<p>First off, your observation that Tamil Nadu gets more rainfall in the evening is partially backed by records. <a href="http://onlinelibrary.wiley.com/doi/10.1029/2009JD012644/full#jgrd15857-bib-0003" rel="noreferrer">Sahany, Venugopal, and Nanjundiah, 2010</a> 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:</p>

<p><a href="https://i.sstatic.net/FNn6n.png" rel="noreferrer"><img src="https://i.sstatic.net/FNn6n.png" alt="enter image description here"></a></p>

<p>The Northeast monsoon is different. From <a href="http://onlinelibrary.wiley.com/doi/10.1002/met.1322/full" rel="noreferrer">Rajeevan et al, 2012</a> 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):</p>

<p><a href="https://i.sstatic.net/S02ms.gif" rel="noreferrer"><img src="https://i.sstatic.net/S02ms.gif" alt="enter image description here"></a></p>

<p>Regarding the reasons for this, here are some excerpts from <a href="http://journals.ametsoc.org/doi/full/10.1175/MWR3355.1" rel="noreferrer">Basu, 2007</a>:</p>

<blockquote>
  <p>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</p>
</blockquote>

<p>and </p>

<blockquote>
  <p>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.</p>
</blockquote>

<p>Also worth noting, from <a href="http://onlinelibrary.wiley.com/doi/10.1002/joc.1458/pdf" rel="noreferrer">Roy and Balling, 2007</a>:</p>

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

<p>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.</p>

CC BY-SA 3.0
2016-10-28T13:29:03.033Z
2016-10-28T13:29:03.033Z
kingledion
<p>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.</p>

<blockquote>
  <p>Air is generally cooler at night, and cool air holds less moisture than warm air resulting in rainfall.</p>
</blockquote>

<p>There is a similar Phys.SE question <a href="https://physics.stackexchange.com/q/139164/">here</a> which states the same thing. </p>

<p>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?</p>

<p>Note: I live in Chennai, India. </p>

CC BY-SA 3.0
2016-10-29T02:18:19.327Z
@jamesqpf, unfortunately the reduced moisture "holding" capacity at night won't work for an explanation.  When the air cools to the dewpoint temperature, such that the air is now "full", it will cause fog\dew to form, not rain.  The formation of a significant rain droplet size requires rising air to hold the droplet (and cool the air\release the moisture).  In most places, the maximum rain amount (and likelihood and amount\event) is during the daytime.  There's a good chance Fred is on target with it being connected to geographic effects.
JeopardyTempest
CC BY-SA 3.0
2015-08-06T01:16:54.913Z
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.
Fred
CC BY-SA 3.0
2015-08-06T02:10:21.380Z
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.
naught101
CC BY-SA 3.0
2015-08-06T17:36:20.733Z
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.
jamesqf
CC BY-SA 3.0
2015-08-06T17:38:07.173Z
@jamesqf that's what I said and explained in the link
Madhan
CC BY-SA 3.0
2015-08-06T21:06:42.610Z
@Madhan: But not everyone follows links.  And that answer is more about convection from heating, if I understand it correctly.
jamesqf
<meteorology><precipitation><thermodynamics><coastal><diurnal-cycle>
Why does it rain more at night than during the day?
Madhan
# Why does it rain more at night than during the day?

(Asked by: username_0 on 2015-08-05)

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](https://physics.stackexchange.com/q/139164/) 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.

**Tags:** meteorology, precipitation, thermodynamics, coastal, diurnal-cycle

> **Comments:**
> **username_2**: 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.  
> **username_3**: 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.  
> **username_4**: 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.  
> **username_0**: @username_4 that's what I said and explained in the link  
> **username_4**: @username_0: But not everyone follows links.  And that answer is more about convection from heating, if I understand it correctly.  
> **username_1**: @jamesqpf, unfortunately the reduced moisture "holding" capacity at night won't work for an explanation.  When the air cools to the dewpoint temperature, such that the air is now "full", it will cause fog\dew to form, not rain.  The formation of a significant rain droplet size requires rising air to hold the droplet (and cool the air\release the moisture).  In most places, the maximum rain amount (and likelihood and amount\event) is during the daytime.  There's a good chance username_2 is on target with it being connected to geographic effects.  

---

## 1 answers

### Answer by username_5 on 2016-10-28. Score: 15 | Accepted answer

First off, your observation that Tamil Nadu gets more rainfall in the evening is partially backed by records. [Sahany, Venugopal, and Nanjundiah, 2010](http://onlinelibrary.wiley.com/doi/10.1029/2009JD012644/full#jgrd15857-bib-0003) 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](https://i.sstatic.net/FNn6n.png)](https://i.sstatic.net/FNn6n.png)

The Northeast monsoon is different. From [Rajeevan et al, 2012](http://onlinelibrary.wiley.com/doi/10.1002/met.1322/full) 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](https://i.sstatic.net/S02ms.gif)](https://i.sstatic.net/S02ms.gif)

Regarding the reasons for this, here are some excerpts from [Basu, 2007](http://journals.ametsoc.org/doi/full/10.1175/MWR3355.1):

> 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](http://onlinelibrary.wiley.com/doi/10.1002/joc.1458/pdf):

> 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.


---

