A point by point review of vagaries' August forecast showed a 65-70% accuracy in the overall sequences of meteorological events and happenings in the month.
City wise figures have varied a bit with the overall prediction (of all cities combined) overshooting by 24%.(See Current Page for break up).
Come September !
One of the most dicey and difficult months to predict as far as the SWM is concerned. We have the "uncertainty" of the withdrawal, and we could have a WD unwantingly interfering with the systems and interacting with the Easterlies in the North, or we could even have a stubbornly active axis refusing to move down.
But, lets see and analyse what could be the scene this year. This year we have seen the Monsoon "yo-yo" up and down, from a scary drought situation when all and sundry joined the bandwagon in blaming everyone from the met dept to the Govt. Then suddenly, August picked up with 2 lows and an UAC from the Bay, creating an active axis and an unusually active eastern off shore trough.
Now, September sees 1) A Neutral ENSO scenario. 2) A Neutral IOD position. 3) Below normal SST in the Arabian Sea, with Somali coast reaching 19c. 4) Strong Equatorial SW winds. 5) 200 hpa jet streams now Westerlies at 30N. 5) Western end of axis weakening slightly. 6) Siberian Tibetan pressure at 1012 today.
Points no 1) and 2) are not going to interfere this month with the normal flow. Point no.3) for forming coastal clouding along the west coast and 4) will favour that. 5) are just about normally placed, ready to move south at the call, which the weak low in Sindh is ready to give.
But, a stream of pulses, read lows, coming in from the Bay will keep the axis "alive" and prevent it from sliding in the first 10 days at least.
Sindh (Pakistan) regions have some hope of one more spell between 5th-10th of the month.
Hence, presuming the MJO gets into a weak phase around 10th, and does not allow any lows to form or the monsoon to activate, we can expect a withdrawal from the North Pakistan and Sindh region after the 10th. Maybe 10th-15th ? By the end of the month, the SWM would be out of all states north of Maharashtra and AP.
So, rainfall could be "maintained " in the first half of the month in the Central (SE Rajasthan, MP, Gujarat) and Northern Peninsula regions. The NW region and Northern plains can have thundershowers in the first half of the month.
Second half, sees more thunderstorm activities, precipitating heavy downpours in almost all of Central and Peninsula India. Rainfall starts shifting Southwards.
The rainfall for the Month would be near average. End of the season all India deficit may end up with a manageable -12%-15%
September Rainfall estimate for:
Mumbai: 425 mms (Avg). Outer Townships around Mumbai on Mainland around 550 mms.
Pune: 150 mms
Surat: 175 mms
New Delhi: 175 mms (Avg)
Bangalore: 200 mms
Chennai: 140 mms (Avg).
Estimates and Figures are worked out on basis of withdrawal and systems calculations. These are my personal calculations and may not be used for any commercial use.
Latest Monsoon Analysis from GSB on Inter Active Page..Must see