World Meteorological Day 2015: climate knowledge for climate action

Each year on 23rd March, National Weather Services around the globe celebrate World Meteorological Day.  This marks the establishment of the World Meteorological Organization (WMO) on this day in 1950. WMO is the global co-ordinating agency for meteorological and hydrological activities, formed because weather simply doesn’t limit itself to national boundaries.  World Meteorological Day is an occasion to commemorate the work that national meteorological and hydrological agencies undertake 24 hours a day, 365 days per year – work that produces weather forecasts and warnings to help keep our communities safe.  The recent passage of Cyclone Pam near Vanuatu and past New Zealand are timely reminders of these efforts.

Collecting weather data …

The routine collection of weather data is one part of MetService’s international responsibilities under the Global Observing System (GOS). Worldwide, weather agencies take observations of pressure, temperature, wind and rainfall around the clock. Data come from ships, buoys, weather balloons and land-based weather stations, and are transmitted via the WMO Global Telecommunication System (GTS). This is a world-wide stream of data used as input into global weather forecast models. The better we can “start off” (initialise) the global computer models as to the current state of the atmosphere, the better the future state will be predicted – and the more accurate the weather forecast will be for your place.

In New Zealand alone, hundreds of weather stations from Stewart Island to Cape Reinga tell us how wet, warm, or windy it is every hour, as well as measuring pressure and humidity. Weather balloons are released twice daily at several locations around the country. Recently, MetService has collaborated with the U.K. MetOffice to enable kiwis to share their local weather data on the ‘Your Weather’ section of metservice.com via the ‘Weather Observation Website’ (WOW) system.

… for climate knowledge, too

This year, the theme for World Meteorological Day is ‘climate knowledge for climate action.’ This is a timely focus. Globally, 2014 was the warmest year on record and fourteen of the fifteen hottest years have occurred this century. But how do we know this? That’s right – we looked back at historical weather data.

Think of climate as the sum of all the weather. If you smooth out all of the edges looking at things longer-term (from a climate perspective), it is possible to more clearly understand what is going on. Climate patterns such as the El Nino Southern Oscillation and the Southern Annular Mode are more ‘visible’ this way, including their effect on New Zealand wind, rain and temperature.

Reanalysis data’ is a very important tool for scientists trying to unlock the physical mechanisms behind our climate – trying to understand why we had a wet month, a warm year, or an active Cyclone season. Reanalysis datasets input historical weather data from around the globe into the same climate model, and extend it back over time. The relationships found in the past can help us forecast the future – this is the basis of seasonal climate predictions. For example, El Nino springs tend to be very cold in New Zealand, due to frequent southerly airstreams over the country. When we know an El Nino spring is coming, and in the absence of other major climate factors, the odds are that we’re in for an unusually cold spring.

Global temperature data (departure from normal), based on three different reanalysis datasets.    The data all tell the same story – a rapid increase in global average temperature since the 1960s.
Global temperature data (departure from normal), based on three different reanalysis datasets. The data all tell the same story – a rapid increase in global average temperature since the 1960s.

There are many examples of when historical weather data helps put things into climatic context. For example, people have asked, “is Cyclone Pam the worst Tropical Cyclone to hit the South Pacific?”.  The answer relies on good data being available.  Since Cyclone Zoe (2002) and Cyclone Pam (2015) both reached an estimated minimum central pressure of 890hPa, it looks like a tie.  And although satellites provide a relatively short record, their data can also help answer questions about Tropical Cyclone frequency. No increase in Tropical Cyclone numbers has been observed in the South Pacific over the last few decades since reliable satellite data have been available.

Number and intensity of cyclones in the South Pacific 1969-2014

Peter Lennox, MetService Chief Executive, is New Zealand's Permanent Representative with the United Nations World Meteorology Organization.
Peter Lennox, MetService Chief Executive, is New Zealand’s Permanent Representative with the United Nations World Meteorology Organization.

MetService also contributes to international climate activities directly.  MetService CEO Peter Lennox is New Zealand’s Permanent Representative to the World Meteorological Organization.  In addition, MetService has supported several major climate initiatives in New Zealand recently.

MetService and NIWA have collaborated to achieve official Global Climate Observing System (GCOS) Reference Upper Air Network status for the NIWA atmospheric research station at Lauder in Central Otago.

