Where and When Do Tropical Storms Occur?

🗺️ Where and When Do Tropical Storms Occur?

Tropical storms are not random. They form in specific ocean basins, during specific seasons, and within a defined latitude band. Understanding their distribution requires understanding the conditions they need — and where those conditions simultaneously exist.

The Latitude Belt: 5°–20° North and South

Tropical storms form between roughly 5° and 20° latitude in both hemispheres. This band is calibrated by two competing requirements that must both be met:

• Must be close enough to the tropics — so ocean surface temperatures exceed 26°C, providing the thermal energy to drive evaporation and convection. Beyond about 20° latitude, the ocean is typically too cool for storm formation
• Must be far enough from the equator — so the Coriolis effect is strong enough to impart rotation to the inward-flowing air. At the equator (0°), the Coriolis effect is zero: air rushing toward low pressure goes straight inward without rotating, and no organised storm structure develops

The 5°–20° belt is where both conditions are simultaneously met. It encircles the globe across all tropical ocean basins.

The Main Ocean Basins

Region	Local Name	Season (Peak)	Notable Examples
North Atlantic / Caribbean	Hurricane	June–November (September peak)	Katrina 2005, Harvey 2017, Dorian 2019
Western North Pacific	Typhoon	June–December (August–October peak)	Haiyan 2013, Hagibis 2019
North Indian Ocean / Bay of Bengal	Cyclone	October–December and April–June	Nargis 2008 (Myanmar), Amphan 2020
Southern Hemisphere (Indian Ocean / SW Pacific)	Cyclone	November–April	Winston 2016 (Fiji), Idai 2019 (Mozambique)

Note that all three names — hurricane, typhoon, cyclone — describe exactly the same type of storm. The difference is purely geographical: where the storm forms determines what it is called. For examiners, using the wrong name for the correct ocean basin is a common error; avoid it.

Storm Track — How Tropical Storms Move

Tropical storms follow a characteristic curved track driven by global wind patterns. Understanding this track explains which coastlines face regular storm threats:

• Initial westward movement: Tropical storms are steered by the trade winds, which blow east-to-west across the tropics. Storms initially move westward, toward eastern coasts of land masses (e.g. the Philippines, eastern USA coastline, Caribbean islands)
• Poleward recurvature: As storms move into higher latitudes (above about 20°), they are increasingly influenced by mid-latitude westerlies and tend to curve poleward and then eastward, eventually departing the tropics
• Weakening phase: As they recurve into cooler waters and higher latitudes, they lose tropical characteristics. They either dissipate or transition into mid-latitude (extratropical) storms — which can still deliver destructive winds and rainfall to temperate regions including the UK

Climate Change and Tropical Storms

As global ocean temperatures rise due to climate change, the conditions for tropical storm formation are expanding. Current evidence suggests the nature of storms is shifting:

• The intensity of the strongest storms is increasing — a higher proportion are reaching Category 4 and 5 intensity
• Storms are intensifying more rapidly — giving forecasters and communities less warning time before major landfalls
• Storms are forming at higher latitudes than before, affecting areas previously outside the storm belt
• Storms are moving more slowly in some regions, dropping extreme amounts of rainfall in one location (as Hurricane Harvey did over Houston in 2017, dropping over 1,500 mm of rain in four days)