An early take on our Summer Monsoon 2019

-

The buzz is back as the monsoon 2019 season nears. Already a bunch of predictions are pouring over the internet, so here's one more to add to the reader's confusion! :). 

***********************
MY PREDICTIONS   (Unofficial):
***********************

TIMELY ONSET OF MONSOON (since ENSO generally doesn't impact the onset) - 

Hits Kerala on June 1st (+ 2 days). 

Mumbai ~ June 11th (+2 days).


1. MUMBAI, GOA, & KOKAN COAST - NORMAL/SLIGHT EXCESS

2. KERALA  & PENINSULAR INDIA - SLIGHTLY BELOW NORMAL

3. CENTRAL INDIA, MARATHWADA, VIDARBHA - BELOW NORMAL

4. EAST COAST -  SLIGHTLY BELOW NORMAL

5. NORTH-EAST - NORMAL

6. GUJARAT, KUTCH, NORTH WEST - BELOW NORMAL

7. NORTH INDIA - NORMAL

8. SOUTH INDIA (INTERIOR TN, INTERIOR KARNATAKA, & AP) - BELOW NORMAL

****OVERALL SWM 2019 - BELOW NORMAL (92-95% of LPA)****


OVERARCHING CONCLUSIONS:

1. Interior Karnataka, Andhra, Marathwada & Vidarbha regions need to exercise caution, since these regions have been hit by intermittent droughts since 2014.

2. Drier than normal June and probably a wetter August.

*************
ANALYSIS 
*************

I am going to keep it simple. Three things matter:

1. ENSO STATUS: Still in "ALERT" mode, means it has not fully developed. Easterly trade winds (that bring moisture from the Pacific to the Indian sub-continent) have weakened to some extent, but an entire reversal hasn't happened, which is a primary precursor of a full-blown ElNino. Moreover, the sea surface temperature (SST) is only marginally higher.

Therefore, I tag the present situation as a weak ENSO, which is a problem in itself as it is associated with a high inter-annual variability in R/F.

 (What is the meaning of high inter-annual variability: For e.g., a fully matured ENSO season is almost always associated with below normal R/F, but for a weak ENSO season, other local factors in the Indian Ocean play a key role, which may offset the ENSO effect and hence becomes pretty hard to predict).

2. INDIAN OCEAN DYNAMICS (IO): This is another tough one - because....the Indian Ocean Dipole doesn't have a well-defined structure as the ENSO. In any case, there is evidence of warm and cold pools in the western and eastern Indian Ocean basins respectively. The lingering question is - how strong is this coupling? It will decide the moisture incursion from the West (i.e. Arabian Sea). For now, I am going to say that it is neutral - meaning neither strong nor weak.

3. EQUATORIAL DYNAMICS: Convection cell or the famous Intertropical Convergence Zone (ITCZ trough) has moved close to EQ and is moving upward, which is a necessary criteria for our Summer monsoon. The trough (low pressure ITCZ) needs to come close to 20-25 deg N and the tropical ridge (the high pressure zone) needs to move above it. The wind patterns are indicative of this movement and it is happening as expected. This means chances of MJO moving into our basin during the monsoon 2019 season is high. 

So, as of now, in my opinion, the complete scenario looks like:

 1. Weak ENSO - Negative contributor to R/F.

 2. Near neutral IO dynamics - Neutral effect.

 3. MJO currents seem to be moving into our basin - Positive contributor to R/F. Is it going to be enough to offset #1?

 ***The X-Factor - How much moisture incursion due to an active convection (i.e. in layman terms MJO strength) occurs over the Indian subcontinent?

 ***The X-Factor in my opinion is going to decide the fate of our SWM 2019. Clarity on the X-factor around end of May 2019 (closer to the onset).


Note: Another blog will be posted after the onset on monsoon, to provide corrections based on the incumbent meteorological conditions.
You can follow my twitter handle @SriGMFL

Disclaimer: The content given here are all personal views and the author will not be held responsible or held liable for any oversight or misinterpretation.

Comments

Post a Comment

Popular posts from this blog

Onset of Indian summer monsoon

-
Image
The onset of Indian summer monsoon (or southwest monsoon) is the most anticipated event for the Indian population. The first monsoon shower is the most awaited one as many seek respite from the scorching heat, little ones gleefully wanting to play in the cool showers, and the agricultural community get in full swing to prepare the land for farming. Over the past few years, owing to climate change, the onset has been delayed ( https://www.firstpost.com/economy/imd-forecasts-delay-in-onset-of-monsoon-may-hit-kerala-coast-around-5-june-1971211.html ) and the monsoon itself has been erratic, with brief periods of heavy rain (active phase) and periods of no rain (break phase). This is in contrast to a decade or two back, when the onset on monsoon would be well-timed and the nature of monsoon was also steady (with consistent rains through out the season). However, urbanisation, greenhouse pollution, deforestation, and many other anthropogenic activities have led to the late onset and incon...
Read more

Indian Summer Monsoon 2018

-
Image
  A few days back, both Skymet weather services (a private weather forecasting firm) and the Indian Meteorological Department (IMD, a government organization) gave their predictions for the Indian summer monsoon 2018. Overall, they painted a positive picture, where both confirmed that monsoon 2018 is likely to remain normal at 100% (with error margin of +/-5%) of the long period average (LPA), where the nationwide LPA stands at 887 mm for the four-month period from June to September (for more details on this prediction see https://www.skymetweather.com/content/tag/monsoon-2018/ ). To elaborate, >105% of LPA indicates excess rainfall, <95% of LPA indicates below normal rainfall, and <90% of LPA indicates drought. Their prediction is based on the nationwide average and hence does not account for the state- and region-wise variabilities. Hence, although the prediction for 2018 is ‘normal rainfall’, this does not exclude the possibility of excessive rainfall in some regio...
Read more

Cyclone ASANI

-
Image
Our team has been on the fence with regards to the SEVERE CYCLONIC STORM (SCS) ' ASANI' , since the ridge dynamics were highly tricky. The cone of uncertainty surrounding this cyclone is quite huge, with still some divergence in the weather models as to its exact track, landfall location, as well as intensity. This uncertainty is very uncommon given that the cyclone is just 48 hours within possible landfall. However, as an upcoming (read startup) private player in the field of weather and climate services, it is important to spell out what we feel is likely to happen based on the dynamics that we interpret. The Cyclone has enough fuel to maintain Cyclonic Storm status. The vertical wind shear is the only unfavourable factor, but it is not too high. The ridge action has been the main X-factor. The Indo-Pacific ridge movement has been very unstable for past few days and hence the models were divergent on the track. But now, it looks like the Indo-Pacific ridge has moved closer to...
Read more