This is only the fourth upper-air site to be certified in the world, and the first in the southern hemisphere. Well-calibrated atmospheric observations are crucial to documenting climate and climate change. The standard network of upper-air meteorological observations, and also weather satellites, provide good coverage – but high-quality observations are needed against which these standard observations can be calibrated. The pairing of Lauder observations and MetService’s Invercargill radiosonde data will achieve the necessary calibration.

NASA's super pressure balloonAnd NASA’s super pressure balloon is awaiting lift off at Wanaka, being delayed due to adverse winds associated with Cyclone Pam. Designed to drift eastwards at an altitude of 110,000 feet (‘near space’), NASA expects the super pressure balloon to circumnavigate across South America and then South Africa, on its potentially record-breaking flight. Depending on the stratospheric wind speeds, the balloon should circumnavigate the earth every one to three weeks. The flight goal is to exceed the current super-balloon flight record of 54 days, and to maintain a constant float altitude. If the balloon test is validated, this opens the door for relatively inexpensive atmospheric research. You can track the balloon here.

Tropical Cyclone Reuben

MONDAY UPDATE

Cyclone Reuben crossed latitude 25 South overnight last night, with the Wellington Tropical Cyclone Warning Centre assuming high seas warning responsibility for the system this morning. As Reuben continued to move southwards it weakened, and at midday today (NZDT) was re-classified as an extra-tropical low.

Visible satellite image of ex-TC Reuben at midday NZDT. (image courtesy JMA)
Visible satellite image of ex-TC Reuben at midday NZDT. (Satellite image courtesy JMA)

The deep convection surrounding the cyclone has now sheared away from the low level circulation – a key feature of the extra-tropical transition that cyclones go through as they exit the Tropics. A high seas gale warning remains in force near the low centre, which is expected to linger in the sub-tropics and may even drift northwards again in the coming days as a weak feature.

 


 

SUNDAY AFTERNOON UPDATE

At 1pm today (Sunday 22nd March) RSMC Nadi named the 4th tropical cyclone of the season in the South Pacific basin for which they are responsible. TC Reuben was located near 23.2S 175.6W at 0000 UTC today (1pm NZDT), which is about  220km south of Nuku’alofa in Tonga. At that time, the central pressure was 995hPa making Reuben a category 1 cyclone.

Satellite image from 1:30pm NZDT today (Sunday 22nd March) showing the location of TC Reuben. (MTSAT image via NOAA)
Satellite image from 1:30pm NZDT today (Sunday 22nd March) showing the location of TC Reuben. (MTSAT image via NOAA)

TC Reuben is moving slowly south-southeast over the open ocean and is forecast to intensify a little in the next 24 hours. Current computer model guidance shows the system posing no threat to New Zealand in the coming days.

Track map for TC Reuben issued by RSMC Nadi based on the 0000 UTC (1pm NZDT) position.
Track map for TC Reuben issued by RSMC Nadi based on the 0000 UTC (1pm NZDT) position.

MetService meteorologists will continue to monitor Reuben closely and will be liaising with colleagues in Fiji at RSMC Nadi as the system approaches the Wellington Tropical Cyclone Warning Centre area of responsibility.

We’ll post further updates for TC Reuben on Monday.

TC Pam Summary

CHRIS NOBLE, MANAGER PUBLIC WEATHER SERVICES

Now that Cyclone Pam has passed the Chatham Islands, here’s a look back at events of the last couple of weeks…

History

Tropical Cyclone Pam began life as a tropical disturbance north of Vanuatu, officially numbered “TD11F” on the 6th March by RSMC Nadi in Fiji.  Over the following days the system slowly strengthened, reaching tropical depression status on 8th March, and following further intensification was named as Tropical Cyclone Pam at 7pm NZDT on 9th March.  Initial forecast tracks suggested TC Pam would continue to intensify and pass between Vanuatu and Fiji, before moving out of the tropics and southeast towards East Cape, New Zealand.

TC Pam strengthened quickly and eventually moved directly across the southern islands of Vanuatu during Fri 13th and Sat 14th March as a powerful category 5 cyclone, causing widespread destruction on some islands, as well as sadly leading to a number of fatalities.  At its peak, just south of Vanuatu, the central pressure reached 896hPa at 1pm NZDT on 14th March, with sustained winds of 250km/h near the centre of the system, making Pam one of the most intense and deadly cyclones on record in the South Pacific.

