Tropical Cyclones

“Hurricane”, “tropical cyclone,” “very severe cyclonic storm” and “typhoon” are different terms for different regions for the same phenomenon. They are weather phenomena accompanied by torrential rain and sustained wind speeds of more than 119 kilometres per hour:

• In the western North Atlantic, central and eastern North Pacific, Caribbean Sea and Gulf of Mexico, this weather phenomenon is called a “hurricane”
• In the western North Pacific, it is called a “typhoon”
• In the Bay of Bengal and Arabian Sea, it is called a “very severe cyclonic storm”
• In the western South Pacific and south-east Indian Ocean, it is called a “severe tropical cyclone”
• In the south-west Indian Ocean, it is called a “tropical cyclone".

Questions and Answers

When do tropical cyclones occur?

The typhoon season in the western North Pacific region typically occurs from May to November. The American/Caribbean hurricane season occurs from June to November, peaking in August and September. The tropical cyclone season in the South Pacific and Australia normally occurs from November to April. In the Bay of Bengal and Arabian Sea, tropical cyclones usually occur from April to June and from September to November. Tropical cyclones in the East Coast of Africa normally occur from November to April.

How are tropical cyclones classified?

They are classified into five categories of sustained wind speeds:
Category 1 – 119-152 km/h
Category 2 – 153-177 km/h
Category 3 – 178-209 km/h
Category 4 – 210-249 km/h
Category 5 – over 249 km/h

How is climate change impacting tropical cyclones?

The current opinion of international experts is that with climate change, the total number of tropical cyclones worldwide will likely either decrease or remain unchanged. However, a likely increase in tropical cyclone intensity means that the frequency of the strongest tropical cyclones will “more likely than not” (which means “probably” in scientific terms) increase.

How are tropical cyclones named?

Tropical cyclones can last for one week or more; thus there can be more than one cyclone at a time. Weather forecasters give each tropical cyclone a name to avoid confusion. Each year, tropical cyclones receive names. The name list is proposed by WMO Members of a specific region. Sometimes it is a woman’s name; sometimes a man’s. The names also include animals or flowers. The only time there is a change in the list is if a storm is so deadly or costly that the future use of its name for another storm would be inappropriate. This was the case with Hurricane Katrina (USA, 2005) and Typhoon Durian (Philippines, 2006).

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