Two successive timelines set by the India Meteorological Department (IMD) for the first pre-monsoon low-pressure area to form in the Bay of Bengal have elapsed, forcing it to extend the watch till this (Friday) evening.
The IMD had initially fixed the timeline for April 29, which was later revised to April 30. Normally, this is taken to mean the likely loss of confidence with respect to the forecast time and place of the event. In this case, a preparatory cyclonic circulation is hovering over South Andaman Sea and needs to build just the required mass to convert itself.
Competing pulls
One potential reason why it is not able to do just yet is the competing pull on the south-westerly flows it shares with a stronger circulation over the East Indian Ocean off Sumatra (Indonesia), and a couple of less intense ones lying over the Malacca Strait (off Malaysia) from where it had reached the South Andaman Sea.
The Sumatran circulation is attracting a bulk of the south-westerly flows that would normally have got directed into the South Andaman Sea. Some flows are taking a detour from here to feed into the Malacca Strait. The Sumatran circulation would have to blink first for the South Andaman Sea circulation to prosper and set up the low-pressure area.
Sea surface temperatures
On the other hand, the delay in genesis and a slight change in track into a warmer (sea surface temperatures closer to 30 degrees Celsius or above) into West-Central Bay of Bengal could, as a few models venture to suggest, intensify the system to near-cyclonic strength.
This is because it allows the system to gather strength as it shifts its base from the South-East and adjoining South Bay (sea-surface temperatures of 28-29 degrees Celsius) to the West-Central Bay (30-31 degrees Celsius). Warmer seas and longer stay of the circulation in the waters will just accord it the attributes it needs to intensify.
Deep depression likely
These models project that the storm (a deep depression, as indicated by the IMD and supported by the US Navy Global Environmental model) may inch closer to the Andhra Pradesh coast before veering to the opposite (North-North-East) towards Myanmar-Bangladesh. It would also enter the less warm seas of the North and North-East Bay of Bengal. The European Centre for Medium-Range Weather Forecast suggests that the system may reach even closer to Visakhapatnam by May 10 till when the forecast is currently available.