Sunday, July 19, 2009

A low pressure area developed over northwest Bay of Bengal and off the Orissa/W.Bengal coast on Saturday. That is a day ahead of expectation. On sunday, it persisted,and became well marked. It is likely to intensify into a depression during next 24 hours.

Now, since the axis of monsoon trough at mean sea level, as on Sunday, passes through Ganganagar, Meerut, Bareilly, Gorakhpur, Dhanbad and center of well marked low pressure area and thence southeastwards to eastcentral Bay of Bengal, normally the system should move along the line of the axis.

(a):That means, after crossing the coast, it would move north-west. If so, the regions of U.P., and later Delhi,punjab and Haryana can expect rain sometime after the 22nd. In this case, Orissa, W.Bengal get initial heavy rain, and east M.P./Vidharbh get medium rain on 21st./22nd. till the system moves away.
But as I mentioned, it will depend a lot on the actual movement of the system, after intensifying into a depression. Because, there are contrary forcasts on its course of direction by different weather models.

(b):ECMRWF expects the depression to cross on the 22nd. and move west-northwest. That is towards M.P. In this case the north is avoided, and M.P./Maharashtra and later Gujarat get the brunt of rains.

(c): GFS today forecasts is movement to be restricted to the W.Bengal/Bihar region, before dissipating. In this instance, only Orissa/W.Bengal and Jharkhand will get the maximum benefit of the rains.
I personally feel, that tomorrow, the monsoon line of axis will slide southwards, and by the time the system crosses the coast for its inland journey, it will follow the new line-axis position. The monsoon axis should roughly be along the Rajasthan/M.P./Orissa line by tomorrow evening. (i am not putting this 4th. option as (d), since it is my personal view).

Bit confusing, I know, but one must be clear of the options possible before forecasting behaviour of a developing weather system.

Anywhichway, Konkan will get rains from Monday evening, and interior Maharashtra from Monday morning. Only in case of option (a) and (c), it will be shortlived, maybe for a couple of days, and lesser intensity.

Kerala, getting very heavy rains since the last 2/3 days, may see some relief now, as the moisture will concentrate along the northern regions of the west coast. In fact, the entire southern peninsula ( Bangalore included) may witness lesser rainfall for the major part of next week.

Mumbai on Monday will see passing showers between late morning and noon. Later, early evening will see the rain frequency increasing. Late evening/night outings may need rain precautions. Major bit of the 40 mms rain (cumulative) expected will be on Monday evening/night.

But, 40 mms is normally no cause for worry or panic. A decade ago (with less population and contructions), Mumbai was normal and flood free even with rains even upto 150 mms/day !

1 comment:

Anonymous said...

The moot question for a Mumbaikar from the perspective of the Bay depression under consideration is what happens on Thursday (23rd July) and Friday (24th July). Various agencies have given above normal High Tide warning for these days and hence even a moderate rainfall may cause problems.

For someone like me who had suffered significant financial losses during the 26th July floods, I will be keeping a close watch on the developing situation