Vanakkam! Overnight thunderstorms lashed parts of Chennai and left some moisture hanging in the air (relative humidity) — to a maximum of 100 per cent at 5.30 am, according to the Chennai Met Office of the India Meteorological Department (IMD).

The temperature and dew point read at 26.8 degrees C each at that point. Three hours later, the temperature had gone up to 31.2 degrees C while the dew point had dipped to 28.1 deg C, and along with that, humidity to 85 per cent.

Relative humidity

The relative humidity is 100 per cent when the dew point and the temperature are the same. The air is saturated with moisture, and conducive for precipitation, but subject to other conditions.

The dew point is the point below which water droplets begin to condense and dew can form. If the temperature drops any further, condensation will result, and liquid water will begin to form. That’s why we call it relative humidity, because the humidity is relative to the air temperature.

Chennai, though, saw the temperature go up instead from Tuesday morning; so, chances of immediate precipitation are less.

Rain outlook

The wind direction has changed from north-easterly to easterly earlier in the morning to easterly-to-south-easterly, but retains more or less the capacity to rain, judging from the moisture feed from the seas.

The Chennai Met Office forecast is for light to moderate rain at most places over South Tamil Nadu, and at many places over North Tamil Nadu (Chennai included) and Puducherry for the rest of today (Tuesday).

As for Chennai city, the sky condition is likely to be generally cloudy. Light to moderate rain/ thundershowers may occur in some areas. Maximum and minimum temperatures may range between 32- and 26 deg Celsius.

What the private forecasters say

Private forecaster Skymet Weather, however, does not find much scope for rain anytime during the day with the humidity levels staying in the range of 70 per cent or just above.


US-based international forecaster AccuWeather has predicted a mostly cloudy day with a thunderstorm or two.


International forecaster Meteologix, too, hints at the possibility of light showers or thunderstorms for the city and neighbourhood during the day, while it gets heavier to the South.


The RainViewer Storm Tracker showed thunderstorm bands racing to the West and South-West after dropping overnight rain over parts of the city. Smaller bands were waiting to strike the southern parts of the city.


As always, the city's own blogger @ChennaiRains put the overnight developments and the outlook for the day succinctly in a morning tweet.



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