Where the Hurricane Season Peaks Twice

If you've followed tropical storms and hurricanes in the Atlantic Ocean over the years, you are probably familiar with the Atlantic hurricane season's single peak in activity that runs from August into early October. Those three months alone have accounted for 78 percent of the named storms over the course of a season since 1950. Several other ocean basins in the world, including the eastern Pacific and western Pacific, also have single peaks to their tropical cyclone seasons.

(Note: A tropical cyclone is what we refer to as a hurricane in the Atlantic Ocean.)

However, there is one spot in the world where the tropical cyclone season has two peaks. This location is the northern Indian Ocean, including the Bay of Bengal and Arabian Sea, which are separated by the Indian Peninsula. According to the National Oceanic Atmospheric Administration (NOAA), the first peak runs from April to June and the second from late September into early December. In summer months between these peaks, there is very little tropical cyclone activity. The India Meteorological Department says that even when one does form in those months, they tend to be weak monsoon depressions that move inland quickly with heavy rain.

So, what is the reason for this dual peak in the tropical cyclone season in the northern Indian Ocean?

It's all related to the Indian Monsoon. A monsoon is a seasonal wind shift and India is famous for having the most pronounced monsoon in the world. Southwest winds from the Indian Ocean feed moisture into the country from late spring through summer, fueling heavy rains at times. The other months of the year, winds are typically from the northwest off the dry continent.

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As the monsoon peaks during the summer, upper-level winds in the northern Indian Ocean become too brisk for strong tropical cyclones to develop. Instead, the aforementioned weak monsoon depressions can form at times.

It's typically right before the monsoon kicks in (April-June) and right after it fades (September-early December) that there is a window where upper-level winds relax enough for possible strong tropical cyclone development in the northern Indian Ocean. This results in the twin peaks in the tropical cyclone season (hurricane season) in this ocean basin.

Sadly, the Bay of Bengal and Arabian Sea have seen some of the deadliest tropical cyclones in the entire world during these twin seasons. In fact, one cyclone in November 1970 is estimated to have killed at least 300,000 in Bangladesh. Cyclone Nargis in May 2008 killed more than 130,000 in Myanmar. Most of the deaths in this region have been due to extreme storm surge flooding in coastal locations.

(MORE: The Storm that Killed 300,000)

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