A microwave image of Severe Tropical Cyclone Pam soon after its peak intensity and crossing Vanuatu on Saturday 14th March. This type of imagery provides a unique view of the structure of cyclone by looking through the cold cirrus clouds and into the convective rainbands spiralling around the centre.
A microwave image of Severe Tropical Cyclone Pam soon after its peak intensity and crossing Vanuatu on Saturday 14th March. This type of imagery provides a unique view of the structure of cyclone by looking through the cold cirrus clouds and into the convective rainbands spiralling around the centre.

 

TC Pam Track Map

The full track for Tropical Cyclone Pam, through to 1am this morning (Wednesday 18th March), is shown below. Times in this image are in UTC (add 13 hours for NZDT).

2015-03-17-1200-tc-pam-track

 

 

Initial MetService commentary and forecasts for New Zealand

On Monday 9th March, before TC Pam was named, MetService meteorologists began regular issues of both press releases and blog entries to keep New Zealanders up to date with the latest official advice.

By Wed 11th March, two days before TC Pam moved across Vanuatu, the following Severe Weather Outlook was issued, focusing on the potential for adverse weather in the northeast of the North Island:

The Severe Weather Outlook issued at 2:34pm on Wednesday 11th March.
The Severe Weather Outlook issued at 2:34pm on Wednesday 11th March.

At this early stage, TC Pam was expected to track southeast from the Tropics and offshore from the North Island, although computer models differed somewhat in how close Pam would pass to East Cape.  For example, here’s the snapshot of a selection of global models posted to the MetService blog on the Wed 11th looking at the forecast position of the centre for 1am Monday 16th March:

Pic3

As you can see above, some models initially expected the centre to pass close to East Cape, while others took a track further offshore.

By Thursday 12th March, the day before TC Pam moved onto Vanuatu, the forecast track in the global models was becoming more certain and the following track map was issued late afternoon. It showed the centre passing offshore from East Cape, with the range of possible tracks including the centre crossing the northeast of the North Island:

Forecast path of cyclone Pam

 

First Severe Weather Watches and Warnings for NZ

As model forecasts converged and the track for TC Pam became clearer, the first Severe Weather Watch was issued at 9:52am on Friday 13th March for gales and heavy rain starting from Sunday night. This Watch included gales affecting Northland, Coromandel Peninsula, Great Barrier Island, eastern Bay of Plenty and Gisborne, and heavy rain affecting eastern Northland, Coromandel Peninsula, Gisborne and northern Hawkes Bay.  An updated Watch on Friday afternoon also highlighted the threat of dangerous wave conditions affecting eastern coasts of the North Island starting near Cape Reinga and eventually spreading as far south as the Wairarapa.

The following morning (Saturday 14th March), at 9:13am, the first Severe Weather Warning was issued alerting to heavy rain in Gisborne, northern Hawkes Bay and the ranges of eastern Bay of Plenty, and severe gales affecting Bay of Plenty (east of Edgecumbe) and Gisborne.  Subsequent warnings issued Saturday evening and on Sunday added eastern Northland and Coromandel Peninsula to the heavy rain warning, and eastern Northland, Great Barrier Island and Coromandel Peninsula to the strong wind warning.

 

Oceanic Warning handover from Fiji to New Zealand

As with all tropical cyclones moving out of the tropics and crossing latitude 25S, official warning responsibility passes from RSMC (Regional Specialised Meteorological Centre) Nadi in Fiji to the Wellington Tropical Cyclone Warning Centre in New Zealand.  For TC Pam, this happened in the early hours of Sunday morning (the 15th) with Nadi issuing their last high seas warning at 1am on Sunday, followed by Wellington issuing at 7am Sunday. The hand-over process requires careful co-ordination between the forecasting centres in Nadi and Wellington.

 

Re-classification

As Pam moved over colder oceans and into stronger upper level winds in the atmosphere, its structure changed.  Tropical cyclones in the Tropics are “warm-cored” in nature and have a near vertical structure, but as they move into the mid-latitudes strong upper level winds help “shear” the circulation, moving the supporting convection away from the storm’s centre and allowing colder air to wrap into the system. This process is called extra-tropical transition, and when it occurs, the responsible warning centre “reclassifies” the cyclone.  Note however, this does not necessarily mean that weather conditions improve.  Instead, the cyclone can, and did, remain very powerful and gales and heavy rain can spread further from the centre affecting a wider area.

