The second consecutive depression over the Bay of Bengal off the Odisha and West Bengal coasts has intensified into a deep depression, ranked next only to a cyclone in intensity, and lays centred on Friday noon about 200 km to the South-South-East of Balasore (Odisha); 140 km East-South-East of Digha (West Bengal); 100 km South-East of Sagar Islands (West Bengal); and 120 km South-South-East of Canning (West Bengal) 

Sea-surface temperatures are at around 29 °C around the North-West Bay where the depression is located currently. It was just about suitable for system development on Friday. Surprisingly, wind shear (the sudden change in winds speed and direction with height) values are very low at 9-18 km/hr. Typically, wind shear is high during a monsoon, which lops off the top of the storm tower, which is why cyclones do not normally develop during the season.

Rare deep depression

Given this context, even deep depressions are rare during a monsoon. In the instant case, close proximity to land may also have acted against the prospects of further intensification since a storm thrives on direct moisture feed from the sea. On Thursday, the parent low-pressure area had crossed into North-West Bay on to intensify as a depression on Friday morning, after gathering steam over North-East and adjoining areas of East-Central Bay, Bangladesh and Myanmar.

Follow-up circulation?

An extended numerical model outlook suggests that a cyclonic circulation may form over the Head Bay on the trail of the current deep depression, and is likely penetrate into Jharkhand, Bihar and Uttar Pradesh before heading back to Bihar by the end of the month (August). If this were to prove true, these areas (Bihar, Jharkhand and Uttar Pradesh) would set themselves up for another spell, following gains that some of them may make from the current deep depression.

Heavy rain forecast

Rainfall is forecast at most places over North Chhattisgarh and East Madhya Pradesh with heavy to very heavy rainfall at a few places and extremely heavy rainfall at isolated places. Rainfall is likely at most places over North-West Odisha, Jharkhand and Vidarbha with heavy to very heavy rainfall at a few places. Rainfall is predicted also over the remaining parts of Odisha, South Chhattisgarh and West Madhya Pradesh with heavy rainfall at isolated places.