Question 1. What Is A Tropical Cyclone?
A tropical cyclone is defined as a non-frontal low pressure system of synoptic scale developing over warm waters having organised convection and a maximum mean wind speed of 34 knots or greater extending more than half-way around near the centre and persisting for at least six hours.
Every cyclone is unique varying according to a number of factors including life cycle, intensity, movement, size and impact (wind, storm surge and flooding).
Question 2. Explain Me What About Tsunamis?
A tsunami is a series of ocean waves with very long wavelengths (typically hundreds of kilometres) caused by large-scale disturbances of the ocean, such as:
- volcanic eruptions
These disturbances can either be from below (e.g. underwater earthquakes with large vertical displacements, submarine landslides) or from above (e.g. meteorite impacts). They are not caused by tropical cyclones.
Question 3. Why And How Are Cyclone Names Chosen?
Tropical cyclones are named to provide ease of communication between forecasters and the general public regarding forecasts, watches, and warnings. Having a name also raises the profile of the cyclone heightening the public’s awareness. Since the storms can often last a week or longer and that more than one can be occurring in the same region at the same time, names can also reduce the confusion about what storm is being described.
The Bureau of Meteorology maintains a list of names (arranged alphabetically and alternating male and female). A name remains on the list until its corresponding cyclone severely impacts the coast (e.g. Larry and Vance). The name is then permanently retired and replaced with another (of the same gender and first letter). It can take over 10 years from the time a name is put on the list to when it is first used to name a cyclone.
Question 4. What Is The Eye And Eye Wall?
The circular eye or centre of a tropical cyclone is an area characterised by light winds, fine weather and often clear skies. The eye is the region of lowest surface pressure
The size of the eye varies from one cyclone to the next ranging from 10 km to over 100 km. The eye diameter of severe cyclones off the northwest coast tends to be about 20 to 40 km, and are typically smaller than those in some other parts of the world such as the north Pacific. The eye size of Tracy (Darwin, 1974) was just 12 km across. Rosita (Broome, 2000) only had an eye diameter of 20 km.
Question 5. How Are Tropical Cyclones Different From Tornadoes?
While both tropical cyclones and tornadoes are atmospheric vortices, they have little in common. Tornadoes have diameters on the scale of hundreds of metres and are usually produced from a single thunderstorm. A tropical cyclone, however, has a diameter on the scale of hundreds of kilometres and contains many thunderstorms. Tornadoes are primarily an over-land phenomena as solar heating of the land surface usually contributes toward the development of the thunderstorm that spawns the vortex (though over-water tornadoes have occurred). In contrast, tropical cyclones are purely an oceanic phenomena – they die out over-land due to a loss of a moisture source. Lastly, tropical cyclones have a lifetime that is measured in days, while tornadoes typically last on the scale of minutes.
Question 6. What Is The Tropical Cyclones Intensity Scale? How Is This Different From The Usa Intensity Scale?
The severity of a tropical cyclone is described in terms of categories ranging from 1 (weakest) to 5 (strongest) related to the maximum mean wind speed as shown in this table.
Note: corresponding approximate wind gusts and central pressure are also provided as a guide. Stronger gusts may be observed over hilltops, in gullies and around structures.
Question 7. What Does ‘maximum Sustained Winds’ Mean? How Does It Relate To Wind Gusts In Tropical Cyclones?
The Bureau of Meteorology uses a 10 minute averaging time for reporting the sustained (i.e. relatively long-lasting) winds. The maximum sustained wind are the highest 10 minute surface winds occurring within the circulation of the cyclone. These surface winds are those observed (or, more often, estimated) to occur at the standard meteorological height of 10 m having an unobstructed exposure.
Gusts are a wind peak lasting for just a few seconds. Typically, in a cyclone environment the value for a peak gust is about 25 % higher than a 10 minute sustained wind. Barrow Island and Mardie sustained wind and wind gust profile during TC Monty (2004).
Question 8. How Do Tropical Cyclones Form?
For a cyclone to form several preconditions must be met:
- Warm ocean waters (of at least 26.5°C) throughout a sufficient depth (unknown how deep, but at least on the order of 50 m). Warm waters are necessary to fuel the heat engine of the tropical cyclone.
- An atmosphere which cools fast enough with height (is “unstable” enough) such that it encourages thunderstorm activity. It is the thunderstorm activity which allows the heat stored in the ocean waters to be liberated for the tropical cyclone development.
- Relatively moist layers near the mid-troposphere (5 km). Dry mid levels are not conducive for allowing the continuing development of widespread thunderstorm activity.
- A minimum distance of around 500 km from the equator. Some of the earth’s spin (Coriolis force) is needed to maintain the low pressure of the system. (Systems can form closer to the equator but it’s a rare event)
- A pre-existing disturbance near the surface with sufficient spin (vorticity) and inflow (convergence). Tropical cyclones cannot be generated spontaneously. To develop, they require a weakly organised system with sizeable spin and low level inflow.