 

Impacts on New Zealand

As TC Pam approached northern New Zealand, rain set in over the Far North during Sunday morning while winds over the upper North Island steadily increased.

The period from Sunday morning to Tuesday morning captures the main rainfall over the North Island associated with the passage of TC Pam to the east.  The following maps show the 24 hour accumulations from Sunday morning to Monday morning and from Monday morning to Tuesday morning respectively:

24-hour-rain-maps

Peak wind gusts recorded at MetService North Island weather stations were:

Kaeo Radar: 148km/h Sunday evening
Channel Island: 144km/h Sunday night
Hicks Bay: 144km/h Monday afternoon

The pressure trace at Hicks Bay (closest North Island weather station to the track of Pam) shows how the pressure there responded to the approach and passage of Pam with a lowest pressure of 974.7hPa at midday on Monday:

hix-pressure
This graph covers the 72 hour period from 1pm Sat 14th to 1pm Tuesday 17th March.

As well as wind and rain, very large seas were expected to affect eastern coasts of the North Island.  Surfers in Mt Maunganui commented that the swells were some of the largest they had witnessed while roads around East Cape were inundated by debris as highlighted in the following photos:

In summary, here’s the event records:

tc-pam-stats

 

 

Warning Verification

As with all Severe Weather Warnings issued by MetService, warnings for this event were logged and verified. The following images highlight the areas covered by warnings with a selection of observations:

rain-verification

wind-verification

 

Final words…

Pam has now passed the Chatham Islands and is moving away to the east over the Pacific Ocean as an intense extra-tropical cyclone. Conditions on the Chatham Islands should gradually ease as detailed in the recent Strong Wind Advisory, while an Oceanic Storm Warning remains in force for the system over the Pacific.

During this event, in addition to the numerous regular forecasts produced daily, MetService meteorologists published frequent blog posts, press releases and briefing statements for our clients across all sectors in New Zealand including emergency managers, various media agencies both locally and internationally, along with the general public. MetService.com set a new record for visitor numbers on Sunday 15th March – exceeding stats from TC Lusi one year ago in March 2014.

While New Zealand largely escaped the wrath of Pam, the same cannot be said for Vanuatu. Please spare a thought for our neighbours to the north as the disaster relief effort there continues. A number of aid agencies are appealing for donations including:

New Zealand Red Cross

Unicef New Zealand

Oxfam New Zealand

Save the Children New Zealand

 

Tropical Cyclone Pam Updates – Sunday 15 March 2015

Sunday 15 March 2015 10pm

RAMON OOSTERKAMP, MANAGER FORECASTING OPERATIONS

At 9pm Tropical Cyclone “Pam”, a Category 3 Cyclone, is lying near 32.8S 178.5E, or about 500km east-northeast of Cape Reinga moving swiftly southeast at 55 km/h. We are expecting “Pam” to recurve a little southward before passing about 150km east of East Cape at midday tomorrow.

Winds are increasing along eastern shores of Northland, through the Hauraki Gulf, Coromandel and Bay of Plenty. Southeast winds are currently gusting 110 to 120km/h in exposed places, with waves of 4.5 metres near Tutukaka. There are reports of homes without power in Kamo, Whangarei.

Reclassification of Tropical Cyclone Pam is expected to occur near 35S, which at this stage is likely to be early Monday morning.

Tropical cyclones begin their life cycle by feeding on the warm waters to our north, they require at least 26°C to form. Once they move out of the tropics they begin to change their structure, and as the sea surface temperature decreases, it becomes harder to maintain deep convection near the centre. In tropical cyclones, the strongest winds are near the centre, and, as the cyclone evolves, the strongest winds move away from the centre. Another clue that this evolution is happening is the loss of a symmetrical look.

The image on the left is TC Pam at 9pm on Saturday (Cat 5 – 890hPa) and the one on the right is Pam at 6pm Sunday (Cat 3 – 955hPa)
The image above is TC Pam at 9pm on Saturday (Cat 5 – 890hPa) and the one below is Pam at 6pm Sunday (Cat 3 – 955hPa)

pam at 05Z 15 Mar

You can clearly see the loss of structure, symmetry, and the eye! The strongest winds have decreased from 130 knots to 80 knots, but gales have spread out to affect a much larger area. The eye has filled, and the cyclone is beginning to look somewhat ragged; all evidence that Pam will soon evolve from a tropical cyclone to a mid latitude cyclone .

