First heavy rains for Delta to Chennai belt, this monsoon


North East Monsoon (NEM) 2023 had a disappointing October with two cyclone moving away (one to Yemen and one to Bangladesh).  November was left to catch the deficit left behind by October and the first 10 days of November was awesome for Tamil Nadu. However the core monsoon region is yet to get its major spells till date. The core North East Monsoon regions are Delta to Chennai and as we go interior, the rainfall reduces because most of the rains happen due to low pressure in Bay and it has the most impact in the coastal area. This year there was not even single low pressure area near Tamil Nadu.

As a result of that, the coastal areas of Tamil Nadu have got deficit rainfall from 01.10.2023 to 13.11.2023. While South and West Tamil Nadu have got excess rains. Lets see the district wise performance of NEM 2023 till 13.11.2023

North Tamil Nadu districts

Chennai – 190 mm (-61%)
Tiruvallur – 142 mm (-61%)
Chengalpet – 152 mm (-61%)
Ranipet – 99 mm (-58%)
Tiruvannamalai – 121 mm (-54%)
Cuddalore – 175 mm (-52%)
Kallakuruchi – 122 mm (-51%)
Tirupattur – 93 mm (-49%)
Kancheepuram – 174 mm (-48%)
Villupuram – 155 mm (-46%)
Vellore – 137 mm (-40%)

Most of the North Tamil Nadu districts have got -40 to – 61% rains.

Delta & Nearby Districts

Ariyalur – 109 mm (-58%)
Perambalur – 117 mm (-54%)
Mayiladuthurai – 216 mm (-51%)
Thanjavur – 168 mm (-43%)
Tiruvarur – 201 mm (-42%)
Trichy – 143 mm (-35%)
Nagapattinam – 327 mm (-28%)
Karaikkal – 372 mm (-27%)
Pudukottai – 181 mm (-14%)

Most of the Delta & Nearby Districts rainfall have been down by -27 to -58%.

South Tamil Nadu Districts

Kanyakumari – 699 mm (+86%)
Tirunelveli – 385 mm (+39%)
Virudhunagar – 354 mm (+37%)
Theni – 335 mm (+35%)
Madurai – 343 mm (+34%)
Thenkasi – 376 mm (+29%)
Ramanathapuram – 326 mm (+11%)
Sivaganga – 295 mm (+11%)
Thoothukudi – 204 mm (-20%)

Except Thoothukudi, all districts are in positive and Kanyakumari had a dream NEM with very huge excess rains.

West & Interior Tamil Nadu Districts

Coimbatore – 327 mm (+35%)
Erode – 287 mm (+29%)
Tiruppur – 222 mm (+3%)
Namakkal – 193 mm (+1%)
Nilgiris – 296 mm (-13%)
Dindigul – 254 mm (-13%)
Salem – 180 mm (-20%)
Karur – 139 mm (-30%)
Dharmapuri – 156 mm (-31%)
Krishnagiri – 95 mm (-55%)

West Tamil Nadu it was mixed bag for them this monsoon.

What is in Store from Mid-November till first half of December ?

Be it Elnino or +IOD or whatever, the key is MJO and lets see where will be MJO in this period.

We can see that MJO is moved into Phase 1  and by November 20, it will move into the favorable phase 2 and with high amplitude till December 2nd week. There will low pressure after low pressure that can be expected in the next 25-30 days. And when this happens, it is time for Coastal Districts of Nagai to Chennai to rock. Monsoon is going to be very active for the next 25-30 days till end of 2nd week of December.

November 13th Night to November 15th evening

As you can see there are two UAC in a single circulation. On 13-15, the one in SW Bay of Bengal near Tamil Nadu coast is active and gives rainfall to entire coastal districts of Nagai to Chennai and these two circulations merge and the one in Andaman moves up. But who cares, before they merge and move up near odisha, on 13-15th massive convergence is falling over North TN coastal districts and near by districts. Hence, heavy to very heavy rainfall and even in some areas extreme rains are possible on 14 & 15th November.

Can the rains give Dimikki ?

Lets take the 25th percentile 24 hrs rainfall on 14th. We can see that even in the 25th percentile the areas of Nagai to Chennai are in the hotspot in the ensembles. Hence, the probability of heavy rains happening is very very high and less chances of dimikki this time.

Which are the districts needs to be on watch on 14-15

Nagapattinam, Peacockdancesir, Karaikkal, Pondy, Cuddalore, Villupuram coast, Chengalpet, Chennai and Tiruvallur coast are the district to be watched. On 13th night the rains will start in cuddalore-Nagai-Chennai belt and will increase in intensity as we go into 14th November. Chennai will get heavy to very heavy rains on 14 and heavy rains on 15th November. Then the clouds will shift up after the merger of UAC with the Andaman one and move towards Odisha.

Lets see the radar now.

What a beautiful sight in radar with clouds extending 100s kms and these clouds are likely to move into North TN coast as we move into night.

For the public in Nagai to Chennai, keep an vigil on 14 and 15th november, if the rains are too heavy dont move out unless required. Somewhere in these area, there might be a 200 mm event too but we cant tell exactly where it will happen. I will keep you updated the rainfall figure in the FB –, Twitter/X – and the whatsapp channel

Pa Group update – Peacock, Seatown and Nagai districts have announced. Some more districts in North Tamil Nadu would join the list.

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