Thursday, May 03, 2018

Monsoon Watch – 3 (Part 1)...2018 .....3rd May
Further Analysis of the parameters as discussed in MW-1,MW-2.
Position as on 3rd May :

1.Cross Equatorial Winds :
Let me explain, that the winds on crossing the equator break into 2 branches. i) gushing into the Arabian Sea, and ii) moving into the Bay of Bengal. 
wind flow on 3rd May 2018

i) In the Western sector Southern Hemisphere, winds are just picking up speed and hitting the East African coast, but no proper re-curving is seen. To get a defined Somali Current, we need a proper re-curving Northwards/North-East of the winds, on the Kenyan coast. The current SST off the Somali Coast is 26 c (above normal),while the required SST in first week of June is 19/20c. (Required to form masses of Monsoon clouds in the warm central Arabian Sea).

ii) In the eastern sector, in the Bay Branch, the cross equatorial winds are currently slightly  haphazard and disorganised. In the Bay along India coast , the winds turn Southerly. The winds hitting Sumatra coast are not Westerly (as required), and also need to gather strength soon.
We prefer the Bay Branch to be better organised, as the normal date for SWM to hit the South Andaman Sea is 15th May.

Mascarene high
 pressure zone in the South Indian Ocean.
Main High reading of 1029 mb and other high of 1027 mb are currently observed between Madagascar and Australia.

The "Power House" of the Monsoon winds is lower in strength (should be 1032 mb), for this time of the season.


 2. Seasonal Low: 

The NW plains heating picked up initially, and laxed again, as WDs started streaming in.
After the early summer onslaught,with 50c (Sindh Pakistan) in April itself, the heat decreased considerably over the North and west subcontinent after end April.

Over Northwest India, the max and min temps fell by 2-4c  from the levels seen after MW-2 (averaging max 43-45 c).
Severe Duststorms and Thunderstorms lashed Punjab, Delhi and U.P. and parts of North Pakistan last week.
After recording first  50 c temp in April(30th) in Asia, Shaheed Benazirabad (Sindh) is currently at 45.5 c and Jacobabad  44.5c.
Karachi was 44.1c on 3rd May !

A Western Disturbance is approaching.....

Past 7 days anomaly -
An East-West Divide in  Anomaly

Min temp was mostly in the normal range.

The seasonal Low, as a result has not shown good deepening, during MW 2 when it was 1002 mb

The pressure in the core region (Thar Desert / Sindh) is just touching 1000 mb mb. (In 2014 was 1004 mb, 2015 was 1000/1002 mb , 2016 it was at 1002 mb during this time). 

As mentioned, it normally should reach a low nadir of 994 mb in June in the Thar Desert, and with 1008 mb in the South Arabian Sea, a perfect gradient is created to attract the south -west winds towards the coast.
Core low pressure

 After this lull, the core low formation region (Thar desert) has to start to heat up again. Barmer/Jaipur recorded 41.5 c on 3rd May 2018. Delhi S'Jung recorded 35.2 c....Minimum was 19.5c !

The highest max temperature (46.0 c) over the subcontinent on 2nd May 2018 was recorded at Phalodi (Raj) and the highest min temperature (31.2 c) on 3rd May 2018 was recorded at Bikaner (Raj). Though in many Rajasthan towns, the minimum has dropped to 24-26c range. Ludhiana min was 18.8c (-3c below).


3. ENSO: This year also, like last year, we also base our observations on the Multivariate ENSO Index (MEI).  An attempt is made to monitor ENSO by basing the Multivariate ENSO Index (MEI) on the six main observed variables over the tropical Pacific. 

These six variables are: sea-level pressure (P), zonal (U) and meridional (V) components of the surface wind, sea surface temperature (S), surface air temperature (A), and total cloudiness fraction of the sky (C). (Negative values of the MEI represent the cold ENSO phase, a.k.a.La Niña, while positive MEI values represent the warm ENSO phase (El Niño).The MEI is computed separately for each of twelve sliding bi-monthly seasons (Dec/Jan, Jan/Feb,..., Nov/Dec). 

Negative values of the MEI represent the cold ENSO phase, a.k.a.La Niña, while positive MEI values represent the warm ENSO phase (El Niño).

The updated (Feb-Mar) MEI is at -0.502 (in Jan-Feb was -0.731), for a slightly decreased ranking.

30 day SOI has fallen further after MW2 and is now at  +3.0, while April 30th reading was +4.5.
90 day value is +4.4 ( sustained SOI of -7 to 7 is neutral. Above 7 is La Nina, and below -7 is El Nino ).
The Oceanic Nino Index (ONI) is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. ONI has remained same marginally after MW2 and latest value is -0.8 .
( ONI of -0.5 to 0.5 is neutral. Above 0.5 is El Nino, and below -0.5 is La Nina).

In the tropical Pacific, the El Niño–Southern Oscillation (ENSO) remains neutral—neither El Niño nor La Niña. All climate models indicate the tropical Pacific Ocean will continue to warm slowly, but temperatures will remain close to average through the Northern Summer Beneath the surface, the tropical Pacific Ocean is slightly warmer than average, but well within the neutral range...   

