A Traveler’s Guide to Civilian Tropical Cyclone Scales

As a vacationer or business traveler, you might run into stormy weather during tropical cyclone season.

While these natural hazards can happen almost any time, given the right conditions, they are most frequent from June through November in the northern hemisphere and from November through April in the southern hemisphere.

Outside your region, different names and intensity scales may be used for them. Let’s imagine a Category 3 storm is approaching, say, Miami, Florida. Just for the sake of argument, it’s not winter in the southern hemisphere and in Perth, Australia, they’re battening down the hatches as a Category 4 nears the coast.

Which storm is more dangerous?

Now don’t cheat and look at satellite images…
 

Top:  Category 3 Hurricane Sandy threatens Florida in 2012. Bottom:  Category 4 Billy off Australia's northwest coast in 2008.

Top: Category 3 Hurricane Sandy threatens Florida in 2012.
Bottom: Category 4 Tropical Cyclone Billy off Australia’s northwest coast in 2008.


To answer that question, we should first take a quick look at what a tropical cyclone is, as well as how these dangerous storms are monitored in various parts of the globe.

Tropical cyclones

Hurricane experts at the US National Oceanic and Atmospheric Administration say:

A tropical cyclone is the generic term for a … low-pressure system over tropical or sub-tropical waters with organized convection (i.e. thunderstorm activity) and definite cyclonic surface wind circulation.

It’s “tropical” because it runs off heat and moisture. Ideal spawning grounds are in the tropics, where water is at least 80 degrees F (26.5 degrees C) down to a depth of at least 150 feet.

“Cyclone” means the winds are blowing inward toward the central area of low pressure. Because of the Coriolis effect, they spiral in counterclockwise in the northern hemisphere, and clockwise in the southern hemisphere.

See the different “curls” on the two storms pictured above?
 

 

Monitoring tropical cyclones

Tropical cyclones are known as “hurricanes” in the Atlantic basin and northeast Pacific Ocean (east of the International Dateline); “typhoons” in the northwest Pacific west of the dateline; “cyclonic storms” in the northern Indian Ocean; and as the very straightforward “tropical cyclones” everywhere else.

The World Meteorological Organization has six Regional Specialized Meteorological Centers (RSMCs) and six Tropical Cyclone Warning Centers (TCWCs) to provide advisories and bulletins and gather up-to-date weather information.

Forecasters in these international centers use their own regional system when it’s time to inform the public about an approaching tropical system.

Regional centers and scales

Generally speaking, all international tropical cyclone categories were developed from the Beaufort Wind Scale. If you’ve ever encountered a term like “Force 10 gale” in a movie or a book (or in real life), that’s a reference to the Beaufort scale.
 

WMO Tropical Cyclone Centers.  Source

WMO Tropical Cyclone Centers. WMO

The famous Saffir-Simpson Hurricane Potential Damage Scale is used by the RSMC Miami-Hurricane Center/US National Hurricane Center for storms that form in the Atlantic and eastern North Pacific oceans as well as the Caribbean and Gulf of Mexico, and by the RSMC Honolulu/US Central Pacific Hurricane Center for the northern Pacific between the International Dateline and 140 degrees west longitude.

The Saffir-Simpson scale was developed by meteorologist Robert Simpson and civil engineer Herbert Saffir in 1969 and then tweaked a bit in 2010. Of special note is that it uses a sustained wind speed measured over one minute rather than the 10 minutes used everywhere else. This means that the same storm will show about 10% higher measured wind speeds in the US than in other parts of the world.

The northwestern Pacific Ocean and South China Sea are covered by the RSMC Tokyo-Typhoon Center/Japan Meteorological Agency. The Australian Bureau of Meteorology table duplicated at the bottom of this article shows how the scale used here and in the following regional centers compares to the Saffir-Simpson scale.

The RSMC New Delhi/India Meteorological Department monitors the Bay of Bengal and the Arabian Sea.

The southwestern Indian Ocean is monitored by RSMC La Réunion-Tropical Cyclone Centre/Météo-France (French) from its center on Reunion Island.

The RSMC Nadi-Tropical Cyclone Centre/Fiji Meteorological Service monitors the southwestern Pacific.

Australia’s area of responsibility includes the southeastern Indian Ocean, the Arafura Sea, the Gulf of Carpenteria, and the Coral Sea.

The Tasman Sea is monitored jointly by the TCWC-Wellington/Meteorological Service of New Zealand and the TCWC-Jakarta/Indonesian Meteorological and Geophysical Agency(partly in Indonesian).

Finally, the Solomon Sea and Gulf of Papua are monitored by the TCWC-Port Moresby/National Weather Service, Papua New Guinea (website is under construction, but this page is live).

Tropical cyclone scale comparison

Now it’s time to decide which is the more dangerous of the two storms mentioned above – Miami’s Category 3 or the Category 4 heading for Perth.

To do that, refer to this excellent table made and posted by Australia’s Bureau of Meteorology.
 


Australian name Australian category US US Saffir-Simpson category scale NW Pacific Arabian Sea /Bay of Bengal SW Indian Ocean South Pacific (East of 160E)
Tropical low Tropical depression Tropical depression Depression or severe depression Tropical depression Tropical depression
Tropical cyclone 1 Tropical storm Tropical storm Cyclonic storm Moderate tropical storm Tropical cyclone (Gale)
Tropical cyclone 2 Tropical storm Severe tropical storm Severe cyclonic storm Severe tropical storm Tropical cyclone (Storm)
Severe tropical Cyclone 3 Hurricane 1 Typhoon Very severe cyclonic storm Tropical cyclone Tropical cyclone (Hurricane)
Severe tropical cyclone 4 Hurricane 2 – 3 Typhoon Very severe cyclonic storm Intense tropical cyclone Tropical cyclone (Hurricane)
Severe tropical cyclone 5 Hurricane 4 – 5 Typhoon Super cyclonic storm Very intense tropical cyclone Tropical cyclone (Hurricane)

 
Your eyes weren’t deceiving you – all else being equal, both Miami and Perth are in about the same amount of trouble.

However, note that in Australia the term “severe tropical cyclone” encompasses the entire Saffir-Simpson scale. Visiting Aussies should know that in the US only the last three categories are called “major” hurricanes. This doesn’t mean that Saffir-Simpson categories 1 and 2 are fun…they’re also very dangerous and cause a lot of damage.

Whether you call them hurricanes, typhoons, tropical cyclones or cyclonic storms, forewarned is forearmed. Now that you have an overview of hurricane categories to go by, you will know what to expect when heavy weather looms while you are traveling.
 
 
 
Sources:

Typhoons, Hurricanes and Tropical Cyclones in the World. Digital Typhoon.

Tropical Cyclone FAQ. NOAA.

Tropical Cyclone Programme. World Meteorological Organization (UN)

Tropical Cyclone Scales. Wikipedia.

Tropical Cyclone Intensity and Impacts. Australian Bureau of Meteorology.

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