Reclassification does not mean that “Pam” no longer poses any threat. Extremely strong wind gusts, heavy rain and phenomenal waves are still expected, and details can be found in http://www.metservice.com/warnings/home as well as in http://blog.metservice.com/ or http://www.metservice.com/national/home

The next update to this blog will around midnight Sunday 15 March .

Sunday 15 March 2015 8pm

ARNO DYASON, METSERVICE METEOROLOGIST

TC Pam to the north of New Zealand at 11am this morning.
TC Pam to the north of New Zealand at 11am this morning.

Currently cyclone Pam is situated 450km to the north of the New Zealand coastline and still tracking southeast at 55m/h. It is expected to lie about 150km east of East Cape (northern Gisborne) by midday Monday, then move away from the New Zealand coastline towards Chatham Island.

 

Track of TC Pam. The orange lines mark the uncertainty of the track. Times are given in UTC, add 13 hours for New Zealand local time.
Track of TC Pam. The orange lines mark the uncertainty of the track. Times are given in UTC, add 13 hours for New Zealand local time.

 

ECMWF model showing the low centre to the east of the north island at midday Monday 16 March.
ECMWF model showing the low centre to the east of the north island at midday Monday 16 March.

Strong southeast winds and rain are expected over much of the North Island tonight and Monday, along with extremely large seas about the east coast. Wind gusts of 160 km/h or more are possible about the eastern Bay of Plenty and northern parts of Gisborne. Winds of this strength are likely to cause damage to trees and powerlines and could lift roofs and make for hazardous driving conditions. A burst of heavy rain accompanies these winds, with 180-220 mm possible about the Gisborne ranges. Please refer to the latest severe weather warnings and watches issued by MetService for more information.

Significant combined waves in metres for midnight Sunday 15 March (left), midday Monday 16 March (middle) and midnight Monday 16 March (right).
Significant combined waves in metres for midnight Sunday 15 March (left), midday Monday 16 March (middle) and midnight Monday 16 March (right).

The image above shows the total combined waves (sea and swell) generated by cyclone Pam, which are expected to rise to 7-8m around the northern New Zealand coastline and even up to 9m around the northern Gisborne coast.

For any further information go to: http://www.metservice.com/national/home
The next update to this blog will be around midnight Sunday 15 March.

Sunday 15 March 2015 16:00 pm

ARNO DYASON, METSERVICE METEOROLOGIST

At 1pm this afternoon (NZ local time) Tropical Cyclone Pam was located about 500km to the north of New Zealand. TC Pam has weakened somewhat in the last 6 hours, therefore being downgraded to a category 4 cyclone and forecast to weaken to a category 3 cyclone overnight. Pam is expected to lie about 150km east of East Cape (northern Gisborne) by midday Monday.

Visible satellite image of tropical cyclone Pam (left).
Visible satellite image of tropical cyclone Pam (left).
Rain radar (right) at 3pm Sunday 15 March 2015.
Rain radar (right) at 3pm Sunday 15 March 2015.

The satellite image (left) shown above clearly shows thick cloud bands with embedded thunderstorms around the centre of the low producing heavy rain over the ocean north of New Zealand. Outer rain bands have spread over Northland and Auckland as seen in the above radar image (right).

 

Track of TC Pam. The orange lines mark the uncertainty of the track. Times are given in UTC, add 13 hours for New Zealand local time.
Track of TC Pam. The orange lines mark the uncertainty of the track. Times are given in UTC, add 13 hours for New Zealand local time.

 

The latest analysis indicates that the system will remain classified as a tropical cyclone when it passes to the northeast of Gisborne by midday tomorrow with average wind speeds of up to 140km/h near the center of the low. Please refer to the latest severe weather warnings and watches issued by MetService for more information.

