Update for Tuesday afternoon, 10 March 2015

JOHN LAW, METSERVICE METEOROLOGIST

The latest guidance and advice from the Fiji Meteorological Service has upgraded Tropical Cyclone Pam to a category 2. This means that sustained wind speeds close to the centre of the system are in excess of 90km/h. The system is forecast to continue strengthening as it moves slowly to the southeast. At 1pm, New Zealand time, TC Pam was located at 9.7°S 170.4°E, with a central pressure of 985hPa. The latest track and position information can be found on the Fiji Met Service website.

Locating the centre of the tropical system is an important task and can be complicated by the presence of large amounts of high cloud and the lack of surface observations over the Pacific. One tool at the disposal of tropical specialists is microwave imagery of the tropical cyclone – which provides a unique view inside the cloud bands surrounding the cyclone.

Microwave imagery of TC PAM This microwave image, from the American Naval Research Lab, has been coloured to highlight the deepest and most active cloud bands around the cyclone, shown in red and orange. Microwave imagery such as this can “see through” high cirrus cloud that might otherwise obscure the cyclone in traditional satellite imagery.

Where is Pam heading?

As the tropical system heads southwards it will be closely monitored by the meteorologists at MetService. This is just one of many possible tracks based on global model data. Note that while there is a general consensus on a track like this, the actual track and speed of the cyclone may be different and it will be important to keep up to date with the forecast.

Forecast Track TC Pam This images shows one of several possible forecast traks for the tropical system.

One of the models that the forecasting team will be looking at is the one from the UK Met Office. You can find the latest output from this model here on metservice.com: http://www.metservice.com/maps-radar/rain-forecast/rain-forecast-5-day. Again, this is just one of many possible solutions, but as we've shown in the multi-model images, most of the models are in broad agreement. As the system moves southwards out of the tropics it will move over cooler waters causing the system to weaken.

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Update for Tuesday morning, 10 March 2015

JOHN LAW, METSERVICE METEROLOGIST

The track map for TC Pam issued earlier today by RSMC Nadi shows the cyclone intensifying to a Category 3 (on the Australian intensity scale) during Wednesday. As the cyclone moves south, it should begin to accelerate to the east of Vanuatu over the next few days, reaching almost as far south as Fiji by Friday morning.

2015-03-09-18utc-track-map Forecast track map for TC Pam issued by RSMC-Nadi based on the analysis position at 7am, 10th March 2015. The grey shaded area shows the range of possible tracks the cyclone could take in the future.

The latest satellite image shows TC Pam over open waters north-northeast of Vanuatu, surrounded by a broad area of convection.

Infrared satellite image from midday (NZDT) Tuesday 10th March, 2015. Image courtesy JMA. Infrared satellite image from midday (NZDT) Tuesday 10th March, 2015. Image courtesy JMA.

 

Whilst this is still a long way from New Zealand, MetService will continue to monitor TC Pam closely, as we issue a series of South Pacific Guidance charts every day as part of our responsibilities to the WMO’s Severe Weather Forecasting and Disaster Risk Reduction Demonstration Project (SWFDDP).

As an example, below is the chart valid for midnight on Wednesday. The dotted line indicates a change in threat level for swell heights: to the south a minimum of 3.5m swells are considered significant, whereas to the north where there are many low lying island nations, swells of 2.5m or more are considered significant. The core of strongest winds associated with TC Pam should not affect any of the land areas in the region over the next couple of days, but the swells those winds generate will fan out and could pose a significant threat to places like Tuvalu.

Part of the Southwest Pacific Guidance set produced each day by Lead forecasters at MetService. This chart is valid at 1am on Thursday 12th March. Part of the Southwest Pacific Guidance set produced each day by Lead forecasters at MetService. This chart is valid at 1am on Thursday 12th March.

Looking further ahead to when TC Pam will reach the New Zealand area, the image below shows the low centre tracking east of New Zealand late on Sunday, according to a variety of global computer models from different agencies. This image is for 1am Monday 16th March, 24 hours after the image posted in the Monday 10 March blog.

TC Pam multi-model 12UTC 15th March A selection of global models showing mean sea level pressure for 12UTC on Sunday 15th March (1am Monday NZDT). Pressures lower than 1000hPa have been coloured blue.

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