Photo: Collected
Rain is falling in various areas of the country right at the start of October. However, the Bangladesh Meteorological Department says there may be less rainfall than normal over the month as a whole. At the same time, the agency has also spoken of the risk of a cyclone forming in the Bay of Bengal this month.
The long-range forecast for October says two to three low pressure areas may form this month, one of which may turn into a depression or a cyclone.
According to the forecast, the south-west monsoon may withdraw from Bangladesh in the first half of October itself. Day and night temperatures may gradually fall in the second half. In addition, there is also a possibility of thunderstorms on three to four days during the month.
Meteorologists said that after the monsoon’s withdrawal, besides the tendency for rain easing, temperatures will also begin to drop towards the end of the month.
But why is it raining at the start of October? How much longer will this rain continue? And why is the fear of a cyclone being spoken of amid the forecast of less rain?
Why it is raining, how long it will last
In the context of Bangladesh, October is the time when the monsoon ends and the dry season begins. At this time the monsoon gradually begins to withdraw and the influence of the western winds, or westerlies, associated with winter weather starts to grow.
Meteorologist Md Tariful Newaz Kabir said the monsoon is still active over Bangladesh. Although the monsoon usually begins to withdraw within the first 10 days of October, this time its flow still remains.
Recently a well-marked low near Myanmar and the south-eastern region of Bangladesh had turned into a depression, because of which the normal flow of the monsoon was somewhat obstructed. Although that depression has become inactive, the monsoon flow has not stopped completely; on the other hand, the westerlies too are gradually advancing.
Tariful Newaz Kabir’s explanation is that when the monsoon leaves, the westerlies will come, and then temperatures will gradually keep falling. Now both wind flows are trying to occupy the space, so although the monsoon flow is there, it is comparatively weak. With water vapour coming in sporadically along with this, clouds are forming in various places and rain is falling.
By his reckoning, such a situation may persist for another four to five days, and during this time the tendency for rain will be comparatively higher in the eastern region of the country.
In the next 24 hours, rain or thundershowers may occur at various places in Khulna, Barishal, Chattogram, Sylhet, Dhaka and Mymensingh divisions. During this time Rangpur and Rajshahi may remain comparatively dry, although the tendency for rain may later increase in these two divisions too for a day or two. After that, rainfall will ease considerably across the whole country.
According to this meteorologist, the rain will decrease from after 10 October and temperatures may then rise somewhat, because even though the rain eases, the sun has not yet moved very far south. However, temperatures will gradually begin to fall towards the end of the month.
In his view, temperatures at the start of winter this time may be somewhat higher than in other years. Because of El Nino, there will be a warm winter globally this year, meaning temperatures will not be very low. Although in other years temperatures were seen to drop right after the rain, this time it will take a little while.
Why the fear of a cyclone even as rain eases
The Meteorological Department’s month-long forecast says two to three low pressure areas may form in the Bay of Bengal in October, one of which may turn into a depression or a cyclone. However, there is no scope to say specifically right now where the possible cyclone will form, what its track will be or whether it will affect Bangladesh.
Generally, the tendency for cyclones to form in the Bay of Bengal exists in the periods before the monsoon arrives and after it withdraws.
Tariful Newaz Kabir says that since the time for the monsoon’s withdrawal has now come, this is also a normal time for cyclones to form. In past years too, major cyclones have hit Bangladesh in October-November. In other words, there is no inconsistency between the rain easing and the fear of a cyclone.
He said the pattern of monsoon rain this time was somewhat different compared to the past few years. In the last three to four years there was comparatively less rain at the beginning of the monsoon, but it would increase in September-October. But this time there was plenty of rain in June, July and August, some in September too, and the tendency for rain has begun to ease since then.
In his view, although June to August are Bangladesh’s rainy months, for several years there was almost no rain during this period, and it came right at the end. This time nature has followed its own rule, which he considers positive. However, he also noted that under the influence of El Nino the amount of rainfall has eased somewhat towards the end of the year.
Source: BBC Bangla