Sunday 15 March 2015 10:30am

FULONG LU, METSERVICE METEOROLOGIST

Satellite picture for the Tropics at 7am NZDT 15th March 2015
Satellite picture for the Tropics at 7am NZDT 15th March 2015
Track of TC Pam. The orange lines mark the uncertainty of the track. Times are given in UTC, add 13 hours for New Zealand local time.
Track of TC Pam. The orange lines mark the uncertainty of the track. Times are given in UTC, add 13 hours for New Zealand local time.

Tropical Cyclone Pam (now Category 4) has moved across 25S into TCWC Wellington (MetService NZ) area of responsibility early this morning. At 7am today (Sunday 15 March), it was located at 26.8S 172.7E or 850 kilometres north of Cape Reinga, moving southeast 52 km/h. The storm has sustained winds of 205 km/h near the centre, with gales extending out to about 400 kilometres from the centre. On its southeast track, Tropical Cyclone Pam is expected to lie about 620 kilometres north-northeast of Cape Reinga at 1pm this afternoon, and about 420 kilometres north of East Cape at midnight tonight, and about 240 kilometres east of East Cape at midday Monday. Heavy rain and strong wind warnings and watches are in force for the northern and eastern parts of the North Island from this evening through to Tuesday.

Please refer to our warnings page for details at MetService warning home page.

Apart from heavy rain and severe gales, Tropical Cyclone Pam is expected to bring heavy swells to the North Island east coasts from Northland to Hawke’s Bay, with 4 to 6m near the coast, and 6 to 8m offshore. People considering venturing near or into the water, are advised to take extra precautions, especially when winds are onshore, and to check the latest forecasts for expected dangerous conditions.

Next update will be at or no later than 16:00 NZDT Sunday 15 March 2015.

Sunday 15 March 2015 5am

MATTHEW FORD, METSERVICE METEOROLOGIST

At 1am this morning (NZ local time) Severe Tropical Cyclone Pam was located over waters about 500km southeast of Noumea, New Caledonia, moving quickly south-southeast at 45 km/h. TC Pam is still a category 5 cyclone but has begun a weakening trend.

Infrared satellite image of tropical cyclone Pam, 3.44am Sun 15th March 2015
Infrared satellite image of tropical cyclone Pam, 3.44am Sun 15th March 2015

The above infrared satellite image of TC Pam is colour coded to show the temperature of the cloud tops. An eye is still clearly visible in the centre of the image, but the surrounding cloud tops, which are a band of intense thunderstorms, are not as cold as they were at this time yesterday (refer to yesterday’s 5am blog update for a comparison). The green colour indicates the cloud top temperature of the thunderstorms surrounding the eye is about -65C, while this time yesterday they were -82C, suggesting that the cyclone has weakened. However, winds near the centre are still estimated to be over 200 km/h.

The latest track map issued by RSMC Nadi (below), shows TC Pam taking a southeast track to the north of New Zealand. As TC Pam moves southeast over cooler waters it should continue to weaken, but will still be an intense storm with hurricane force winds near the centre out to midnight tonight.

TC Pam forecast track map issued by RSMC Nadi 2.17am Sun 15 March 2015
TC Pam forecast track map issued by RSMC Nadi 2.17am Sun 15 March 2015

TC Pam has now moved into the Wellingon Tropical Cyclone Warning Centre area of responsibility, so future cyclone tracks will be issued by MetService. The system is expected to bring heavy rain, severe gales and high seas to parts of the North Island. Please refer to the latest severe weather warnings and watches issued by MetService for more information.

Tropical Cyclone Pam Updates – Friday 13 March 2015

Update Friday 13th March at 7:00pm

FRANCES RUSSELL, METSERVICE METEOROLOGIST

Satellite picture for the Tropics at 7pm NZDT 13th March
Satellite picture for the Tropics at 7pm NZDT 13th March

Confidence continues to grow in the projected path for Severe Tropical Cyclone Pam. There is currently a Severe weather watch in force, http://www.metservice.com/warnings/severe-weather-watch. Watches and Warnings will continue to be added and updated on our website and this is the first place that they will appear. Meanwhile, The Ministry of Civil Defence and Emergency Management are encouraging those in possibly affected areas to head on over to http://getthru.govt.nz/disasters/storms/ for more information.

What can we expect as TC Pam moves towards New Zealand?