- Little change in the wind with height (low vertical wind shear, i.e. less than 40 km/h from surface to tropopause). Large values of wind shear tend to disrupt the organisation of the thunderstorms that are important to the inner part of a cyclone.
Having these conditions met is necessary, but not sufficient as many disturbances that appear to have favourable conditions do not develop.
Question 9. How Much Data Do You Look At When Developing A Weather Forecast?
On a clear day when it’s really simple, you can put one together in 30-40 minutes. On a day like today (hot and humid), you can be looking at things for hours. If I know there’s a big event coming, I’ll spend three or four hours a day easy looking at it before I get to work.
Question 10. What Is The Storm Prediction Center?
The Storm Prediction Center (SPC) is a part of the National Weather Service (NWS) and is one of nine National Centers for Environmental Prediction.
Question 11. Why Do Tropical Cyclones Form?
The sun heats the tropical areas more than the polar regions. If there were no wind, then the tropics would keep getting hotter and hotter, and the poles would get colder and colder. The atmosphere’s basic function is to redistribute heat from the equator to the poles, and tropical cyclones are one mechanism by which this occurs. However it is still quite remarkable that such a thing as a tropical cyclone should arise. It has been said that if we had not actually observed tropical cyclones then, despite all we know about the physics of the atmosphere, we would never have guessed at their existence.
Question 12. What Is Storm Surge?
Storm surge is a large mound of water that accompanies a tropical cyclone as it comes ashore. The intense winds of the cyclone pile up the ocean into a dome of water that is pushed onshore as the cyclone strikes the coast. The low pressure of the cyclone adds to the height of the mound of water, though this is a secondary effect. When the height of a storm surge is discussed it does not take into account the height of the large waves on top of the mound of water.
Question 13. How Can I Find Out About Severe Weather Warnings?
Warnings of severe weather for the UK are issued by our National Meteorological sService, the Met Office. We also post a warning on the front page of our site. Follow this link to find out what severe weather warnings are in place today.
Question 14. What Do You Consider An Accurate Forecast?
The biggest thing everybody’s going to notice is the temperature because that’s something that happens every day. I try to keep that within three degrees. My goal is when there’s a big event coming in, I expect to get those right.
Question 15. What Happens To Cyclones As They Move Further South?
Cyclones off northern Australia typically develop between 5 and 15°S and reach maximum intensity between 10 and 20°S. As they move further south they will weaken over land or, for those remaining over water, weaken as they encounter an unfavourable environment (strengthening wind shear) and move over cooler water. They usually increase in speed as the steering winds in the mid-levels of the atmosphere increase and move to the south or southeast.
Question 16. When Did The Naming Of Cyclones Begin?
The convention of naming Australian tropical cyclones began in 1964. The first Western Australian named cyclone was Bessie that formed on 6 January 1964. Female names were used exclusively until the current convention of alternating male and female names commenced in 1975.
The naming of weather systems in Australia began much earlier than the 1960s, however. The flamboyant Clement Wragge, Government meteorologist in Queensland from 1887 until 1902, initiated the practice by naming weather systems after anything from mythological creatures to politicians who may have annoyed him.
Question 17. How Much Time Off Do You Get/take?
I’ve been at KRDO Newschannel 13 for more than ten years so I get about 3 weeks off per year plus some sick time.
Question 18. What’s The Hardest Part About Forecasting?
The fact that things can change at a moment’s notice. One small change in something in the atmosphere can mess up your whole forecast.
Question 19. How Big Are Tropical Cyclones?
The size of a cyclone is usually described in terms of the radius of gale-force (sustained winds of at least 63 km/h). Although the distribution of surface winds is never completely symmetrical estimates of the gale-radius provide a reasonable guide on the size of a system. Cyclones off the northwest have an average radius of gales of about 150 to 200 kilometres. It is common for gales to occur well beyond the average radius of gales in one quadrant, for example the northwesterly monsoon winds to the north of the centre.
Question 20. How Are Tropical Cyclones Different To Mid-latitude Cyclones?
To a first approximation a tropical cyclone is like a heat engine – it derives its energy from the heat that is released when water vapour that has been evaporated from the ocean surface (assisted by high winds and low pressure) condenses in the middle of the atmosphere. Mid-latitude cyclones (low pressure systems associated with fronts) primarily get their energy from horizontal gradients in temperature.
Another important difference between the two is that tropical cyclones have their strongest winds near the surface while mid-latitude systems have their strongest winds many kilometres above the surface near the top of the atmosphere.
Question 21. Tell Me Do You Get An Adrenaline Rush When All Those Watches And Warnings Start Popping Up?
Yeah. I think back to Mapleton (tornado two years ago). We were on the air for four and a half hours straight without a break, without a commercial. We had warnings popping up and reports coming in. There’s no more of an adrenalin rush than spring storms.
