Tropical Storms

Types of tropical storms

Now, when it comes to tropical storms, you have probably heard different terms. That would be correct..."huh"?! Well, don't fret; the explanation is actually very simple: all those terms are correct. There is no difference between them other than their location.

Tropical storms form at different times of the year, depending on their location.

Global distribution of tropical storms

The global distribution, formation and development of tropical storms are related to global atmospheric circulation. The transportation of heat from tropical to polar latitudes is necessary, and the global atmospheric circulation is a global wind system providing that transportation.

Tropical storms occur in, you've guessed it, the tropics, in particular where the so-called intertropical convergence zone (ITCZ) is situated, where the northeast and southeast trade winds converge - roughly north of the Tropic of Capricorn and south of the Tropic of Cancer.

Most often, tropical storms form between 5^o and 30^o north and south of the Equator, i.e. low latitudes. Tropical storms most commonly occur in the warmest seasons, between summer and autumn. Furthermore, tropical storms need ocean temperatures of at least 27^oC and a water depth of about 197-230 ft/60-70m to form a storm.

As you can see, tropical storms form under specific conditions. Tropical storms cannot develop along the Equator because the Coriolis effect is not strong enough here, which is needed for tropical storms to spin. Read more on the formation of tropical storms below.

For more in-depth information, read our explanation of global atmospheric circulation.

Formation of tropical storms

Now that you know what tropical storms are, let's look at their formation, which happens in a specific sequence.

When solar heating causes the ocean's surface temperature to increase to at least 27^oC, the low-pressure conditions cause the warm air to rise, creating strong winds. Around a calm central eye of the storm, which can measure up to 30 mi/48 km across, the air spins upwards because of the Coriolis effect. As the warm air rises, it cools, and the water vapours condense to form cumulonimbus clouds, causing massive rainfall. When the air cools, the heat given off powers the storm. Cold air sinks, so when the air cools, it falls into the eye of the storm. That is why the eye of the storm has no clouds; it is drier and much calmer. The prevailing winds cause the storm to travel across the ocean, potentially making landfall at some point.

Effects of tropical storms

Because tropical storms are so powerful, they almost always leave a path of destruction, especially when they are near or travel over land. Between 2001 and 2010, over 500 tropical storm disasters killed nearly 170,000 people, affected more than 250 million people and caused estimated damages at US$380 billion!

There are primary and secondary effects, which can differ per location.

Tropical storms and climate change

It should not come as a surprise that climate change also affects tropical storms, with the potential of tropical storms happening in more and different locations. An effect of climate change is the warming up of oceans. Warmer oceans can allow storms to extend further north and south of the Equator, causing bigger storms and putting more habitable land areas and people at risk. Low-lying coasts, where many people live, are more at risk than ever before.

Regardless of an increase or decrease in the number of tropical storms happening, they will most likely increase in intensity, causing more damage and potential loss of life. Another effect of climate change is rising sea levels. This will make storms more destructive and increase coastal flooding.

Examples of tropical storms

With an average of 80-100 tropical storms per year, it is no surprise to learn there have been many devastating storms over many years. Let's look at a few examples.

Cyclone Bhola

The 1970 Bhola Cyclone occurred in East Pakistan (present-day Bangladesh) on 11 November 1970. The storm formed over the central Bay of Bengal on 8 November, from where it travelled north, gaining strength. On 10 November, the storm reached winds speeds peaking at 115 mph/185 km/h before making landfall on East Pakistan's coast. The following storm surge destroyed many offshore islands, wiping out entire villages and destroying crops. The storm eventually dissipated on 13 November.

The Pakistani government, then led by Junta leader General Yahya Khan, was heavily criticised as relief operations were delayed.

The Bhola Cyclone went down in history as the deadliest tropical cyclone ever recorded and one of the deadliest natural disasters in the world. At least 300,000 and possibly as many as 500,000 people lost their lives.

Fig. 4 - Weather satellite image showing Cyclone Bhola at the Bay of Bengal on 12 November 1970

Typhoon Nina

Typhoon Nina formed on 30 July 1975 and gained strength as it moved west. Peak intensity was reached on 2 August, and on 3 August, it hit Taiwan. As the storm moved to China's southeastern shore, it weakened slightly. That said, it wreaked havoc in this region! The storm moved through central China at a slow pace with massive rainfall. This caused many dams to collapse, such as the Banqiao dam, causing the third-deadliest flood in history, affecting over 10 million people. At least 229,000 people died. Material damages were estimated at US$1.2 billion.

Fig. 5 - Map showing the path of Typhoon Nina

Hurricane Sandy

On 22 October 2012, south of Jamaica in the western Caribbean Sea, Sandy developed as a tropical wave, where it quickly gained strength and was upgraded to a tropical storm a mere six hours later. On 24 October, the eye of the storm began to develop and later that day, the National Hurricane Center (NHC) upgraded the storm to a hurricane. In the evening of the same day, Hurricane Sandy, with winds of about 85 mph/105 km/h, made its first landfall near Kingston. When Sandy made its second landfall west of Santiago de Cuba on 25 October, the storm intensified into a Category 3 hurricane. Over the next few days, Sandy fluctuated between being a Tropical Storm, a Category 1 hurricane and a Category 2 hurricane before dissipating on 2 November. Sandy left a trail of destruction, with 233 people killed and material costs estimated at US$68.7 billion.

Fig. 6 - Map showing the path of Hurricane Sandy

Now that you know more about tropical storms learn more about managing them in our explanation on tropical storm management. If you want more case studies, read our explanations on Hurricane Katrina, Cyclone Nargis and Typhoon Haiyan.