Tropical Cyclone Names

February and March are the peak months for tropical cyclones in the South Pacific.

The first storm in our area this season was named TASHA on Christmas Day, it very quickly made landfall near Cairns.  TASHA played a small part in the annual wet season that has proved so extreme over northern Australia during December and January.

Cyclone VANIA was the second of the season, named near Vanuatu on 12 January. It was followed by VINCE, named on the same day off NW Australia, then by ZELIA which was named on 14 January in the Coral Sea.  On 22 January,  WILMA was named near Samoa and the next day ANTHONY was named in the Coral Sea.

Tropical Cyclone WILMA , 7am Fri 28 Jan 2011

The History of naming storms

Christopher Columbus was the first recorded writer about tropical cyclones.  For several hundreds of years storms were named arbitrarily: an Atlantic storm that ripped the mast off a boat named Antje became known as Antje’s hurricane.  In the Spanish-speaking islands of the Caribbean, storms were named after the Saint’s day on which they arrived.

Near the end of the nineteenth century, Clement Wragge, an Australasian meteorologist, named tropical cyclones (and droughts) after political figures.  It is recorded that on occasion he described the tropical cyclone in uncomplimentary terms, such as causing distress, displaying erratic behaviour, wandering aimlessly, or frequently changing its mind.

During World War II when American bomber crews flew missions from Micronesian to Japan, they informally used the names of girlfriends and wives for the tropical cyclones they encountered.  In the early 1950s, American meteorologists used their phonetic alphabet (ABLE, BAKER, CHARLIE, etc.,) to identify tropical cyclones in the Atlantic. Starting in 1953, female names in alphabetical order were used by the US National Weather Service.  In the late 1970s, the lists of names were extended to include alternating male and female names.

Who names the names?

When winds rotating around the core of a cyclone in the tropics build to gale force, the cyclone is given its own name to uniquely identify it.  This is done by the appropriate Tropical Cyclone Warning Centre (TCWC).  The current list of available names is prepared well in advance by the Tropical Cyclone Committee of the World Meteorological Organisation (WMO) through its World Weather Watch and Tropical Cyclone Programmes.

Traditionally, the tropical cyclone formation areas are divided into seven basins (see map).  To help monitor cyclone activity in these basins the WMO Tropical Cyclone Programme has established Tropical Cyclone Warning Centres (TCWCs) for each basin. Their areas of responsibility extend across the regional boundaries of the Regional Specialized Meteorological Centres (RSMCs) of the WMO, which are outlined in red on the map.  The RSMCs have regional responsibility to provide weather advisories, bulletins and warnings on tropical cyclones, while the TCWCs supplement this work by observing, naming and forecasting tropical cyclones.

In our region, MetService operates the Wellington RSMC, working closely with the Nadi TCWC and the Nadi RSMC (operated by the Fiji Meteorological Service) to coordinate on the various bulletins and warnings for our respective areas of responsibility. MetService also serves as a backup for the Nadi TCWC in the event that Nadi experiences an outage. The Australian Bureau of Meteorology runs a TCWC at Brisbane. The naming boundary between the Brisbane and Nadi centres is along longitude 160 degrees East, which explains why the names of cyclones heading for New Zealand may seem to jump around the alphabet.

The Tropical Cyclone Committee provides each TCWC its own list of names.  These are chosen to be short, familiar to users, and easy to remember so that their use helps communicate warnings, especially when multiple cyclones have formed.  The names are used in alphabetical order, alternating male and female, but occasionally letters such as Q are skipped.  A name may be skipped if it is deemed inappropriate for some reason – e.g., a similarly-named cyclone is already active in the area, or it is the name of a public figure currently in the news.  Cyclones retain the same name if they cross a regional boundary (except in the Indian Ocean) or if they decay and then regenerate.

For more information on cyclone names click here, or here (NOAA), or here (WMO).

In regions such as the NW Pacific and the Atlantic each season starts with A on the list.  In our part of the world the lists are used sequentially, so the first name used each season is the one immediately following the last one used.

In the AUSTRALIAN list, this season started with Tasha, followed by Vince, then  Zelia.  Their next alphabet is: Anthony, Bianca, Carlos, Dianne, Errol, Fina, Grant, Heidi, Iggy, Jasmine, Koji, Lua, Mitchell, Narelle, Oswald, Peta, Rusty, Sandra, Tim, Victoria, and Zane.

In the FIJI list, this season started with Vania, followed by Wilma, Yasi, and Zaka.  Their next alphabet is: Atu, Bune, Cyril, Daphne, Evan, Freda, Garry, Heley, Ian, June, Kofi, Lusi, Mike, Nute, Odile, Pam, Reuben, Solo, Tuni, Ula, Victor, Winston, Yalo, and then Zena.

CATEGORIES

Mariners may have heard of the intensity of a tropical cyclone given as a category between one and five.  Worldly mariners will have noted that the Category Scale used in the South Pacific is DIFFERENT from the Saffir-Simpson Category scale that is used around America.  For more details on this point, click here .

Here is a copy of the category scale that applies to the Australia/New Zealand area.

On average, there are 86 tropical cyclones each year with 47 reaching hurricane strength.  These systems act like safety valves, helping to spread out any build-up of heat in the tropical oceans.  In the South Pacific the annual average is between eight and ten, of which one is expected to reach New Zealand in nine years out of ten.  The South Pacific cyclone season is officially from the start of November to the end of April.

So, there may be a few more tropical cyclones forming in our area, especially during February and March.  Keep an eye out to the north at http://bit.ly/7daywx and at our wide-scale satellite image.

Forecasting for the Summer’s Day Sweepstakes

This blog post is about the MetService Summer’s Day Sweepstakes. I’d like to give you some background on how to use the material on the MetService website to give yourself an advantage in the Sweepstakes. The prizes are fantastic so it’ll be worth your effort.

