Saturday, April 24, 2010

Monsoon Watch - 3
Bay of Bengal : Indicator: -ve

Continuing from MW-2, I am now worried about the "Bay of Bengal" low pressure parameter. I feel, the Bay should host a pre-Monsoon low anytime after 15th. April. Like I mentioned in the previous MW, last year we had a cyclone in the Bay by the third week.
As on today, this region still maintains a luke warm response to the formation of a quick low. The pressure is anything but low, and the winds indiacate a "high" trying to establish itself. only +ve sign of a quick formation is that the SST is conducive. Conducive , 1)as I see winds getting Easterly, (See chart) to start with and breaking up the high pressure area, and 2) the Bay sea temperatures heating up around the Andaman Islands.


Sub-Continent Seasonal Low: indicator: ++ve
On the other hand, the sesonal low in the Thar region is getting into shape fast, thanks to the intense heat wave.True,the entire sub-continent region has suffered a heat wave, but the gains are much more. The central core pressure around the Thar desert region is now 1000mb (994mb required by June begining). And , as per the scheduled development, a proper gradiant is well on its way in the making.
The line of dis-continuity is shifting back to its normal postion, in the centre of the Southern Peninsula region. Out breaks of pre- monsoon thundershowers are expected next week in thie southern states and South Maharashtra.


Cross Equatorial Winds : Indicator ++ve
The cross equatorial wind flow, has picked up superbly in the Southern Hemisphere.Winds,getting stronger,have now started hitting the East African coast, and a re-curving Northwards of the winds, on the Kenyan coast,is seen.
As a result, we are seeing the Somali Current building up now.
Cross winds in the Eastern Sector (Bay) are getting strong too, and are re-curving.
That means, a high pressure region, the back-bone of our Summer Monsoon, is starting to form down in the Southern Hemisphere, off the Madagascar Island, and in the mid South Indian ocean. We have to observe this, and if no low pressure forms there till end of April, the ITCZ can start moving North.


Amidst this, a cyclone, "Sean" has formed off the west coast of Australia. Now, this would keep the ITCZ intact and keep it firmly stuck at around 5S. But, the forecast states the cyclone to move east, and dissipate within 72hrs. That's good news.
The positive news from Australian Weather Bureau; "The risk of tropical cyclone formation in the Australian region remains a very slim possibility for the end of April, although is becoming increasingly unlikely."


El-Nino: Indicator: Same as Last MW.
 El Niño is present across the equatorial Pacific Ocean. The latest weekly SST departures are:
Niño 4 0.8ºC
Niño 3.4 0.8ºC
Niño 3 0.8ºC

Niño 1+2 1.1ºC
For El-Nino Factors in detail, see Link
The monthly SOI for March was -11, but the 30-day Southern Oscillation Index [SOI] to 18 April was +10. Hence, the SOI, animportant factor for the El-Nino, has stayed +ve.

SST in the El-Nino zone are coming to normal levels very slowly. It should neautralise within 2/3 months.
If, by any chance, there is a delay in the El-Nino coming to normalcy, the set back would be, weak rains in June, picking up in July.
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