GENERAL

CLIMATE

 [The section on "Climate" was supplied by the Meteorological Department of he Government of India, Poona.].

The climate of this district is typical of that on the west coast of India, with plentiful and regular seasonable rainfall, oppressive weather in the hot months and high humidities throughout the year. The summer season from March to May is followed by the south-west monsoon season from June to September. October and November form the post-monsoon or the retreating monsoon season. The period from December to February is the cold season.

Rainfall.

The district has a network of eleven raingauge stations with records extending to 82 years for most of the stations. Tables 1 and 2 give the rainfall data for these stations and for the district as a whole. The south-west monsoon commences by about the first week of June and the rains continue till about the beginning of October. The average annual rainfall for the district as a whole is 3,028.9 mm. (119.25"). The rainfall increases rapidly from the coast Howards the Western Ghats on the eastern border of the district. In the coastal strip the annual rainfall decreases from south to north. Uran and Alibag at the northern end of the coast get annually 2,072.3 mm. (81.58") and 2,080.8 mm. (81.92") of rain, respectively, Matheran gets as much as 5,167.5 mm. (203.45") of rain annually. Nearly 95 per cent, of the annual rainfall is received during the south-west monsoon months, and the

TABLE No. 1

NORMALS AND EXTREMES OF RAINFALL IN KOLABA DISTRICT

(a) Normal rainfall in mm. (b) Average number of rainy days (days with rain of 2.5 mm. or more).

TABLE No. 1-contd.

NORMALS AND EXTREMES OF RAINFALL TN KOLABA DISTRICT-contd.

continued..

*Based on all available data up to 1957.     †Years given in brackets.

rainfall in October forms the major portion of the rest. July is the month with the heaviest rainfall, the same being 38 per cent of the annual rainfall. The year-to-year variations in the annual rainfall of the district are not large. During the fifty-year period 1901 to 1950, the highest annual rainfall amounting to 138 per cent of the normal occurred in 1917. The very next year had the lowest rainfall in the fifty-year period and that was only 53 per cent of the normal. In seven years out of fifty, the rainfall was less than 80 per cent of the normal. Rainfall less than 80 per cent of the normal occurred in two consecutive years, 1904 and 1905 at all rainguage stations. At Roha, in 1906, rainfall was less than 80 per cent of the normal. Rainfall less than 80 per cent. of the normal occurred in 1924 and 1925 at Mangaon and Mahad. At Karjat 1920 and 1921 were the years with rainfall less than 80 per cent of the normal. It will be seen from table 2 that in 31 years out of 50 the annual rainfall in the district was between 2,600 mm. and 3,600 mm. (102.36" and 141.73").

On an average there are 94 rainy days (i.e., days on which the rainfall is 2.5 mm.-10 cents-or more) in year. This number varies from 82 at Uran and Alibag to 108 at Matheran,

The highest rainfall in 24 hours recorded at any station in the district was 657.3 mm. (25.88") at Matheran on July 24 in the year 1921.

TABLE No. 2

FREQUENCY OF ANNUAL RAINFALL IN KOLABA DISTRICT. (Data 1901-1950)

Temperature.

The only meteorological observatory in the district is situated at Alibag and data for this station may be taken as representative of the conditions generally prevailing in the district. Being a coastal district the diurnal (daily) and seasonal variations of temperature are not large. The period from March to May is one of increasing temperatures. May is the hottest month with a mean daily maximum temperature at 31.7°C (89.1°F) and the mean daily minimum temperature at 26.4°C (79.5°F). Fresh breezes from the sea relieve the oppressive heat particularly in the coastal regions in the afternoons. The onset of the south-west monsoon early in June brings down the temperatures slightly. After the withdrawal of the south-west monsoon by the end of September the day temperatures increase slightly and the weather in October and November is almost like the summer months. In the period from December to February the weather is cooler than in the post-monsoon months. The highest maximum temperature recorded at Alibag was 40°C (104°F) on April 19, 1955 and the lowest minimum was 9.4°C (49°F) on January 13, 1934.

Humidity.

The air is humid throughout the year. Relative humidity is on an average over 80 per cent. during the south-west monsoon season. In the rest of the year the relative humidity is between 65 per cent and 75 per cent.

Cloudiness.

During the south-west monsoon season skies are heavily clouded to overcast. In May and October the clouding is moderate. Clear or very lightly clouded skies are common in the rest of the year.

Winds.

Winds are very strong and blow from west or south-west during monsoon season. During the period from October to December winds are generally moderate but sometimes strong in October and blow from directions between north-east and south-east. In the three months from January to March the winds continue to be moderate and are predominantly from directions between north and east. In April while there is a slight strengthening of wind, the direction is variable. In May there is a further strengthening of winds and the directions are between south-west and north-west.

Special weather phenomena.

In association with cyclonic storms in the Arabian sea in the post-monsoon months and to a lesser extent in May, the district experiences very strong winds, sometimes reaching gale force, particularly very near the coast and also heavy widespread rain. Occasionally these storms may cross the coast in the northern part of the district and cause heavy damage. Thunderstorms occur in April and May and just before the onset of the monsoon and in the late September to the middle of November.

Table Nos. 3, 4 and 5 give the temperature and humidity, mean wind speed and frequency of special weather phenomena, respectively for Alibag.

TABLE No. 3

NORMALS OF TEMPERATURE AND RELATIVE HUMIDITY IN KOLABA DISTRICT

(ALIBAG)

*Hours I.S.T.

TABLE No. 4

MEAN WIND SPEED IN KILOMETRES PER HOUR, KOLABA DISTRICT

(ALIBAG)

TABLE No. 5

SPECIAL WEATHER PHENOMENA, KOLABA DISTRICT.

(ALIBAG)

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