The 1991 North Indian Ocean Cyclone season was the period in which tropical cyclones formed to the north of the equator in the Indian ocean. During the season tropical cyclones were monitored by the India Meteorological Department (IMD) and the Joint Typhoon Warning Center. The IMD assigned all depressions that it monitored with BOB followed by a number in numerical order. The JTWC also assigned a number and either the letter A or B depending on where the depression was when the first advisory was issued.
During the year there were eight depressions that were monitored by the IMD while the JTWC monitored four during the year of which one was not monitored by the IMD. The first cyclone of the year formed on January 17 and had little effect on ships that were moving through the Arabian sea to take part in the Gulf War. The deadliest cyclone during the year was Super Cyclonic Storm BOB 01 which killed over 138,000 people.
During January 14, the JTWC started to monitor an area of convection that had developed within the near equatorial trough of low pressure, about 900 km (560 mi) to the southeast of Colombo, Sri Lanka. Over the next couple of days the disturbance moved towards the northwest under the subtropical ridge of pressure, before early on January 17, the JTWC noticed a steady increase in deep convection and issued a tropical cyclone formation alert. Later that day the JTWC initiated advisories as the disturbance had intensified into a tropical storm and designated it as Cyclone 01A. As the Cyclone was suffering from being in an area of strong vertical wind shear it was not able to intensify past minimal tropical storm strength of 65 km/h, (40 mph). During the next couple of days, strong upper level winds stripped deep convection away from the center with the JTWC downgrading the cyclone to a tropical depression early on January 19. The remaining low level circulation center slowly dissipated with the JTWC issuing their final advisory early the next day.
The cyclone posed a direct threat to allied forces, which were operating in the Arabian Sea, Persian Gulf and the Red Sea, in the build up to the Gulf war. However it was not a significant factor in the build up to the Gulf war and due to it low latitude track and weak intensity it had little effect on ships steaming to the Middle East. As a result of the cyclone remaining out to sea there was no reported impact to land.
Cyclone Two hit Bangladesh on April 29 as a strong cyclone. It brought a tremendous storm surge and massive wind damage, resulting in the deaths of over 138,000 people. Cyclone 2B was the deadliest cyclone on Earth since the 1970 Bhola Cyclone. It also destroyed an estimated 1 million homes, leaving as many as 10 million people (a substantial portion of the country's population) homeless.
On May 30, exactly a month after the previous storm, a tropical storm formed in the Bay of Bengal. It moved north-northeastward and strengthened to a 60 mph tropical storm on June 2, shortly before it hit nearly the same place as 02B did in the Bangladesh region. It dissipated the next day, only to disrupt relief efforts. Fortunately, it caused no reported fatalities due to the well-executed warnings.
Early on August 22, reported that Depression BOB 04 had formed about 160 km (100 mi), to the southeast of Balasore, India. As the depression moved towards northwest, it failed to intensify any further. The depression made landfall in the Indian state of Orissa later that day and maintained its identity until it weakened into a low pressure area early on August 26. The depression's windspeeds were estimated to have peaked at 45 km/h (30 mph), whilst the lowest pressure recorded was 992 hPa.
The final storm of the season, which formed in the eastern Bay of Bengal on November 9, hit eastern India as a 45 mph tropical storm on the 15th. It dissipated the next day over the country.
The Cyclonic storm brought torrential rain and flash floods across southern India when it made landfall. Twenty-four hour rainfall totaled 480 millimetres (19 in) at Karaikal. As a direct result of the flooding at least 40 people died.
^Darwin Regional Specialised Meteorological Centre (1991). "January 1991". Darwin Tropical Diagnostic Statement (Australian Bureau of Meteorology) 10 (1): 4. ISSN1321-4233. Archived from the original on August 26, 2012. Retrieved August 26, 2012.