Monsoon
Watch – 3 (part 1)...2017 .....4th May
Further
Analysis of the parameters as discussed in MW-1,MW-2.
Position
as on 4th 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 4th May 2017
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 haphazard and disorganised. In
the Bay along India coast , the winds turn Southerly, due to a weak High
Pressure in the Bay.
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 1025 mb and other highs of 1021/1022 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.
Indicator:-ve.
2.
Seasonal Low:
The NW plains heating picked up initially, and laxed again,
as WDs started streaming in.
After
the early summer onslaught, the heat decreased considerably over the North and
west subcontinent between MW-2 and MW-3 period.
Over
Northwest India, the max and min temps fell by 5 -10 c from the levels seen
during MW-2 (averaging max 46 c / min 30 c ).
After
recording first ever 50 c temp in April(19th) in Asia, Larkana (Sindh)
is currently hovering at 41.5 c.
Past
7 days anomaly -
North ,west ,central India was in the normal range.
Min temp was in the normal range.
The seasonal Low, as a result has weakened
considerably. Had
shown good progress during MW 2 when it was 998/1000 mb.
The
pressure in the core region (Thar Desert / Sindh) is just touching 1006 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
a lull, the core low formation region (Thar desert) has started to heat up
again.
Barmer recorded 42.8 c on 3rd May 2017.Delhi AP recorded 41.1 c.
The
highest max temperature (45.2 c) over the subcontinent on 3rd May
2017 was recorded at Banda (UP) and the highest min temperature (30.6 c) on 4th
May 2017 was recorded at Barmer (Raj).
After
a lull, the minimum temperatures have also increased over the subcontinent and
have just started touching the 30 c mark .
Indicator:-ve.
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 -0.08 (in Jan-Feb was -0.056), for a slightly
decreased ranking.
30 day SOI has fallen
further after MW2 and is now at -5.8.
90 day value is -0.3 ( 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 increased marginally after MW2 and
latest value is 0.1 .
( ONI of -0.5 to 0.5 is neutral. Above 0.5 is
El Nino, and below -0.5 is La Nina).
Indicator: ENSO Neutral (should be watched for El Nino development in August/September).
4. The Bay had hosted a pre-monsoon low
during mid April.
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 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 as a trough, through the peninsula, from Madhya Maharashtra towards
Kerala. It is giving adequate precipitation in the peninsular regions.
Outbreaks of pre- monsoon thunder showers which are expected normally in the
southern states and South Maharashtra, are taking place.
Thunderstorm activity in Southern Tibet is seen to be picking
up.
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 weak south-easterly, south of
8 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 late April, westerly jet
core was located between Lat. 21°N & Lat. 26°N with the wind speed varying
from 65 - 100 kts around 200 hPa. The highest wind speed of 100 kts was
recorded over Lucknow at 292 hPa on 26th April.
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
|
MW-2
|
MW-3 (1)
|
1) Cross Eq.Winds
|
Normal
|
Normal
|
-ve
|
2) Seasonal Low
|
-ve
|
Normal
|
-ve
|
3) ENSO
|
Neutral
|
Neutral
|
Neutral
|
4) Bay Low
|
-ve
|
-ve
|
-ve
|
5) ITCZ
|
Normal
|
Normal
|
Normal
|
6) Jet Streams
|
-
|
-
|
Normal
|
Overall
|
Slightly -ve
|
Normal
|
-ve
|
*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 then (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.
Special Thanks to Vagarian Rohit Aroskar for his contribution to this article.
