b. On 1st September Mercury is crossing Jupiter by retrogression. This triggers rainfall. Mercury is crossing in Uttra Phalguni star which signifies countries of the South. This includes the regions of Eastern Ghats, Mahendra parva, Malaya parva (Kerala), catchment areas of Kavery, Vena (Pennai) etc, Ceylon, Kollam and western parts of Karnataka.
The Garbottam chart for Chennai was almost exact on realization of rainfall except on 2 days. They were Sep 8th and Sep 15th.
The corresponding Garbottam day for Sep 8th had moon conjunct with Rahu thereby indicating rainfall accompanied with thunder or storms. Surging clouds were witnessed on the evening of 8th but it did not rain. The plausible rationale is that the Garbottam features were not strong. My data shows that the corresponding day (March 1) had cloudy and cool breeze between 8 AM and 9 AM. This should have given rains, but a major planetary event was happening on 8th. Mercury was re-entering Leo backwards on that date. Usually, when it enters the next sign, it had triggered rainfall. But now it is entering the previous sign by backward motion, it had spoiled the rainfall! A spoiled rainfall / failed Grbottam must give plenty of rainfall in the next possible date. It happened on Sep 15th!
Ironically Sep 15th was not supposed to have rainfall due to solar eclipse on the corresponding date. But it rained on 15th. When I checked the data and the thithi etc I found that though Amavasya started at 10-34 AM on March 8th, solar eclipse started on the early morning of March 9th. Garbottam had happened on 8th March around 11-30 AM. This was soon after Amavasya began. This shows that Garbottam can give rains if eclipse was not running at that time. This also means that the entire day need not be rejected on account of eclipse. Only the exact timing matters. Moreover the deferred rainfall due to Mercury's re-entry into the previous sign had to give its due on this date as it is the next major Garbottam realization day.
The general rainfall scenario for this month of September followed the planetary predictions - but with an exception. From September 21st onwards, heavy rains lashed Andhra Pradesh and Telangana with Hyderabad receiving the century's highest rainfall for September during this period. Many areas were flooded with Mahanadi posing flood-threat.
Earlier in the article I have noted down the date - 17th September as the date capable of giving heavy rains. But the combination dissipated within 24 hours.
The heavy rainfall that started on 21st can be linked to the movement of Mercury. Mercury was in retrogression from August 30th onwards. It did rain on that date. Further on Mercury moved backwards and entered the previous sign Leo on September 8th - 9th. The re-entry failed to give rain to South India / Tamilnadu (Mercury in Uttara Phalguni) at that time. Mercury kept moving into the sign till 21st September. On that date it reached the limit of its retrogression and on 22nd it started the forward motion. These two dates were marked with heavy rains on the regions denoted by Purva Phalguni as Mercury was moving in that star. The regions coming under Purva Phalguni are those from Andhra Pradesh to Oddhisha, Kiskinda (North of Deccan plateau) South of Vindhya mountains. These regions received heavy rainfall on the dates starting from Mercury's turn around motion.
These rains will continue till 30th September as Mercury continues to be in Purva Phalguni until them. Thereafter it enters Uttara Phalguni. Uttara Phalguni indicates region south of Andhra, that is, Tamilnadu. On 3rd October, Mercury re-enters Virgo where it will be chasing Jupiter. Normally entry into a sign has come with rainfall. This time it is re-entry in the forward direction. This is likely to trigger rainfall as Garbottam chart for October for Chennai shows rainfall from October 4th onwards.
UPDATE on 29th September:
It rained well since 26th September in Chennai in my place and other parts of Chennai. The Garbottam chart shows rains on 25th September and not on dates after that. When I checked the data, I found that the Garbottam occurred on 17th March in Arudra star. Though the corresponding date is 25th September, the garbottam in Arudra can give rains for many days in the rainfall realisation date. As per rule if good Garbottam occurs in Arudra star in the month of Panguni, it would rain for 24 days in the realisation period.
Quoting from my first article in the current series on Rainfall observation (here):-
On March 16th and 17th when Moon was transiting Arudra there was cloudiness at night and day. Sun was hidden for most part and there was pleasant breeze. The result started in 26th September and is likely to continue for 24 days as per rule. The further Garbottam chart for October shows wetness on most days in October though the intensity of rains is not high on all days.
Another feature corresponding to the rainfall date is the forward transit of Mercury after retrogression in Purva phalguni star. Generally Purva Phalguni gives rains. Moon is also presently transiting the sign of Leo where Purva phalguni is located. All these combine to ensure wet climate.
As per IMD, SWM started retreating from 28th September onwards. In the article above I connected the retreat / withdrawal to the ending of Mercury- Venus closeness. It occurred on 12th September. But the actual retreat started on 28th September. When I checked the distances between Mercury and Venus, I found out a new revelation. Mercury and Venus were at their maximum gap of 48 degrees from 28th September onwards. This lasts till 5th October. From 6th October onwards, the gap is getting reduced gradually degree by degree. Therefore the learning is that monsoon retreat starts when these two planets reach the maximum distance between themselves.
On 27th October the closeness between Mercury and Venus begins thereby ushering in a rainfall period again which can be linked to NEM. On that date, Mercury is in deep conjunction with Sun and will be behind Venus by 7 degrees. This is perfect setting for good rainfall.
However my Garbottam chart for October shows that on the corresponding Garbottam date for 25th October - which was April 17th, , wind direction changed for the first time to south- south west. That means wind direction will be from North - North east from 25th October onwards. I am eager to check this onset of wind in October. The details will be posted shortly.