The IMD has a strengthening system over the Bay of Bengal in its sights, which means heavy rain will make a comeback in northern Tamil Nadu come Monday. The agency is also forecasting a wet start to the week in several areas, including light rain in Delhi around August 18, and has put out fresh marine warnings for the southwest Bay.
Why the forecast shifted
Meteorologists attribute the change to a feeble trough that lingers along and off the Tamil Nadu coast, where convection remains active. At the same time a new low-pressure area has developed in the northwest Bay of Bengal and the coastal areas nearby. The IMD says it should move to the northwest and pick up strength in the next day or so.
That is an evolving scenario which will no doubt affect the weather in the eastern and southern states, fuelling more activity in Odisha and keeping up the showers and thunderstorms in Tamil Nadu.
Northern Tamil Nadu on alert
A three-day window for heavier spells has been flagged by the Regional Meteorological Centre in Chennai. Their latest numbers show isolated heavy rain in the offing for Chengalpattu, Kanchipuram, Villupuram and Tiruvannamalai between August 17 and 19.
Nilgiris is also likely to be under the influence with heavy rain on the 19th. In Chennai, one can look for light to moderate rain and thunderstorms, with lightning probable in the evening or at night on Sunday.
Thunderstorms and winds
The IMD has put out a caution for parts of Tamil Nadu, Puducherry and Karaikal where lightning and gusts of 40-50 km per hour are in the cards. These are the same wind speeds referenced in the accompanying marine and rain alerts.
Sea conditions and fishermen advisory
Some of the southwest Bay of Bengal will see squally weather with winds in the 40-50 km per hour range. Given how fast the squalls can change and the instability of conditions, fishermen have been told to stay out of the sea for now.
Delhi and the north India outlook
After days of heat and humidity, Delhi is set for some modest relief. The IMD points to widely scattered rainfall across Haryana, Chandigarh and Delhi on 18th August, with isolated heavy falls possible in the region on the 17th and 18th.
Sunday’s figures had the minimum in Delhi at 27.8 degrees Celsius; the mercury is expected to top out at 34 on Monday. Relative humidity was 73 per cent at 8:30 am on Sunday and the AQI was a satisfactory 85 at 9 am.
Odisha remains a key concern
With the Bay system in the process of consolidating, the IMD is warning of extremely heavy rain in parts of Odisha. Catchments are already full in some areas of the state so any new downpours could keep flood risks high and hamper inter-state travel.
Recent rain snapshot in Tamil Nadu
The rain gauges have had plenty to do. Chinnakalar in Coimbatore put in a maximum of nine centimetres, with Marakanam in the Villupuram district not far behind at eight centimetres in the 24 hours to Saturday night. It is a moist backdrop before the new phase of rain sets in.
Key signals to be aware of this week:
– Heavy rain in four TN northern districts, August 17 to August 19
– Nilgiris likely to get heavy rain on August 19
– Gusty winds 40-50 km per hour in Tamil Nadu, Puducherry, Karaikal
– Fishermen are advised to avoid the sea
– Light rain in Delhi around August 18
What comes next
Should the low-pressure area build as we anticipate, the eastern corridors will take the first surge before the plume makes its way to the south peninsula. For the northern belt of Tamil Nadu, the period from Monday to Wednesday is what to watch.
It is well to keep an eye on the IMD and follow local advice, particularly if one is in a storm-prone or coastal zone.
