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Tuesday, January 26, 2010

Specifications for activity/ strength of Northeast Monsoon

Weak Monsoon:

Rainfall less than half the normal.

Normal Monsoon:

Rainfall half to less than one and a half (1½) times the normal.

Active Monsoon:

i) Rainfall 1½ to 4 times the normal.

ii) Rainfall in atleast two stations should be 3 cm in Coastal Tamil Nadu and

south coastal Andhra Pradesh and 2 cm elsewhere.

Iii) Rainfall in that sub-division should be fairly widespread or widespread.


 

Vigorous Monsoon :

i) Rainfall exceeding 4 times the normal.

Ii) Rainfall in atleast two stations should be 5 cm in Coastal Tamil Nadu and

south coastal Andhra Pradesh and 3 cm elsewhere.

Iii) Rainfall in that sub-division should be fairly widespread or widespread.

Strength of Southwest Monsoon

Descriptive term over the Sea

Wind speed (in knots) reported or inferred to be existing.

Weak monsoon Upto 12 knots

Moderate monsoon 13 to 22 knots

Strong monsoon 23 to 32 knots

Vigorous monsoon 33 knots and above.

Descriptive term over land area

Weak monsoon

Rainfall less than half of the normal.

Normal monsoon

Rainfall half to less than 1½ times the normal (mention of

'normal' monsoon may not be necessary in general).

Active/ strong monsoon

i) Rainfall 1 ½ to 4 times the normal.

ii) The rainfall in at least two stations should be 5 cm, if that

sub-division is along the west coast and 3 cm, if it is

elsewhere.

iii) Rainfall in that sub-division should be fairly widespread to

widespread.

Vigorous monsoon

i) Rainfall more than 4 times the normal.

ii) The rainfall in at least two stations should be 8 cm if the

sub-division is along the west coast and 5 cm if it is

elsewhere.

iii) Rainfall in that sub-division should be fairly widespread or

widespread


 

While describing the activity of the monsoon,

i) The normals of stations, when ever available should be used.

ii) Till normals for all the stations are available the following procedure

should be adopted:

Number of stations in a sub-division with normals a

Normal for these stations b

Average normal for the sub-division b/a

Total number of stations reporting rainfall c

Actual total rainfall reported by these stations d

Therefore, the average rainfall for the sub-division d/c

Compare d/c with b/a and describe the activity of the monsoon

accordingly, other conditions being fulfilled.

3. i) In the sub-divisions, w here the percentage of hill stations is high, the

hill stations must be also taken into account for describing the activity of

the monsoon. In other sub-divisions, the hill stations will be excluded.

ii) The monsoon activity will be described in all the sub-divisions of

northeast India as is done for sub-divisions of other regions.

iii) The monsoon activity need not be described over the Bay Islands and

the Arabian Sea Islands.

Subdued Monsoon activity

1. Whenever, a country wide dry spell continues for more than 3 days and

is expected to continue for atleast 2 more days, the description of

monsoon should be given as 'weak or subdued monsoon for the

country as a whole. RC level bulletins may also include this information.

2. Information on prolonged dry spells/ subdued activity over the met.

subdivisions also should be included in the RMC/ MC level bulletins if

such a spell is persisting for 2 or more days and is expected to

continue.

3. Monsoon activity for a sub-division might be considered subdued if the

rainfall realised is less than ½ the normal

Nomenclature for different parts of the day

Early hours of (date) 0000 – 0400 hrs, IST

Early morning 0400 – 0600 hrs. IST

Morning 0400 – 0800 hrs. IST

Forenoon 0800 – 1200 hrs. IST

Around noon 1100 – 1300 hrs. IST

Afternoon 1200 – 1600 hrs. IST

Evening 1600 – 2000 hrs. IST

Night 2000 – 2400 hrs. IST

Terminology used for state of Sea

Descriptive term : Height in –Metres -Wind speed in knots (kmph) –Beaufort scale

Calm ( glassy) 0
0
0

Calm (rippled) 0 - 0.1 1 - 3 ( 2 - 6) 1

Smooth (waveless) 0.1 - 0.5 4 - 10 (7 - 19 ) 2 - 3

Slight 0.5 - 1.25 11 - 16 (20 - 30 ) 4

Moderate 1.25 - 2.5
17 - 21 ( 31 - 39) 5

Rough 2.5 - 4.0 22 - 27 (41 - 50) 6

Very rough 4.0 - 6.0 28 - 33 (52 - 61) 7

High 6.0 - 9.0 34 - 40 (63 - 74) 8

Very high 9.0 - 14.0 41 - 63 (76 - 117) 9 - 11

Phenomenal Over 14 64 or above (119 or above-12

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