UPDATE on 18th July 2016:-
As noted in the above article under the caption "Places of Rainfall", one can see that rainfall occurred as per the astrological prediction.
Point no 1 in that says,
// (1) Conjunction of Mercury, Venus and Sun occurring in Cancer with closeness between Mercury and Venus happening:- Cancer being the sign of North, the North Indian lands - to the north of Vindhyas upto Himalayan foot hills will receive good rains.//
Right from the time the closeness of Mercury- Venus started, rainfall pattern occurred in the above mentioned places. Madhya Pradesh, particularly Satna in the Vindhyas region suffered flooding.
//(2) Jupiter in Jala nadi in Purva Phalguni :- Kosala, Kalinga (Oddisha), Vanga, Upavanga, Jatharanga, Vidharba, Vatsa, Andhra, Cedi, countries in and around the Vindhya mountains, Kishkindha, Nishada, Sabara etc will receive good rains.//
These places were the ones covered by SW monsoon so far.
// (3) Mercury crossing Venus on 16th and 17th July indicating formation of a system / cyclone or spurt in rainfall – the location is Pushya star which indicates eastern section of India. This means the impact will be on the east coast and eastern countries like Vrishaba, Chandrapura, Karvata, Maghada, (Bihar?) far-east Jyothisha (Bengal and Bangladesh?). This also means the formation of the system could be in the Bay of Bengal.//
Heavy rains accompanied with floods reported in Assam and Bihar.
Report here:- http://indianexpress.com/article/india/india-news-india/assam-rain-floods-throw-normal-life-out-of-gear-across-various-states-2944268/
These regions come under the regions mentioned above in the article.
As far as Chennai is concerned, there was cloudiness and / or mild rains in the days mentioned in the Garbottam chart. On 30th July (today) it must have been wet throughout the day as per the Garbottam of the related day in January. But it was cloudy today right from sunrise and it rained at night around 8 PM.
One insight from this is that what was observed as Garbottam was right, but its ability to give rains must have depended on 3/5 features whereas in the notings so far, only 2/5 features were present.
Another insight is that the Garbottam had lasted for 10 minutes to half an hour in most cases. Accordingly this reduces the chance of rainfall. Only when the garbottam has lasted long for more than an hour, it could have an impact.
Yet another feature is that presently Saturn in retrogression in Anusha star which causes shattering away of clouds by winds. That is what is exactly happening in Chennai. But the same seems to cause stormy showers in other places in TN and Bangalore where the rainfall is unleashed with the accompaniment of winds. Perhaps the Garbottam in those places were stronger than in Chennai.
The presently occurring ativrishti yoga of (1) closeness of Venus and Mercury (2) Venus and Mercury in the western sky (3) Sun, Saturn and Mars and watery signs etc are good for good rains in North India in particular (watery signs indicate North) and the places mentioned in the above article.