Sat. Nov 23rd, 2019

Understanding tropical cyclone scales and categories

Cyclone KennethCyclone Kenneth, a Category 4 storm, is expected to wreak havoc on the northern regions of Mozambique.

understanding tropical cyclone scales and categories 1024x777 - Understanding tropical cyclone scales and categories

cyclone 1200x910 - Understanding tropical cyclone scales and categories

With Tropical Cyclone Kenneth expected to make landfall in
Mozambique on Thursday night, it’s important to understand the scales and
categories which indicate the destructive capability of these fierce weather
systems.

It’s important to note that hurricanes, cyclones, and typhoons
are all, fundamentally, the same weather phenomenon. The only difference
between the three is their relation to where they are formed. These formations
and classifications correlate directly to the oceanic conditions. A rotating
storm system characterised by a strong low-pressure centre:

  • When formed over the Atlantic and Northeast Pacific is known as a hurricane.
  • When formed over the Northwest Pacific is known as a typhoon.
  • When formed over the South Pacific and the Indian Ocean is known as a cyclone.

Cyclone season, within the Southern African context, generally
begins in the warm summer months and peters out towards the tail end of autumn.
The 2018/2019 South-West Indian Ocean cyclone season officially began on
November 15, 2018, and will end on April 30, 2019. This season, in particular,
has proven to be the deadliest cyclone period in Africa, with the most daunting
test still on the horizon.

Cyclone Idai

Tropical Cyclone Idai made landfall in Mozambique in Mid-March
of 2019. Before dissipating, it left in its wake a trail of natural devastation,
the likes of which had never before been witnessed on the African continent. The
Category 3 Cyclone killed over 1000 people across three neighbouring countries:

  • Mozambique – 602 fatalities
  • Zimbabwe – 344 fatalities
  • Malawi – 60 fatalities

Cyclone Idai also displaced over three million residents.
Affected countries are still struggling to house those whose homes were
destroyed. The absolute destruction of vital infrastructure, including healthcare
facilities and power generating units, has also led to a Cholera epidemic which
is threatening to ravage the region as an aftereffect of the storm.

As countries struggle to recover from this natural disaster,
the imminent arrival of Cyclone Kenneth threatens further destruction in a time
of crisis.

Cyclone Kenneth

Cyclone Kenneth, a Category 4 storm, is expected to wreak havoc on the northern regions of Mozambique. The destruction is expected to spread into Tanzania, a country which is rarely affected by the weather phenomenon.

Residents have been urged to evacuate their homes and seek refuge on higher ground, as torrential rainfall and storm surges are expected to result in widespread flash flooding.

Understanding tropical cyclone scales and categories

The most commonly used scales to identify cyclonic intensity
are the Saffir–Simpson scale (SSHWS) and the Meteo France’s La Reunion tropical
cyclone centre (MFR). Categories on the SSHWS scales are ranked according to
winds speeds as follows:

ssc - Understanding tropical cyclone scales and categories
Table via Wikipedia

Classifications on the MFR scale are ranked on a Tropical
Cyclone Intensity Scale which also uses wind speed as a key metric:

MFR - Understanding tropical cyclone scales and categories
Table via Wikipedia

Rainfall and storm surge

In addition to extreme wind speeds, torrential rainfall and
oceanic surges are major contributors to the destructive power of tropical
cyclones. While these aren’t officially marked on a scale, rain and surge
predictions are relative to both the SSHWS and MFR scales.

Tropical Cyclone Kenneth is expected to bring with it up to
1500mm of rain in Mozambique’s coastal regions over the next five days. Tanzania
will also be affected with up to 500mm of rain expected in places. Storm surges
of up to five metres are also expected.

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