Monday, May 09, 2016

South West Monsoon 2016 - update #1 - parameters check, date for Andaman, Arabian sea, Bay LOW

El NiƱo is in its last stages

As of 24-Apr, the El Nino conditions are gradually easing and expected to be in Neutral state around 20-May-2016. Continuing with it, most models suggest that La-Nina conditions will be attained around end of June 2016.

Neutral & La-Nina conditions are GOOD for our South West Monsoon.

Indian Ocean Dipole (IOD)

At present the IOD is neutral and models suggest that it'll move into NEGATIVE condition from June. 
Pls note: Negative IOD events are more likely to occur during La Nina.
Negative IOD will mean more clouding over Eastern Indian Ocean and winds will be more focused towards it (meaning West to East). This can help our Monsoon, especially over Peninsula.
More about IOD and its effects.. click here

MJO for next 40 days

Latest MJO forecast suggests that WET phase for above equator Indian ocean from now to 18-May.
This can trigger a much needed LOW in Bay or Arabian sea to strengthen the cross-equatorial winds.

This latest satellite IR shows heavy clouding over S,SW,SE Arabian sea(all along 5N latitude) and into S,SW Bay, due to the current good wet phase of MJO.

Central,NW India heat LOW

As of now, the minimum pressure is around 1000/1002 mb over NW India and into Central Pakistan. This is marginally OK at this time of year. It should reach 994mb by end of May into June. Less WD frequency over N,NW India will make the heat LOW to deepen further during next 10 days.

Mascarene HIGH pressure system and Cross Equatorial Winds

As of now, the Mascarene HIGH over South Indian ocean is good with pressure around 1030mb. but the position is slightly SW to the expected position.
Models predict a sustain and eastward drift of this HIGH during next 5 days.
This is why, there's GOOD cross equatorial winds are seen reaching Somali coast. Due to present position of the HIGH, there's less (or) NO winds crossing equator into S Bay.

Sea Surface Temperature(SST) over Bay and Arabian sea

At present slight reduction of SST seen along South Somali coast due to presence of winds. Entire Somali coast should have a SST of around 20/21 C at the end of this month to have good Somali Jet.
Apart from this, most of Bay and S Arabian sea are having SST above 30 C, which is very good to host a circulation.
Bay circulation is the much needed one after 15/18-May.


In next 5 days...
Latest GFS expects that due to persistence of good cross-equatorial flow into SW,S Arabian sea, there's a possibility of circulation over SSE Arabian sea near Maldives and another near Somali coast itself. And expects nothing over S Bay, again due to presence of less or NO cross equatorial winds.

On the other hand ECMWF model suggests a perfect scenario for establishing cross-equatorial winds into S Bay. It suggests a circulation over SSW Bay in next 5 days and drifting WNW.
This kind of scenario happened last year around 10,11,12,13-May.. check our archives

LWD and North-South trough

At present, the LWD at low-levels over peninsula along W-ghats is OK, which is giving afternoon, evening T showers all along W-ghats, especially over Karnataka, Kerala and Tamilnadu ghats. This is also called as pre-monsoon T showers.
The N-S trough from N Bengal to S-tip Tamilnadu is less/not marked and should take shape soon rather than later. This is an important parameter to pull low-level westerly monsoon winds towards Peninsula.

200hpa JET
This upper-level jet stream should turn easterly upto 13/14N around end of May to establish necessary shear for the low-level westerly Monsoon winds.
As of now there's no easterlies in this 200hpa level. This should take shape towards 20-May.

Scary! Long range forecast from JAMSTEC

This forecast for June, July, August suggests BELOW average rainfall for most of India except for S,SW India, Andamans, East & NE states of India.
ALERT for Maharastra as it is already suffering from water shortage / drought !

Monsoon onset dates of Andamans, S,SW,SE Bay is depending the expected LOW over Bay/Arabian sea.
LOW over Arabian sea will mean a delay in onset over S,central Andaman Islands.
Kerala onset may be early !

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