The forecast shows TC Pam is expected to decay to Category 4 once it moves south of New Caledonia, but models show it will have remarkable persistence as it travels on towards New Zealand. MetService has issued a Severe Weather Watch for northern and eastern parts of the North Island. This covers the period when the storm tracks to the east of the North Island during Monday and Tuesday and highlights the risk of severe gales and heavy rain and large seas.
Large waves, as well as storm surge, are likely to have a significant effect as the cyclone passes by New Zealand. Very large, long period waves are likely from Cape Reinga to East Cape on Sunday and Monday, extending south to include Gisborne to the Kaikoura Coast on Monday and Tuesday. Waves of this size have significant potential for coastal erosion, especially combined with gales and storm surge.

How is TC Pam affecting the Pacific right now?

TC Pam is currently Category 5 located 120km northnortheast of Port Vila and 100km eastsoutheast of Lamp, Vanuatu, tracking southsouthwest over Vanuatu, where a Tropical Cyclone Warning is in place for destructive winds, torrential rain and phenomenal seas today and Saturday morning before things ease. The red rings around TC Pam indicate areas of destructive storm force winds and very destructive hurricane force winds. Wind speeds near the centre are currently 240km/h and the area of gales around the storm extends out greater than 300km. In the last 6 hours from 1pm Pekoa Aiport on the island of Espiritu Santo in Vanuatu recorded 107 mm of rainfall.

The latest forecast track map from RSMC Fiji, 1423 NZDT  Friday 13 March 2015.
The latest forecast track map from RSMC Fiji, 1423 NZDT Friday 13 March 2015.

The next update to this blog will be around 6am Saturday 14 March.

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Update Friday 13th March at 1:00pm

ROB KERR, METSERVICE METEOROLOGIST

Satellite picture for the Tropics at 1pm NZDT 13th March
Satellite picture for the Tropics at 1pm NZDT 13th March

Confidence continues to grow in the projected path for Severe Tropical Cyclone Pam and MetService has issued a Severe Weather Watch for northern and eastern parts of the North Island. This covers the period when the storm tracks to the east of the North Island during Monday and Tuesday and highlights the risk of severe gales and heavy rain. Watches and Warnings will continue to be added and updated on our warnings page and this is the first place that they will appear (you can sign up here to receive them by email, another great way to stay right up to date). Meanwhile, The Ministry of Civil Defence and Emergency Management are encouraging those in possibly affected areas to head on over to http://getthru.govt.nz/disasters/storms/ for more information.

What can we expect as TC Pam moves towards New Zealand?

The forecast shows TC Pam is expected to decay to Category 4 once it moves south of New Caledonia, but models show it will have remarkable persistence as it travels on towards New Zealand. These two images show the output from the various models for 1pm Monday afternoon and 1am Tuesday morning.

1pm Monday:

An updated selection of different global models showing mean sea level pressure for 1pm NZDT on Monday 16th March. Pressures lower than 1000hPa have been coloured blue.
An updated selection of different global models showing mean sea level pressure for 1pm NZDT on Monday 16th March. Pressures lower than 1000hPa have been coloured blue.

1am Tuesday:

An updated selection of different global models showing mean sea level pressure for 1am NZDT on Tuesday 17th March. Pressures lower than 1000hPa have been coloured blue.
An updated selection of different global models showing mean sea level pressure for 1am NZDT on Tuesday 17th March. Pressures lower than 1000hPa have been coloured blue.

Whilst there is still a little variation in the timing of its passage, the path of the storm shows excellent consistency across all these models.

How is TC Pam affecting the Pacific right now?

Meanwhile, TC Pam is currently tracking southwards and affecting Vanuatu, where a Tropical Cyclone Warning is in place for destructive winds, torrential rain and phenomenal seas today and Saturday morning before things ease. The red rings around TC Pam indicate areas of destructive storm force winds and very destructive hurricane force winds. Wind speeds near the centre are currently 220km/h and the area of gales around the storm extends out 300km.

The latest forecast track Map from RSMC Fiji, issued at 8:24am Friday Morning
The latest forecast track Map from RSMC Fiji, issued at 8:24am Friday Morning

Large waves, as well as storm surge, are likely to have a significant effect as the cyclone passes by New Zealand. Very large, long period, waves are likely from Cape Reinga to East Cape on Sunday and Monday, extending south to include Gisborne to the Kaikoura Coast Monday and Tuesday.

