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Bangladesh has a tropical monsoon climate characterized by rain bearing winds, moderately warm temperatures and high humidity. Winter is mild, dry and sunny with average daily temperatures ranging between 50-80 degree F (10-27 degree C). January is the coolest month in the winter season which lasts from November to February. During winter, the eastern half of the country receives an average of less than 7 inches (180 mm)of rain, and the northwest receives less than 3 inches (75 mm). April and May, the season of little rains, that are important to farmers waiting to plow their fields for an early crop, bring more than 150 inches (380 mm) of rain to the eastern half of the country. This is the hottest season of the country with an average daily maximum temperature of around 90 degree F(32 degree C) and a minimum temperature of 70 degree F (21 degree C). The rainy season properly extends from June to October when the monsoon air stream sweeps in from the Bay of Bengal. During this time, Bangladesh receives heavy rainfall. Except for some parts in the west, it generally exceeds 60 inches (1500 mm) annually. Large area of the south, southeast, north and northeast receive 80-100 inches, and northern and northwestern part of Sylhet area receive 150-200 inches. Although temperature do not exceed the high 80's on most days during the season, they vary only slightly and may fall by only 10 degree F at night. The rainfall in April, September and October is crucial to the farmers. Without April showers to soften the ground, farmers may have to delay sowing the early rice crop - Aus, and major cash crop - jute. The little rains are erratic in an incidence and variable in quantity with concequent uncertainity for agricultural production. Failure of the late rains can seriously reduce the main crop - rice. The condition of lowest atmosphoric pressure occure in June and July. Winds are mostly from the north and the northeast in winter, blowing at a rate of 1-2 miles per hour in the northern and central areas and 2-4 miles per hour near the coast. During the period of northwesters (March - May), wind speed rises to 30-40 miles per hour. The coastal districts of Bangladesh, particularly those flanking the Meghna estuary, are susceptible to serious damage from cyclones, which cause major losses of life and property. In the early summer (April and May) and late in the monsoon season (September to November) storms of very high intensity often occure. They may create winds with speed of 100-150 miles per hour piling up the waters of Bay of Bengal to crests as high as 20 feet that crash with tremendous force onto the coastal areas and offshore islands. Since the early 18th century, when records were first kept, more than one million people have been killed in such storms --815,000 of them in three storm occuring in 1737, 1876 and 1970. Severe storms also occured in May 1985 and April 1991. Lesser hazards in the region are hailstorms, particularly in March and April, and tornadoes.
MAXIMUM AND MINIMUM TEMPERATURE AT SECLECTED CENTER
Center 1990 1991 1992 1993
Max. Min. Max. Min. Max. Min. Max. Min.
Barisal 35 8 36 9 35 12 36 7
Bogra 38 7 38 7 37 9 36 6
Chittagong 35 11 35 11 37 12 37 10
Comilla 36 8 36 8 34 12 36 8
Dhaka 35 11 39 10 39 10 37 7
Dinajpur 36 7 38 7 41 7 37 7
Faridpur 36 9 39 9 38 11 37 7
Jessore 37 7 38 7 39 11 38 6
Khulna 37 8 37 8 39 8 37 7
Mymensingh 36 7 37 6 38 10 35 8
Noakhali 35 11 36 11 34 14 35 9
Rajshahi 40 6 40 5 43 8 40 5
Rangamati 36 10 37 9 35 13 36 7
Rangpur 36 8 37 7 40 9 36 7
Sylhet 36 8 37 8 36 9 34 9
Storm warning signals in Bangladesh Storms generally occure in Bangladesh in the months of April-May and October-November (early part). The Meterological Department uses different codes of signals for storm warnings at maritime and riverports. These codes are given below in abbreviated forms. It should be noted that the signal numbers in the two codes do not carry the same significance and, in particular, that higher signal numbers within the danger and great danger maritime groups indicate differences in storm location, not difference in storm intensity. Storm warning signals for use at maritime ports:
a) Distance signals :
1. Cautionary There is a region of squally weather in which
a storm may be formed.
2. Warning A storm has formed.
b) Local signals :
3. Cautionary Port is threatened by squally weather.
4. Warning Port is threatened by a storm, but danger not yet sufficiently
great to justify extreme precautionary measures.
5-7. Danger Port will experience severe weather from a storm
of slight or moderate intensity.
5. Storm expected to cross the coast to the south of the port.
6. Storm expected to cross the coast to the north of the port.
7. Storm expected over or near the port.
8-10. Great Danger Port will experience severe weather from a storm
of great intensity.
8. Storm expected to cross the coast to the south of the port.
9. Storm expected to cross the coast to the north of the port.
10. Storm expected over or near the port.
c) Failure of communication :
Communication with the meteorological Warning Center have broken
down, and the local officer considers that there is danger
of bad weather.
Storm warning signals for use at river port:
1. Cautionary : Area threatened by squally winds. Look out for further development.
2. Warning : A storm or northwester is likely to strike the area.
3. Danger : A storm will soon strike the area. All vessels seek shelter
immediately.
4. Great Danger : A violent storm will soon strike the area.
Wind speed estimation over land in Bangladesh according to Beaufort scale
No. Name Indication Wind speed (MPH)
(at 33 ft)
1. Calm Smoke rises vertically Less than 1
2. Light air Wind direction shown by smoke 1-3
drift, but not by wind-vane.
3. Light Breeze Wind felt on face. Leaves rustle, 4-7
wind-vane moves.
4. Gentle Breeze Leaves and small twigs in constant 8-12
motion. Light flag extended.
5. Moderate Breeze Dust and loose paper raised 13-18
6. Fresh breeze Small leafy trees away. Small waves 19-24
on water. Surfaces from crests.
7. Strong breeze Large branches sway. Telephone wires 25-31
whistle. Difficult to use umbrella.
8. Moderate gale Whole trees sway. Difficult to walk 32-38
against the wind.
9. Fresh gale Twigs broken off trees. Wind 39-46
impedes progress when walking.
10. Strong gale Branches broken off trees.Slight 47-54
structural damage to buildings
( chimneys, roof slates, etc. ).
11. Whole gale Trees uprooted. Considerable 55-63
structural damage to buildings.
12. Storm Widespread damage to trees and 64-75
properties.
13. Hurricane Widespread damage to trees and Above 75
properties
In Bangladesh, wind speed of hurricane force occure in cyclones and tornadoes. Wind
speeds in line-squalls (nor-westers) are generally of forces 6-8, occasionally 9-10.
This page was first created on 12th of September, 1997 and
is maintained by Muhammad A. Mehedi. |
