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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 th…

Winds

Wind Atmospheric motion characterized by direction and speed. The
direction of the wind is the direction from which the wind
approaches the station (Example Northerly wind – Wind
approaching the station from North)
Gales A gale is a very strong wind (34 to 47 knots)
Squall A sudden increase of wind speed by atleast 3 stages on the
Beaufort Scale, the speed rising to force 6 or more, and
lasting for atleast one minute is called a squall
Gust A rapid increase in the strength of the wind relative to the
mean strength at the time

Monsoon
"MONSOON" has originated from the Arabic word "MAUSIM" which
means season. It is most often applied to the seasonal reversals of the wind
direction along the shores of the Indian Ocean, especially in the Arabian Sea,
that blow from the southwest during one half of the year and from the
northeast during the other.
Onset & Advance of Monsoon
The guidelines to be followed for declaring the onset of monsoon over Kerala
and its further advance over the …

Criteria to decide

Criteria for describing Hot Day for coastal stations
When maximum temperature departure is 5º C or more from normal, Hot Day
may be described irrespective of the threshold value of 40º C. If the threshold
value of 40º C is reached Heat Wave may be declared.
When a station satisfies both the Heat Wave and Hot Day criteria, then Heat
Wave should be given higher priority and be declared.
Hot Wind
Hot wind reduces moisture causing dehydration and a prolonged exposure
may prove to be fatal.
The phenomena of Loo over the plains of northwest India is very well known. It
is also described in the Weather bulletins and appropriate warnings are being
issued at present. The present practice should continue.
Criteria for Cold Wave
Wind chill factor plays an important role and brings down the actual minimum
temperature depending upon the wind speed. The actual minimum
temperature of a station should be reduced to "wind chill effective minimum
temperature (WCTn)" based on wind chill factor using the enclo…

Rainfall

The latest practices followed are summarised below:
Spatial Distribution of Rainfal l
Distribution No. of Places Description
Isolated One or two Places <25% of stations gets rainfall
Scattered At a few Places (26–50)% of stations gets rainfall
Fairly Widespread At many Places (51–75)% of stations gets rainfall
Wide spread At Most place (76–100)% of stations gets rainfall
Dry - No station reported rainfall
Intensity of Rainfall
Descriptive Term used Rainfall amount in mms
No Rain 0.0
Very light Rain 0.1- 2.4
Light Rain 2.5 – 7.5
Moderate Rain 7.6 – 35.5
Rather Heavy 35.6 – 64.4
Heavy Rain 64.5 – 124.4
Very Heavy Rain 124.5 – 244.4
Extremely Heavy Rain >244.5
Exceptionally Heavy Rain When the amount is a value near about the
highest recorded rainfall at or near the station
for the month or season. However, this term
will be used only when the actual rainfall
amount exceeds 12 cm.

Weekly/Seasonal Rainfall Distribution on regional scale
Excess Percentage departure of realised rainfall from normal
rainfall i…

sitemaps

http://ncert-notes.blogspot.com/
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Forecast

Types of forecast Description
Nowcasting A short range forecast having a lead time/validity
of less than 24 hrs
Short range forecasts Forecasts having a lead time / validity period of 1
to 3 days
Medium range
forecasts
Forecasts having a lead time /validity period of 4
to 10 days
Long range /Extended
Range forecasts
Forecasts having a lead time /validity period
beyond 10 days. Usually this is being issued for
a season. IMD issues Long Range Forecast for
southwest Monsoon rainfall and onset date for
Kerala, Northeast Monsoon Rainfall and Winter
precipitation over Northwest India.
Local Forecast In local forecast, whenever any weather
phenomenon is expected, its intensity, frequency
and time of occurrence is indicated. In the
absence of a weather phenomenon, the local
forecast describes anticipated sky conditions.
The other parameters for which the local forecast
issued include maximum temperature and/or
minimum temperature, rainfall, wind and special
phenomenon.
It is valid for a radius of 50 km around the stat…