Wave spectra for Whakatane and Gisborne respectively below. Note the very long period waves (14-18 seconds) and the size (4+m). The longer the wave period, the more energy is contained within these waves and the better they reflect around obstacles such as islands and headlands.

Wave spectra chart for Whakatane
Wave spectra chart for Whakatane
Wave spectra chart for Gisborne
Wave spectra chart for Gisborne

[end]

Update Friday 13th March at 8:30am

JOHN LAW, METSERVICE METEOROLOGIST

Satellite image for 7am NZDT 13th March 2015
Satellite image for 7am NZDT 13th March 2015

Severe Tropical Cyclone Pam, currently a Category 5 cyclone moves southwards across Vanuatu while TC Nathan, Category 2, lingers off the coast of Queensland and is forecast to return to the east across the Coral Sea.

Just visible on this image is another tropical feature, this one is on the other side of the equator in the northern hemisphere. Tropical cyclone Bavi is forecast to move northwest over the next few days. Notice how the cloud wrapping into TC Pam is clockwise while in the north it is anticlockwise.

The Meteorological service of Vanuatu have issued warnings for many parts of the county for gales, heavy rain and large swells.

Tropical Cyclone Pam Updates – Thursday 12 March 2015

Update Thursday 12th March at 5:30pm

JOHN LAW, METSERVICE METEOROLOGIST

The forecasting team continue to monitor the progression of Tropical Cyclone Pam. By comparing the forecast tracks of several models the team have compiled a best track forecast for the position of the centre of the system as it tracks southwards.

Using the most recent data the system is forecast to pass just to the east of East Cape during the Monday. However, there is still a large degree of uncertainty in the exact path of the cyclone and although the centre may not pass over New Zealand, Severe Weather is likely to affect parts of the country – especially the northeast of the North Island. Stay up to date with the latest warnings here: http://metservice.com/warnings/home

In the diagram below the best forecast positions are indicated by the red line while the surrounding grey envelope gives an idea of the spread in the tracks the cyclone could take. Adverse weather associated with the cyclone may spread much wider than this envelope of tracks. With still several days to go, the forecast is likely to change and the team will continue to bring you the latest information.

Forecast path of cyclone Pam
Forecast track of Cyclone Pam shon in red, The surrounding grey envelopegives an idea of the spread in the tracks the cyclone could take.

The latest Severe Weather Outlook has been issued providing more information of severe weather forecast later in the weekend and into the early part of next week. Find out more at http://metservice.com/warnings/severe-weather-outlook

Find out more about what we mean by Severe Weather in this blog post: http://blog.metservice.com/2013/10/warnings-watches-and-outlooks/#

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Update Thursday 12th March at 11.00am

JOHN LAW, METSERVICE METEOROLOGIST

Tropical Cyclone Pam remains in the tropics and continues to intensify. Currently a category 4, which by definition has mean winds between 86 and 107 knots (157-198 km/h), the track of the system remains southward just to the east of the southern Solomon Islands and Vanuatu.

TC Pam position as at 10am 12 March 2015
TC Pam position as at 10am 12 March 2015

The latest forecast from the Fiji Meteorological Service is for the cyclone to become a category 5 (mean wind speeds in excess of 107 knots or 198 km/h) at around 7am on Friday 13th (New Zealand time); at this stage the forecast position is to the east of northern Vanuatu.

TC Pam track from Fiji Met Service

Staying in the tropics, Tropical Cyclone Nathan remains off the coast of Queensland and is joined by another Tropical Cyclone, Olwyn, which is off the coast of Western Australia and will not affect New Zealand. For more information about these cyclones, head to Australia’s Bureau of Meteorology website.

What are the impacts on New Zealand?

We are still several days away from the cyclone reaching New Zealand waters and there is still plenty of uncertainty in the models. Knowing where the system moves is important in calculating the severity of the impacts on New Zealand.

MetService’s forecasting team look at information from a selection of different global models which use equations to model the physical properties of the atmosphere. Here are the latest model outputs for 1pm on Monday 16th March:

Model outputs for 1pm on Monday 16th March

 

As you can see, the general consensus of the models is for the lowest pressure to stay off to the north and the east of the country – but that does not mean we will avoid getting some stronger winds, heavy rainfall and high seas with this feature.

For the very latest thoughts from MetService’s meteorologists, head over to the Severe Weather Outlook which is updated by 15:00 NZST every day.

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