More cyclones hit the East Coast of India

Just by reading the newspapers over the years, one can recall more cyclones hitting the East Coast of India than hitting the West Coast.
I thought that I would check online if somebody else has observed, and explained, this observation.

I found one post which I reproduce below, from an IAS (aspirants/trainees?) discussion forum:

http://discuss.forumias.com/discussion/595/gs-geography-questions


“Why do cyclones strike at the Eastern coast in India and not much in the Western coast. As if we notice it is seen that cyclones typically create much havoc in the Eastern coast rather the Western coast?
The main cause is Coriolis effect.
Since India is in Northern Hemisphere, so in here, due to Coriolis force, winds tend to turn toward their right while moving.
So, whatever cyclones are formed in Bay of Bengal, they turn toward their right, hitting our Eastern coast.When cyclones are formed in Arabian sea, they get deflected away from india.
But, they are exceptions also, since this is not the only factor.”

The explanation seems to be correct - except for the fact that in the Northern Hemisphere (NH) the deflection is towards the left, or the North-West. The diagram below indicates this:

I also put a very rough approximation of the Indian peninsula as a triangle, with the East Coast making a shallower angle of 35°  at Kanyakumari, than the West Coast which makes an angle of 21°.
Also, Kanyakumari is at 8.08° N latitude.

Why does India’s West Coast get hit by cyclones less often than the East Coast? 

a)  Cyclones form over water, because they pick up energy from evaporating water 

b)  Cyclones are mostly observed to originate between 7 and 15 degrees of latitude; they form at latitudes greater than 7 degrees (in the NH), and do not originate at all in the zone of +/- 7 degrees about the Equator.

c)  Cyclones move counterclockwise in the NH because of the Coriolis force

d      The East Coast is at an angle to the cyclone so it tends to miss it. The position of Kanyakumauri at 8 degrees N is significant in view of c).  

     

       Another factor is the frequency of storms in the Bay of Bengal and in the Arabian Sea (4:1):

       .http://www.telegraphindia.com/1091112/jsp/frontpage/story_11731340.jsp

“       "Historical records suggest that for every four cyclones in the Bay of Bengal, there is one in the Arabian Sea,” said Basab Bandopadhyay, a scientist in the cyclone warning division at the India Meteorological Department, New Delhi.

Subtle differences between the way that convective currents behave over the Arabian Sea and over the Bay of Bengal may explain this higher frequency of cyclones forming over the Bay, scientists said."

http://www.indiaweather.gov.in/?page_id=281

Q: Why are there fewer cyclones in the Arabian Sea compared to the Bay of Bengal?

The Arabian Sea is relatively colder than the Bay of Bengal and this inhibits formation of cyclones.

"Bay of Bengal cyclones either originate in situ or come from the South China Sea (also NW Pacific) (the latter has 35% of all global cyclones every year, so this is a large number). Arabian Sea cyclones either originate in situ or are remnants of cyclones that come from the Bay of Bengal overland across the Southern Peninsula (and so have become weaker, and are less in number)." 

Generally storms do not cross the Equator - but this rule is probably not inviolable.

http://www.britannica.com/science/tropical-cyclone

"The developing (storm) system must be at least 500 km (300 miles) away from the Equator. For the development of the rapid rotation characteristic of tropical cyclones, the low-pressure centre must be located at least 500 km (300 miles) away from the Equator. If the initial disturbance is too close to the Equator, then the effect of the Coriolis force will be too small to provide the necessary spin. The Coriolis force deflects the air that is being drawn into the surface low-pressure centre, setting up a cyclonic rotation. In the Northern Hemisphere the direction of the resulting circulation around the low is counterclockwise, and in the Southern Hemisphere it is clockwise".

Note that the distance between Kanyakumari and the Equator is about 900 Kms. This implies that the cyclones that form in the Bay of Bengal and in the Arabian Sea are 'separate' - to some extent - because a cyclone crossing land tends to weaken (as mentioned above), but, again, this is not an insurmountable barrier, so there will be some crosstalk between the two.

A similar phenomenon - the East Coast getting more hurricanes - has been observed in the U.S.:

http://www.aoml.noaa.gov/hrd/tcfaq/G8.html

Why do hurricanes hit the East coast of the U.S., but never the West coast? Contributed by Chris Landsea (NHC)

"Hurricanes form both in the Atlantic basin (i.e. the Atlantic Ocean, Gulf of Mexico and Caribbean Sea) to the east of the continental U.S. and in the Northeast Pacific basin to the west of the U.S. However, the ones in the Northeast Pacific almost never hit the U.S., while the ones in the Atlantic basin strike the U.S. mainland just less than twice a year on average. There are two main reasons. 

The first is that hurricanes tend to move toward the west-northwest after they form in the tropical and subtropical latitudes. In the Atlantic, such a motion often brings the hurricane into the vicinity of the U.S. east coast. In the Northeast Pacific, a west-northwest track takes those hurricanes farther off-shore, well away from the U.S. west coast. 

In addition to the general track, a second factor is the difference in water temperatures along the U.S. east and west coasts. Along the U.S. east coast, the Gulf Stream provides a source of warm (> 26.5°C) waters to help maintain the hurricane. However, along the U.S. west coast, the ocean temperatures rarely get above the lower 20's, even in the midst of summer. Such relatively cool temperatures are not energetic enough to sustain a hurricane's strength. So for the occasional Northeast Pacific hurricane that does track back toward the U.S. west coast, the cooler waters can quickly reduce the strength of the storm."

Ok, so this is where I'm going to stop for today. I'll continue in the next post to add some more details about the Coriolis force. The reason that I have to go into more detail is that the deflection in the Northern Hemisphere is counterclockwise, but a cyclone can last several days, and in this process the continued CCW deflection causes the cyclone to trace a circle (called an inertial circle). So where does this leave us, going round and round? On an average is the motion of the cyclone an undeflected straight line (or whatever it was going to do anyway in the absence of the Coriolis force)?