Sunday, April 19, 2009

Monsoon Watch -5

The first "low" of the season, which formed last week in the Bay, intensified into a cyclone "Bijli". But, the cyclone was short lived, and after interacting with the ridge aloft, fizzled out over the Bangla Desh region within a day.

No harm done for the monsoon build up !

The streamline map indicates not much disruptions due to the cyclone. A few marked developments observed :


1. The south-easterlies from below the equator, required to hit the Indian coast as the South-West monsoon current, have picked up in the eastern -most segments of the bay. Though still initial, it shows good recurving to the south-west direction over the southern coast of Myanmar.


2. The Intertropical Convergence Zone (ITCZ), also known as the Intertropical Front, Monsoon trough, is a belt of low pressure girdling Earth at the equator. It is formed by the vertical ascent of warm, moist air from the latitudes north and south of the equator.The location of the ITCZ varies throughout the year and while it remains near the equator, the ITCZ over land ventures farther north or south than the ITCZ over the oceans due to the variation in land temperatures. The location of the ITCZ can vary as much as 40° to 45° of latitude north, as in the Indian monsoon season, or south of the equator, as in winter, based on the pattern .


The ICTZ is normally required to cross the equator (from the southern hemisphere), by around the 1oth. of May. From that date onwards, it moves northwards gradually, and the monsoon trough gets embedded in it. By the 15th. of May, the bay segment of the ICTZ nears the Andaman Islands, thereby starting the monsoon.

The streamline map shows the ICTZ today. At the extreme west, near 40 E, it is almost at the equator. There onwards, it slopes southwards almost to the Australian coast.


3. A line of dis-contiunity has re-appeared in the southern Indian peninsula. With this emerging again, a fresh flow of easterlies will re-enrich the southern areas with the much needed "pre monsoon" moisture in the atmosphere.


Good indications and positive parameters for the monsoon.


The other good sign is the heat wave in Rajasthan/Gujarat and Maharashtra. Though the seasonal low over the sindh/rajasthan region has not yet started forming, it can be expected to form around the normal time this year, i.e. by the 3/4 week of April.


Todays day temperatures are projected in the map. A 45c at Akola, surrounded by a number of cities recording between 42-44c.


See the map. The west coast seems to be in the midst of "winter" comparitively !!



The El-Nino phenomena is forecasted to be "neutral" throughout the June/July /Aug. period
Hence, the monsoon can be expected to be normal. As the ''neutrality" increases after June, the first month of the monsoon may experiance heavy rainfall.


Conclusion: Monsoon may arrive on time. Around 15th. May in the Andamans, 1st. June over Kerala, 8th. June over Maharashtra.


Weather Over the Garhwal/Kumaon Hills for the next 10 days.
A short spell of rain is expected over the hills and plains of Utteranchal on the 21st/22nd. Thereafter it will be mainly dry with no major system approaching till the 1st. of May. The period from 23rd. to 30th. will see a rise in day temperatures.

In the first week of May, we may see some thundershowers on a couple of days.

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