Question 22. What Is The Difference Between A Storm Surge And Storm Tide?
The combination of storm surge and astronomical tide is known as ‘storm tide’. The worst impacts occur when the storm surge arrives on top of a high tide. When this happens, the storm tide can reach areas that might otherwise have been safe.
Question 23. How Is A Severe Tropical Cyclone Different From A Non-severe Cyclone?
Tropical cyclones are classified as severe when they are producing ‘very destructive winds’ having sustained surface winds of at least 118 km/h near the centre and gusts of at least 165 km/h. This corresponds to cyclone categories 3, 4 and 5.
Question 24. What Is The Difference Between Australian Tropical Cyclones And Cyclones, Typhoons And Hurricanes In Other Parts Of The World?
For historical reasons tropical cyclones are called different names in different parts of the world. The terms hurricane and typhoon are regionally specific names for a severe tropical cyclone (sustained winds of more than 118 km/h (64 knots). Hurricane is used in the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160E. Typhoon is used in the Northwest Pacific Ocean west of the dateline.
For many parts of the world a non-severe tropical cyclone is referred to as a tropical storm and assigned a name.
Question 25. What Do The Terms Damaging Winds, Destructive Winds And Very Destructive Winds Mean?
The term damaging winds refers to wind gusts in excess of 90 km/h. The term destructive winds refers to wind gusts in excess of 125 km/h. The term very destructive winds refers to wind gusts in excess of 165 km/h.
Question 26. How Does The Amount Of Damage Caused By A Cyclone Increase As The Wind Speed Increases?
As wind speed increases the power of the wind to do damage increases exponentially. Hence a category 5 severe tropical cyclone (with wind gusts > 280 km/h) has the potential to do around 250 times the damage of a Category 3 severe tropical cyclone (with wind gusts of 165 km/h). This underscores the importance of the category system.
Question 27. What Is The Life-cycle Of A Tropical Cyclone?
Tropical cyclones have a distinct life cycle. For cyclones that reach at least severe (category 3 or higher having wind gusts of at least 165 km/h) the life-cycle may be divided into four stages. For non-severe cyclones, their development is constrained by one or more of a number of factors such as being located in an unfavourable atmospheric environment, movement over cooler water or making landfall.
The formative stage : On satellite images the disturbance appears as an unusually active, but poorly organised, area of convection (thunderstorms). The circulation centre is usually ill-defined but sometimes curved cumulus cloud bands spiralling towards an active area of thunderstorms indicate the location of the centre. Initially the amount of convection near the centre is dependent upon the normal diurnal cycle of tropical convection, increasing overnight and subsiding during the day. As development occurs the convection persists throughout the day. The strongest surface winds may be well removed from the centre, tend to occur in disorganised squalls and are often confined to one quadrant, for example the northwesterly monsoon winds to the north of the centre. Apart from local squalls the maximum wind is usually less than gale force. When formative stage tropical cyclones move inland they produce little or no damage on landfall but are often associated with heavy rain and sometimes flooding over northern Australia.
The immature stage : In this stage the area of convection persists and becomes more organised. Intensification occurs simultaneously. The minimum surface pressure rapidly drops below 1000 hPa and convection becomes organised into long bands spiralling inwards. Gale-force winds develop with the strengthening pressure gradient, and the maximum winds (which now may be storm-force or more) are concentrated in a tight band close to the centre. The circulation centre is well defined and subsequently an eye may begin to form. In satellite images several well organised curved bands of active convection may be seen spiralling in towards a central dense mass of clouds covering the focal point of the banding, or surrounding the centre. The eye (if it exists) may be masked by a canopy of cirrus cloud, which itself may contain curved striationsassociated with the outflow at the top of the tropical cyclone. The immature tropical cyclone can cause devastating wind and storm surge effects upon landfall, although damage is usually confined to a relatively small area. In this stage of development very rapid intensification can occur and the associated structural changes observed when the cyclone is under radar surveillance can sometimes be confusing.
The mature stage : During this stage the tropical cyclone acquires a quasi-steady state with only random fluctuations in central pressure and maximum wind speed. However, the cyclonic circulation and extent of the gales increase markedly. Asymmetries in the wind field may also become more pronounced. In satellite images the cloud field is highly organised and becomes more symmetrical. The more intense cyclones are characterised by a round central dense overcast containing a well-centred, distinct round eye. The surrounding convective bands are tightly coiled and quasi-circular. Typically a cyclone spends just a day or so at maximum intensity until it begins to weaken, unless the cyclone remains in a highly favourable environment.
The decay stage : The warm core is destroyed during this stage, the central pressure rises, and the belt of maximum wind expands away from near the centre. Decay may occur very rapidly if the system moves into an unfavourable atmospheric or geographic environment, but sometimes only the tropical characteristics are modified while the cyclonic circulation moves on to higher latitudes.
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