilant.

Good morning to all. Intha post padikkama, next post epponu ketta semma gaandu ayuduvan !!!  Will put up next post if there is some change in the above. Will switch off the phones and enjoy the rains.

Share and Enjoy !

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