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I'm living near a sea, and it rains mostly and heavily at night from 11 PM to 3 AM. The weather is mostly clear during daytime.

Air is generally cooler at night, and cool air holds less moisture than warm air resulting in rainfall.

There is a similar Phys.SE question here which states the same thing.

Is this the only reason why it rains most at night, or are there any other factors which may affect the reason for raining more at night?

Note: I live in Chennai, India.

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    $\begingroup$ It could be because of where you live - latitude & topographical features etc. I've lived in a number of coastal locations spread over a large range of latitude & rainfall has been spread out throughout the day, its never been concentrated between 11pm & 3 am as it is were you are. $\endgroup$
    – Fred
    Aug 6, 2015 at 1:16
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    $\begingroup$ It might be useful to add your approximate location (which side of which sea?). Then people might be able to relate the answer to global patterns + orography (e.g. if the trade winds are on-shore, that might cause night-time uplift, which would cause precipitation. $\endgroup$
    – naught101
    Aug 6, 2015 at 2:10
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    $\begingroup$ @naugh101 - usually in his case( I live in a nearby latitude/longitude) thunderstorms occur at night during the summer monsoon and occur at night and day during the autumn monsoon $\endgroup$
    – user1066
    Aug 6, 2015 at 5:06
  • $\begingroup$ @naught101 - for the summer monsoon he lives in a rain shadow area so he is dependent on heat and other factors during the day. Sometimes thunderstorms start as early as 4 pm in his area. $\endgroup$
    – user1066
    Aug 6, 2015 at 5:07
  • $\begingroup$ Perhaps BECAUSE cool air holds less moisture? The air heats up during the day, and collects as much moisture as it can hold at that temperature. At night it cools down and can no longer hold the moisture, so it rains out. $\endgroup$
    – jamesqf
    Aug 6, 2015 at 17:36

1 Answer 1

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First off, your observation that Tamil Nadu gets more rainfall in the evening is partially backed by records. Sahany, Venugopal, and Nanjundiah, 2010 provide data on diurnal scale rainfall distribution during the Southwest monsoon season shows that Tamil Nadu is dry from 0530-1430 each day, and likely to be wet from 1730-0230:

enter image description here

The Northeast monsoon is different. From Rajeevan et al, 2012 the NEMR (North East Monsoon Rainfall) peaks in the evening for most of Tamil Nadu but the coast facing the Bay of Bengal (including Chennai) peaks in early morning (0330-0630):

enter image description here

Regarding the reasons for this, here are some excerpts from Basu, 2007:

In the Tropics most of the rainfall is from the tall clouds (Cu or Cb) formed by convection within a deep layer of the atmosphere. The usual forcing for such clouds to form is the heating from below by the solar radiation absorbed by the ground during the day. This forcing is maximum near the time of maximum surface temperature and the first of the thunderstorms caused by insolation start near 1430 local time

and

Over the sea areas along the east coast (south of 15°N) too, the maximum in precipitation occurs in the early morning hours as the synoptic-scale westerly is weak over this region and the diurnal variation is dominated by the land–sea breeze.

Also worth noting, from Roy and Balling, 2007:

The strength of the diurnal cycle is greatest in the peninsular region with close to 96% variance explained for stations located in Tamil Nadu.

My interpretation of this is that inland Tamil Nadu sees high surface temperatures from sunlight through clear skies striking the ground. The resulting heat is released in the late afternoon and evening, which causes cumulus or cumulonimbus cloud formation and rainfall. During this, the ground cools off at a rate faster than the nearby Bay of Bengal. This causes oncoming sea breezes laden with moisture and coastal rainfall peaks in the early morning hours. In Tamil Nadu especially, this pattern is very stable.

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    $\begingroup$ this is a very good answer and thorough. Very well written and easily understood. I compliment you ! Happily upvoted. $\endgroup$
    – user1066
    Oct 29, 2016 at 15:40

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