Saturday, April 23, 2011

Monsoon Watch – 3

Bay of Bengal : Indicator: -ve

Continuing from MW-2, "Bay of Bengal" low pressure parameter is a worrying factor. Normally, 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, and in 2009 a cyclone crossed the Bay on 12th April.

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 indicate a weak "high" trying to establish itself. What is needed now are winds getting Easterly, to start with, and break up the existing high pressure area.

Only +ve sign of a quick formation is that the SST is conducive. Map shows around 32c near the Andaman Islands. Ideal temperature for quick low formation.

However, The region below the equator in the Bay sector continues to be favourable with SE winds tending to bend SW South of the Bay in the 95E region.

Remember, the normal date for SWM to hit the South Andaman Sea is 15th. May.

Sub-Continent Seasonal Low: Indicator: - -ve

The line of dis-continuity should shift back to its normal position, in the centre of the Southern Peninsula region.

Out breaks of pre- monsoon thundershowers are expected normally in the southern states and South Maharashtra. We are having these now. Though the showers in the South are heavier than normai, and excessive. But, a break in the pre-monsoon thundershowers is common, and will allow the days to get hotter.

An exception this year is the Vidharbha region.With exceptionally heavy rians, and more quantum wise, the temperatures are just about managing 40c, in fact just hovering around the high 30s. Normally Vidarbha is a hotbed ! 45-47c is a "kid's playground" for the region.

Nights last year were terrible at this time. See in this link, check dates April 13th and April 20th.

And contrast this with the lows today.

The sesonal low in the Thar region is also lagging behind, thanks to the absence of intense heat waves. The days, have started to rise now. Trends of rising temperatures are finally seen in Gujarat and adjoining regions of Sindh across the border. Just saw the 1st 45c on Saturday, 23rd.April. (See write up below the MW-3)

True, the entire sub-continent region has to suffer a heat wave, but the gains are much more. The pressure around the Thar desert region is now 1006mb (994mb required by June beginning). There is no central core formed as yet. And ,as per the required scheduled development, a proper gradient is behind schedule in the making.

Cross Equatorial Winds : Indicator: neutral.

The cross equatorial wind flow, has just about picked up in the Southern Hemisphere. Winds, have not yet achieved the required speeds, but just about started hitting the East African coast. Re-curving Northwards of the winds, on the Kenyan coast, is yet to occur.

That means, a high pressure region, the back-bone of our Summer Monsoon, is also slow to form down in the Southern Hemisphere, off the Madagascar Island, and in the mid South Indian ocean.

However, Cross winds in the Eastern Sector (Bay) are getting strong, and are re-curving.

Amidst this, no cyclones are likely to form off Australia this season. If no low pressure forms there till end of April, the ITCZ can start moving North. And with low pressure and ITCZ moving North, the High in the Southern Indian Ocean has a fair chance of getting stronger and anchoring well.

As the ITCZ tracks north, associated MJO waves can "ride" alongwith. Meaning, after the shift, more MJO waves in the Northern Hemosphere (read Bay regions).

The positive news from Australian Weather Bureau; " it is likely that the next MJO event to progress into the Maritime Continent region will have little influence on rainfall and tropical cyclone activity in the southern hemisphere, but more likely will begin to influence northern hemisphere weather patterns."

La-Nina: Indicator: Same as Last MW.

La-Nina is almost the same as reprted in MW 2. Not much significant warming is seen in the region.

The 30-day Southern Oscillation Index (SOI) to 16 April was +26.5.

SST in the La-Nina 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 La-Nina coming to normalcy, it would mean more than normal rains in June, decreasing in July.

Conclusion: As of today, there seems to be a slight delay in the Arabian Sea branch of the Monsoon. And, the Bay branch needs a little trigger to get going. Maybe a little less rain in the first half of June for Kerala, Karnataka (coastal) and S.Konkan? Arrival date should be around 4/5th June for Kerala.

(This Monsoon chase is my personal view, and my personal analysis and deciphering is done as per my assumptions).

1 comment:

Anonymous said...

there appears to be definite delay in onset, but difficult to predict jun at this stage!........Cdr Potey

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