With the impending Cyclone Mocha dominating discussions over the past few days, cautionary, warning and danger signals that the Bangladesh Meteorological Department (BMD)asks ports to hoist have become a staple item of news.

As of Friday evening, maritime ports of Chattogram, Cox's Bazar, Mongla and Payra have been asked to hoist local warning Signal 4.

The following is a look at what each of the signal means, according to BMD:

Distant Cautionary Signal 1

There is a region of squally weather (wind speed of 61kmph) in the distant sea where a storm may form.

Distant Warning Signal 2

A storm (wind speed of 62-88kmph) has formed in the distant deep sea. Ships may face danger if they leave harbour.

Local Cautionary Signal 3

The port is threatened by squally weather (wind speed of 40-50 kmph).

Local Warning Signal 4

The port is threatened by a storm (wind speed of 51-61kmph) but it doesn't appear that the danger is as yet sufficiently great to justify extreme precautionary measures.

Danger Signal 5

The port will experience severe weather from a storm of slight or moderate intensity (wind speed of 62-88kmph) that is expected to cross the coast.

Danger Signal 6

The port will experience severe weather from a storm of slight or moderate intensity (wind speed of 62-88kmph) that is expected to cross the coast.

Danger Signal 7

The port will experience severe weather from a storm of light or moderate intensity (wind speed of 62-88kmph) that is expected to cross over or near the port.

Great Danger Signal 8

The port will experience severe weather from a storm of great intensity (wind speed of 89kmph or more) that is expected to cross the coast.

Great Danger Signal 9

The port will experience severe weather from a storm of great intensity (wind speed of 89kmph or more) that is expected to cross the coast.

Great Danger Signal 10

The port will experience severe weather from a storm of great intensity (wind speed of 89kmph or more) that is expected to cross over or near the port.

Failure of Communication 11

Communications with the Storm Warning Centre have broken down and local officers consider that a devastating cyclone is following.