On Thursday Late night and and early Friday 13th morning, the regions around Chennai received unexpected very heavy rains. Amounts of upto 47 cms was recorded, and many a usually drier lakes received a bounty, and filled up the water reserves.
The reason for this, according to me, was due to the "divergence" in the 200 jet streams, almost over the affected areas.
Where divergence (evacuation of mass) occurs in the upper levels, rising motion result. Convergence and divergence in a jet streak is caused by an imbalance of forces as a parcel accelerates into a jet streak then decelerates out of the jet streak.
This could have created a Lower level small Vortex.
The early morning jet stream divergence chart is shown below.
One must remember, that in order to follow any change, or upcoming change in weather, or even a seasonal change, the jet streams must be checked upon. These (Jet Streams) I call the "kings" and are responsible for most of the weather happenings in the lower atmospheres.
Rainfall in mms as on 13th Morning: (Compiled by Pradeep)
Vembakkam (Near Kancheepuram) - 473, Kancheepuram - 342, Puzhal Agro - 227
Puzhal - 211, Redhills Lake - 210, Sriperumbudur Agro - 184, Nemili (Arakonnam) - 178
Madhavaram - 164, Tiruvallur - 163' Avadi - 162, Nungambakkam - 150, Cholavaram Lake - 147, Palavedu (Avadi) - 145, Minjur - 144, DGP Marina - 140
Anna University - 131, Tamaraipakkam - 130, Poonamalle Agro - 127, Thiruvalangadu - 120, Meenambakkam - 118 , Korattur Anaicut (Poonamalle) - 118
Chengalpattu - 100, Tharamani - 98, Katupakkam - 97, Ennore - 95.