tropical cyclone (with special reference to the Indian sub-continent)

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Tropical cyclones are warm core vortex circulation of tropical region with a small diameter, often of an approximately circular shape, minimum surface pressure (<900mb 33m="33m" accompanied="accompanied" amp="amp" at="at" by="by" least="least" maximum="maximum" o:p="o:p" of="of" rains="rains" sec.="sec." standard="standard" thunderstorms="thunderstorms" torrential="torrential" winds="winds" with="with">
& are known by a variety of names.
                                                              these storms cause havoc in the India, Bangladesh, Myanmar & hence, correct predictions are required for preventions for disaster management policy formulation.
There are 3 distinct periods for occurrence of this storm:-
1) Pre-monsoon period;
2) Monsoon season leaving the months of June, July, August & September.
                      On an average 13 disturbances develop over Bay of Bengal & 10% occur in the pre-monsoon season. January - March is normally free from them.
Location & direction of tracks:-
they show different locations & different tracks in different season.
Season-monsoon
a)formation-northern bay of Bengal.
b) movement-west,nort west.
they occur west of 12(degree)East & 16 (degree)North-21(degree)North in the month of June.
In July-storms move along a westerly track. It lies generally between 20(degrees)north-25(degrees)north & it's incidence of recurvating the Himalaya’s foothills is rare.
In May-storms show recurvature tendencies & there are certain regions where recurvature is frequent. It is difficult to predict the pre-& post-monsoon periods.
Illustration:-(period 1891-1960)
Months
Number of storms over Arabian sea
Number of storms over bay of Bengal
Jan.-Feb.
5
2
Mar.-Apr.
22
5
May-June
62
26
July-Aug.
63
4
Sept.-Oct.
80
21
Nov.-Dec.
82
24
The characteristics of these storms are not uniform. Many of these storms have varied velocity upto 33 knots.some of these are passed into storms of 34-37 knots. a few of these develop into severe tropical storms of 48-63 knots & very few turn into Hurricanes of >64 knots.
  characteristic feature of cyclonic disturbances observed:-(1976)   
1)10 cyclonic storms & 3 depressions form in Bay of Bengal & Arabian Sea per year.
2)5 storms have a westerly to N.W. tract & 3 on northernly tract while remaining 2 recurved.
3) Most were of small size with area of gale force confined to <1 centre.="centre." degrees="degrees" from="from" o:p="o:p" the="the">
4)All disturbances could be traced back to the south china sea.
5)Parts of Gujarat, Andhra Pradesh, gangetic west suffered considerable damage due to this cyclone storm.
6)"Masulipatam cyclone" retained it's intensity over land for more than 500 Km.
7) severe storm which hit Bay of Bengal islands towards the end of December was a very rare occurence. It also gave an all time record rainfall at some of the islands & caused damage in little Andaman & Niccobar islands. The deep depression that moved from Bay of Bengal(northern) to Himachal Pradesh in mid-Aug. 1976 attained intensity of a cyclonic storm temporarily when it was close to Delhi.

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