Bureau of Meteorology (BOM) Australia ‘Outlook’ has been shifted to El Nino ‘ALERT’. This indicates increased chances of El Nino event forming this year. This also equates to approximately three times the normal chance of an El Nino forming. El Nino is an ocean-atmosphere coupled phenomenon. While the ocean was leading the way by adequate sea surface warming, atmosphere was bit reluctant . Now, the atmospheric indicators such as Southern Oscillation Index (SOI) have shifted towards El Nino threshold. However, the wind, clouds and broad scale pressure pattern indicate that ocean and atmosphere have yet to sync completely. Typical ocean-atmosphere reinforcement, as is normally seen during strong El Nino event , lacks bonding.
ENSO: Central and eastern Pacific sea surface temperatures (SST’s) have sweltered way beyond to El Nino threshold. The majority of models are predicting the likelihood of further warming. All the Nino indices are forecasted to remain well above the threshold mark right till the fall of the year.
Across the equatorial Pacific Ocean, there is clear spike in all the Nino indices, more so for the ONI (Oceanic Nino Index). Nino 3.4 index has shot up to 0.8°C from its last week threshold value of 0.4°C. After cessation of triple dip La Nina, this is the first time when all the Nino indices are over and above the threshold mark of 0.5°C.
IOD : The Indian Ocean Dipole is currently in neutral phase. The IOD index value for the week ending 04June 2023 was +0.32°C which is within neutral bounds (between -0.4°C and +0.4°C). This is the highest +ve value in the last 10 weeks. IOD need to grow sufficiently high to counter influence of Pacific warming. Weak IOD can exacerbate El Nino’s drying effect impacting southwest monsoon rainfall over Indian sub-continent. The occurrence of consecutive +ve IOD or -ve IOD is not very common. Also +ve IOD evolving together with La Nina and -ve IOD event working in tandem with El Nino is rare. Strong +ve IOD can weaken the ill effects of El Nino. +VE IOD did save the monsoon from the clutches of El Nino in 1997 & 2019.
MJO: Since late May, the enhanced phase of MJO has propagated from the Western Pacific into the Western Hemisphere. MJO will now get positioned over the Indian Ocean in phase 2&3 during the 2nd week of June and later to the Maritime Continent in phase 4 during 3rd week of June with truncated amplitude. Indian Seas, South China Sea and Philippines Sea are likely to become active basin during 2nd and 3rd week of June. Arabian Sea is hosting a Very Severe Cyclonic Storm Biparjoy and Philippines Sea anchoring Cat-2 equivalent hurricane Guchol. Another tropical storm is emerging in South China Sea , albeit with short sea travel. Increased typhoon activity over Western Pacific does not augur well for the Indian monsoon. While the tropical storm Biparjoy will head for northwest Arabian Sea, Bay of Bengal is likely to become active in the 3rd week of June. This may result an uptick in the intensity and progress of the southwest monsoon.
Eruption of El Nino has cascade of global impacts. Most mysterious of these is its potential influence on the Atlantic and Pacific hurricane season. Atlantic hurricane season tend to be less active during El Nino while the West Pacific often get accentuated. Increased typhoon activity of West Pacific is inversely related with Indian monsoon performance on account of sapping of moisture laden stream. Rainfall in the first 9 days of June has a shortfall of huge 60%.
