Tuesday, May 15, 2018

South West Monsoon 2018 - Update #1 Parameters Check

Central,NW India heat LOW

As of now, the minimum pressure is around 1000 mb over NW India and into Central Pakistan. This should be around 998mb at this time of year. An upper-level WD trough is expected to touch N Pakistan and Kashmir during next 7 days, so this can marginally affect the heating over North India.  This LOW is expected to deepen slightly to 998mb during next 8 days.

Mascarene HIGH pressure system and Cross Equatorial Winds

At present the HIGH pressure over South Indian Ocean is WEAK around 1020mb and models suggest that the HIGH is not expected to materialize to around 1030mb during next 7 days.
This is why only weak cross equatorial winds are reaching Somalia coast and almost nothing crossing into South Bay. 


The Sea surface temperature along Somali coast has not started dropping below 28 C, meaning, the Somali low-level Jet is not present. Once the cross equatorial winds pickup, the Somali coast should see a drastic drop in Sea surface temperature. 

Bay Low and Arabian sea Low

The April month LOW over Bay has not materialized and it seems Bay is not in a mood to host one during next 10 days either. Instead, Arabian sea is expected to pop a LOW , circulation on 21-May.
Both, GFS and ECMWF are suggesting a Low over S-central Bay on 22-May and then intensifying into a Cyclone and moving NW.
This system will disturb the Bay Monsoon onset, as of now, it's not showing ANY sign of Monsoon onset over S,SE Bay and over South Islands of Andamans before 25-May.

LWD and North-South trough

At present LWD seen along W-ghats from S-tip Tamilnadu to NW Karnataka and along NE Andhra to SW,W Bengal , this is creating Afternoon, evening Thunder showers (pre-monsoon showers).

The seasonal N-S trough at low-levels from Bihar to S,SE Tamilnadu along SE coast of India should be well marked at this time of year, but it's not. At present the N-S trough can be seen as a mini N-S trough from S Madhyapradesh to E,central Andhra. Around 22-May, this is expected to align to the expected position.

Forecast for June, July and August
This is just for future reference purpose only !
JAMSTEC long range forecast indicates GOOD rainfall for SW,W coast of India during June, July and August.

And, CFS monthly forecast suggests the totally opposite. LESS, DEFICIENT rainfall during July, August for entire SW,W coast of India.
Let's see !!

Good MJO till 1st week of June

A good MJO phase is now moving into Arabian sea and will be over entire North Indian ocean , Arabian sea and South Bay till 1st week of June.
This is good for Monsoon onset !
This may be a reason for upcoming Arabian sea circulation around 22nd May.

Monsoon onset over South Andamans and SE,S Bay may get delayed and pushed beyond 25th May.
Monsoon onset over South Kerala can be around 2/3-June.