The first thing you should do when you start thinking about your Sweepstake picks is to try and find out what’s happening with the weather now around NZ. To achieve this, look at recent weather mapssatellite imagery, rain radar and latest NZ observations. There’s information on how to read weather maps in our learning centre. Try and extrapolate what’s been happening, to give you a first estimate of what might occur in the future. Extrapolation is a valid method of forecasting if things advance consistently, but doesn’t work if they become chaotic.

Next you should look at the rain forecasts for 3 Days and 7 Days ahead. Draw on your knowledge and experience of New Zealand weather to infer from these maps what the general weather conditions are likely to be. Then, for each location, think carefully about how to adapt what the model is telling you for your picks.

A look through the MetService Blog may be useful if you expect something to occur in the weather that’s related to one of the posts.

There are three elements for you to forecast: temperature at noon, wind direction at noon, and rainfall for the day (24 hour total). Let’s look at these in turn:

Temperature at noon

The temperature at noon generally won’t be the highest for the day (the max usually occurs a couple of hours later). Try and estimate the direction from which the air will arrive – northerly winds are warmer, southerly winds are colder (as explained in the post on Rain or Showers). If the wind comes in from the sea, e.g. as a sea-breeze, it won’t be as warm by day as if it had originated over land. If the air is flowing over a mountain range, allow for warming due to the Foehn effect.

Take care to account for the exact position of the weather station where the forecast is being recorded. Big differences can occur in New Zealand, sometimes over a distance of a kilometre or less.

Wind direction at noon

On weather maps the wind blows approximately parallel to the isobars, anticlockwise around anticyclones and clockwise around depressions (lows). But in the summer, coastal locations often have a sea-breeze during the daytime that blows in from the sea; a similar but weaker effect occurs near lakes. The terrain can channel the wind too.

Winds in New Zealand can vary a lot from one place to another and, at any location, can blow from several different directions throughout the day.

Rainfall for the day (24 hour total)

Because you’ll be forecasting for a 24-hour period, any uncertainty about timing of a rainband shouldn’t affect your forecast unless you’re expecting it to come through close to either end of the period.

The 3 Day data give you rainfalls for the 3-hour period previous to each map time, and the 7-Day data give rainfalls for the corresponding 6-hour periods.

 

There’ll be five locations for you to forecast for: Whangarei, Taupo, Hokitika, Christchurch and one location of your choice. Some specific points to note about the four common locations:

Whangarei: north of Auckland, near the coast and away from large mountain ranges.

Temperature variations are moderated by the sea, and the temperatures are fairly high because of the latitude. Winds come from several directions, but a southwesterly is the most common; the sea-breeze is a southeasterly. Rain generally comes from moist northeasterly flows ahead of fronts crossing from the Tasman Sea. As fronts cross there’s typically a period of heavier rain, typically followed by showers arriving from the southwest.

 

Taupo: in the central North Island, next to the Lake.

At higher altitude than the other stations (400 metres above sea-level), but has a continental climate in summer with typically warm days. Not a great deal of wind because of sheltering from the surrounding mountain ranges, but any wind tends to be westerly. In summer Taupo can get heavy convective showers.

Hokitika: immediately west of the Southern Alps and near the coast.

Temperature variations are usually moderated by the sea, but can get a warm southeasterly Foehn. Winds are often northerly or westerly. Rain is strongly enhanced by uplift as a northwest flow approaches the Alps ahead of a front. Heavy showers can occur behind a front if the flow comes from a westerly direction.

Christchurch: east of the Southern Alps, near the coast and Banks Peninsula.

Often gets a northeasterly wind off the sea, but a nor’wester Foehn wind can push the temperature over 30C in summer. Doesn’t get a southeasterly because of obstruction from Banks Peninsula. Most rain comes from the east and south. Can get heavy convective showers in unstable southwesterly flows.

I hope this post gives you something useful to work with. Best of luck for the Sweepstakes!

New feature for metservice.com “towns & cities” – Past Weather

We have added a new feature to the “towns & cities” section on metservice.com. “Past Weather” is now located below the ten day forecast for most locations showing wind, air temperatures and rainfall in a graphical format.

The graph shows the elements for yesterday, the last 7 days, and the last 30 days, as well as ‘historical’ on a calendar monthly basis. The data is detailed further upon mouse-over and includes:

- the highest wind gust
- the direction the wind was blowing from
- the highest and lowest air temperatures; and
- rainfall

Here’s an example for Auckland Airport for “Yesterday”:

There is a drop-down menu to select other station locations in the vicinity of the town or city.

The Historical tab includes information about temperatures and rainfall, but not for wind. This is shown below:

Note that the long term ‘Historical Avg’ figures for air temperatures and rainfall are the averages of the highest, lowest or total over many years (including the last two), but the monthly figures for last year and the previous year are simply the highest or lowest temperature or total rainfall for that single month.

These days almost all meteorological observations are recorded by automated weather stations. Occasionally sensors go awry or there may be communications problems which result in some observations not being made or observations that are invalid. So, in the Past Weather displays some items may be missing …. these instances will be indicated by “n/a” meaning “not available”, or the display element may not appear at all.

We hope that you find this information to be interesting, informative and useful.

NIWA has made all these data available on an observation basis as well as derived statistics from them through their National Climate Database portal. The URL is http://cliflo.niwa.co.nz. Registration and agreement to terms is required, and it is free. Extensive help is provided; it is fairly straight forward.

We have provided this “Past Weather” information from MetService records from these stations so that there is a readily accessible visualisation of past weather in commonly understood time scales … day, week, month, year, and longer term (averages).