|It is hurricane season, if you live in America. Despite the |
fact that Katrina and now Rita never touch this shore, the
media has been bombarding us with blow by blow antics
of the natural disasters that have been devastating the
US Gulf Coast.
Here, The Explainer gives the lowdown on hurricanes.
What are hurricanes and how do you forecast them?
The terms "hurricane" and "typhoon" are regionally specific
names for a strong "tropical cyclone". A tropical cyclone is
the generic term for a non-frontal synoptic scale
low-pressure system over tropical or sub-tropical waters
with organized convection (i.e. thunderstorm activity) and
definite cyclonic surface wind circulation.
Tropical cyclones with maximum sustained surface winds of
less than 17 m/s (34 kt, 39 mph) are called "tropical
depressions" (This is not to be confused with the condition
mid-latitude people get during a long, cold and grey winter
wishing they could be closer to the equator).
Once the tropical cyclone reaches winds of at least 17 m/s
(34 kt, 39 mph) they are typically called a "tropical storm"
and assigned a name. If winds reach 33 m/s (64 kt, 74
mph)), then they are called:
"Hurricane" (the North Atlantic Ocean, the Northeast Pacific
Ocean east of the dateline, or the South Pacific Ocean east
"Typhoon" (the Northwest Pacific Ocean west of the
"Severe tropical cyclone" (the Southwest Pacific Ocean west
of 160E or Southeast Indian Ocean east of 90E)
"Severe cyclonic storm" (the North Indian Ocean)
"Tropical cyclone" (the Southwest Indian Ocean)
Where do they get their names from?
Tropical cyclones are named to provide ease of
communication between forecasters and the general public
regarding forecasts, watches, and warnings.
Since the storms can often last a week or longer and that
more than one can be occurring in the same basin at the
same time, names can reduce the confusion about what
storm is being described.
The first use of a proper name for a tropical cyclone was by
an Australian forecaster early in the 20th century. He gave
tropical cyclone names "after political figures whom he
By properly naming a hurricane, the weatherman could
publicly describe a politician (who perhaps was not too
generous with weather-bureau appropriations) as 'causing
great distress' or 'wandering aimlessly about the Pacific.'"
(Perhaps this should be brought back into use ;-)
During World War II, tropical cyclones were informally given
women's names by US Army Air Corp and Navy
meteorologists (after their girlfriends or wives) who were
monitoring and forecasting tropical cyclones over the Pacific.
From 1950 to 1952, tropical cyclones of the North Atlantic
Ocean were identified by the phonetic alphabet
(Able-Baker-Charlie-etc.), but in 1953 the US Weather
Bureau switched to women's names. In 1979, the WMO and
the US National Weather Service (NWS) switched to a list of
names that also included men's names.
The Northeast Pacific basin tropical cyclones were named
using women's names starting in 1959 for storms near
Hawaii and in 1960 for the remainder of the Northeast
Pacific basin. In 1978, both men's and women's names were
The Northwest Pacific basin tropical cyclones were given
women's names officially starting in 1945 and men's names
were also included beginning in 1979.
Beginning on January 1, 2000, tropical cyclones in the
Northwest Pacific basin are being named from a new and
very different list of names. The new names are Asian
names and were contributed by all the nations and
territories that are members of the WMO's Typhoon
These newly selected names have two major differences
from the rest of the world's tropical cyclone name rosters.
One, the names by and large are not personal names. There
are a few men's and women's names, but the majority are
names of flowers, animals, birds, trees, or even foods, etc,
while some are descriptive adjectives.
Secondly, the names will not be allotted in alphabetical
order, but are arranged by contributing nation with the
countries being alphabetized.
The North Indian Ocean region tropical cyclones are not
The Southwest Indian Ocean tropical cyclones were first
named during the 1960/1961 season.
The Australian and South Pacific region (east of 90E, south
of the equator) started giving women's names to the storms
in 1964 and both men's and women's names in 1974/1975.
Who or what determine whether the names should be femi
nine like Rita or masculine like Andrew?
The names of hurricanes, typhoons, etc are decided by the
various Tropical Cyclone centres. The one in Miami decides
the names for the north Atlantic and northeast Pacific
How or when do storms become hurricanes?
Tropical Storms become hurricanes when mena wind speeds
Are hurricanes just synonymous with the Caribbean and
the Gulf Coast of the United States? Or do they happen
here in the UK and Europe and how regular do they occur?
Hurricanes are tropical features and require sea
temperatures of at least 27C to be maintained. Sea
temperatures round the UK are nowhere near that high,
even in high summer, so they cannot exist at our latitudes.
However, we do get the remnants of old hurricanes coming
out of the tropics, and they get entrained into the Atlantic
flow, causing some of the depression to be more active than
usual., as they add extra moisture and heat.
The infamous storm of October 1987 continued the
remnants of an old hurricane, and August 2004, saw at
least 3 ex-hurricanes come across the UK, giving a wetter
than average month. We can get hurricane force winds from
our normal winter storms, but we do not get hurricanes.
Are all hurricanes violent and how do you grade them?
Not all hurricanes are violent, and sometimes it is the heavy
rain that causes problems, rather than the strong winds.
The scale below refers to the Atlantic and northeast Pacific.
Hurricane strength is defined on the Saffir-Simpson scale
Category 1 sustained wind speeds of 74 to 95 m.p.h.
Category 2 sustained wind speeds of 96 to 110 m.p.h.
Category 3 sustained wind speeds of 111 to 130 m.p.h.
Category 4 sustained wind speeds of 131 to 155 m.p.h.
Category 5 sustained wind speeds greater than 155 m.p.h.
What is the worst hurricane ever in the world, Europe and
in the British Isles?
The 'worst' hurricane is difficult to judge, as there are some
variable, worst winds, most expensive, greatest loss of life,
Are we expecting any hurricanes in Europe anytime soon?
As mentioned earlier we do not get hurricanes in the UK or
Europe, but the remnants. Scotland has caught the
remnants of at least 2 if not 3 in recent weeks that have
come out of the tropics, but we do not envisage any from
the time being. Hurricane Rita looks like dissipating inland
over Texas, so does not threaten us, but there are over 2
months to go in the season, so we need to be vigilant.
With thanks to Robin Thwaytes at the UK Meteorological
For answers to questions on any news events please e-mail
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