Indicator: ENSO Neutral (should be watched for El Nino development in August/September).

4. The Bay had hosted a pre-monsoon low during March 2018. 
As discussed, we should normally see a low sometime after the 15th of April.
But there has been no development after that. 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 currently a weak high ridge is observed. 

What is needed now is a pulse from the Far East. But,currently there is no storm or low pressure in the Philippines’ Seas.

A strong MJO would hasten the favourable formations and lows, with enhanced precipitation. 
The propagation of the MJO to the Indian ocean is uncertain over the next two weeks.
Another factor, which helps the winds gain strength, and bring more moisture into the Indian landmass, is the sea temperatures on both sides of the Peninsula. Optimum (warm) temperatures will hasten and create more clouds, and help in faster forming of the lows from the Bay.
Currently, the only sort of +ve sign is the above normal temps (30 c) of the seas surrounding the peninsula. But sea temps (29 c) near the South Andaman Sea have fallen below normal currently.

We prefer the Bay parameters to show fast progress, as the normal date for SWM to hit the South Andaman Sea is 15th May.
 Sea Temp Anomaly

Indicator: -ve

5. ITCZ / LWD :
To bring the existing SE winds above the equator (as SW) , the ITCZ should move northwards.Currently it is near the equator. During late April , it oscillated between equator to 5N.
A LWD in the central peninsula region "looks after" the moisture content in the interior areas, and prepares the atmosphere with the humidity required. In reality, this LWD remains till June, in variable phases, and finally merges with the Monsoon trough (axis)/ITCZ  when the ITCZ moves towards the Sub Continent.

Currently, the line of wind dis-continuity is located weakly as a trough, through the peninsula, from Interior Karnataka towards Kerala. It is giving adequate precipitation in the South peninsular regions. Outbreaks of pre- monsoon thunder showers which are expected normally in the southern states  are taking place.
In fact , a UAC over Bangladesh and Odisha is running a trough SW towards Eastern India, bringing very heavy showers.Violent storms lashed West Bengal and Odisha (Daily details on our Twitter Handle)

Indicator: Normal

6.Jet Streams :

The 200 hpa Jet streams over the subcontinent is the additional parameter to be watched from MW-3 .
The jet streams are to be followed as the westerly jet core shifts to the north and easterly jet stream is formed, over the course of late summer, progressively from south to north of the subcontinent , heralding the progress of south-west monsoon over the subcontinent.

Currently are getting into the easterly trend, south of 10 N latitude.
They are required to strengthen to easterlies at those latitudes in the coming days, for heralding the SWM to the South Andaman Sea.
During last week, its core oscillated between Lat 26°N to 30°N with the wind speed varying between 79-130 kts around 186 hPa to 227 hpa. The highest wind speed of 130 kts at 186 hPa was recorded over Patiala on 20 th. 

The westerly jet core shifts north of the Himalayas during the southwest monsoon season, as the jet streams turn easterly over the subcontinent.

Indicator: Normal

So, overall, we can summarize as:
Parameter: MW-1:  1) -ve  2) -ve  3) Neutral  4) -ve 
                  MW-2:  1) -ve  2) -ve  3) Neutral  4) -ve  5) Normal
                  MW-3:  1) -ve  2) -ve  3) Neutral  4) -ve  5) Normal  6) Normal

*But, situations can change fast, and by the time we discuss the next  MW, some factors can suddenly become +ve or -ve. So, MW discusses and follows the developments as they emerge, and discuss the parameters as is where are. 

Monsoon Watch should not be used/depended upon commercially or otherwise. Monsoon Watch Series may differ from other models.)

Looking at the current parameters, there seems slight delay in the South West Monsoon arrival dates for Andaman and Kerala as of now. 

But would like to wait for another 4 days to see any changes in parameters, so MW-3 Part 2 will be published 7th May (Brief write up with estimated dates of SWM arrival).

The quantum of rainfall expected will be analysed in the subsequent MW-4, which will be ready for publication on 16th May.


Vinod Desai said...

Seems pre monsoon activity is very strong this year..storms in north india..heavy rains in east india..even south india has been getting good showers..

NilaY Wankawala said...

Nice indepth follow up as ever sir

Rohit Aroskar said...

Wonderful analysis as always

Kaneyen said...

As usual, it is very interesting to read. Hats of to you sir. My observation of wind REVERSALS in TN from NE to SOUTH and then SW. This time towns along EASTERN GHAT received very heavy pre monsoon rainfall in Krishnagiri, Vellore, TVmalai, Villupuram, Dindigul districts etc. Though it is NORMAL the winds were predominantly SOUTHERLY.

Rawat said...

There is lots of taking about storm in NW India. Please share your view.

Sunny said...

Delhi gets good pre monsoon showers n drizzles ..but when the actual monsoon sets in the rains disappear from the capital

Strong Western Disturbance is seen affecting the country and the subcontinent. Heavy rain and snow reported from Himalayas, and rain/thunder...