The increased risk of an El Niño occurring this year is twice the usual chance, according to experts. While all international climate models predict that tropical Pacific Ocean temperatures will reach El Niño thresholds during the southern hemisphere winter, an atmospheric response is also necessary for an official El Niño declaration.
Currently, the Nino Index 3.4 is trending close to 0.9 to +1°C, indicating the robust transition of the Nino Region into El Niño in the upcoming months. The Indian Ocean Diapole Index is also trending close to +0.7, expected to reach +1.3 as a positive IOD in the next JJA (June/July/August) season.
With the current SST in the East Pacific Waters boiling and the Indian Ocean Index close to +1.0, it suggests that the PIO Transition has taken place, potentially leading to an enhanced severe cyclone in the Arabian Sea.
Evolving years from La Niña to El Niño are usually marked by sinking cells over the Indian Ocean, which can result in more shear factor dominating the Bay of Bengal and deficient monsoon rains in core central India. Currently, the evolving positive IOD is likely to be a key factor influencing rainfall activity, leading to normal to excess rainfall in the West coast and below-normal rainfall in central India plains.
The Arabian Sea waters are boiling up to 30 to 31°C, while the Bay waters are boiling around 29 to 30°C. These favorable conditions indicate that the West coast can expect more rains.
The Somali Jet Index, which measures the speed of the Somali jet, shows that the monsoon momentum has not yet reached the West coast mainland, as per the current graph.
South West Monsoon 2023 - What we can Expect
The guidelines to be followed for declaring the onset of monsoon over Kerala and its further advance over the country are enlisted below:
a) Rainfall
If after 10th May, 60% of the available 14 stations enlisted*, viz. Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu and Mangalore report rainfall of 2.5 mm or more for two consecutive days, the onset over Kerala be declared on the 2nd day, provided the following criteria are also in concurrence.
b) Wind field
Depth of westerlies should be maintained upto 600 hPa, in the box equator to Lat. 10ºN and Long. 55ºE to 80ºE. The zonal wind speed over the area bounded by Lat. 5-10ºN, Long. 70-80ºE should be of the order of 15 – 20 Kts. at 925 hPa. The source of data can be RSMC wind analysis/satellite derived winds.
c) Outgoing Longwave Radiation (OLR)
INSAT derived OLR value should be below 200 wm-2 in the box confined by Lat. 5-10ºN and Long. 70-75ºE.
Northern Limit of Monsoon (NLM)
Invest 92A in Arabian is concentrated in to Depression.Current wind 30kt with 1002Mb Central Pressure lying in 9N Lat.Favourable SST will fuel the systems in to a strong system category.Monsoon winds will align towards Kerala coast & onset expected within Next 32 hrs.
June - 2023
In June 2023, the onset of the South West Monsoon in Kerala is expected around the 7th or 8th, accompanied by a strong surge associated with a vortex formed in the Arabian Sea. Due to favorable SST conditions, the system may become stronger and move towards the central Arabian Sea, influencing a fast monsoon onset up to the Konkan region.
September - 2023
Normal to excess rainfall is anticipated in Kerala, Karnataka, Tamil Nadu, Telangana, Andhra Pradesh, Maharashtra, Madhya Pradesh, and Odisha. However, below-normal rainfall is expected in North and Central West India.
The anomaly chart illustrates excess heavy rains in Kerala, Karnataka, Tamil Nadu, Andhra Pradesh, and Telangana. Rains are expected to decrease significantly in most states, with close to normal rainfall expected in West Bengal and South Tamil Nadu. There are signs of a system potentially forming in the Bay of Bengal, moving towards Myanmar, Bangladesh, or close to West Bengal.
In conclusion, Kerala, coastal Karnataka, including the Cauvery Basin, Maharashtra, and parts of Gujarat, Tamil Nadu, and Andhra Pradesh can anticipate close to excess rainfall. Telangana, Odisha, and Madhya Pradesh may experience normal to below-normal rainfall, while Central and North West India are likely to receive below-normal or deficient rains. These forecasts are based on monthly data from ECMWF and personal inference using tropical wave.As per my observation Upcoming monsoon rains wont coincide with 2018 flood rains.If any changes in future will update in advance.