What happens in January and why in December has the NEM remained Weak and WD somewhat Active ?
To prepare an answer to this, I will link up the ENSO situation first.
The ENSO situation remains neutral - neither El Niño nor La Niña. The past 30-45 days have remained and showed a neutral situation.
The SOI, has also shown neutral trends, with the current reading at -6.5.
A negative SOI trend generally shows weaker NEM pulses. The general trend is that SOI will remain negative, or maybe drop a few points more towards the negative next 15 days.
The Westerlies at 850 hp, have gained in the Southern region below India, and are seen pushing westwards into Sri Lanka since the last 15 days.("A" in Diagram) The MJO has remained weak as a result. The consequence was that it has forcefully resisted and blocked the developmemts of any meaningfull systems in the Bay and even any coming from the East. MJO now shows signs of strengthening in the Southern Hemisphere in the Australian (North) regions.( "C" in Diagram) .
The active MJO in the SE Asian regions moves more to the East into the Indonesia regions next 15 days.
A weak MJO envelops the Bay ("D" in Diagram)..
That means, the trough shifts further southwards towards the Australian continent. The Australian region may see more cyclones next 30-45 days, at least 2/3 major ones.
That will hasten up and withdraw the NEM in the next 8-10 days.
Now, if there is no meaningful activity in the Bay, gives a free hand to the WDs up North. The Eastward bound systems are "allowed" to move thru Northern India and need not get pushed up towards the extreme North.
The 200 hp jet streams are getting pushed more to the North, and will prevail above the 30N line areas ("B" in Diagram).
Seeing the situation next 30 days, I would expect around 3 major and 3 minor WDs in January to cross the Northern regions of the Sub-Continent.