Tropical Cyclone Pam Updates - Tuesday 10 March 2015

Update for Tuesday afternoon, 10 March 2015


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.

Sea State and Swell

By Sarah Haddon, Meteorologist

The MetService team produces both coastal and recreational marine forecasts. Part of these forecasts includes the state of the sea and the swell. But what is the difference?

Firstly, it is important to understand how a wave is described. Figure one shows the different characteristics of a wave.

The Southern Annular Mode (or SAM)

New Zealand lies mid-way between the tropics and the Southern Ocean, and our day-to-day weather can arrive from either direction. On a longer time scale (weeks to months), tropical weather is influenced by the state of the El Nino-Southern Oscillation (ENSO). The ENSO climate pattern affects wind flows, rainfall distribution and sea temperatures right across the tropics, from equatorial South America to Indonesia. It also has some effect on New Zealand’s climate (winds, temperatures and rainfall patterns), although generally to a lesser degree than in the tropics.

Understanding MetService’s Recreational Marine Forecasts

Besides the coastal waters, the MetService forecasting team produces marine forecasts for a number of smaller areas where there is a lot of recreational boating activity. These forecasts are routinely issued four times every day; they are monitored continually and updated more frequently if conditions warrant it.

Recreational Forecasts

The recreational forecasts are written for high-use recreational areas: Bay of Islands, Auckland, Coromandel, Bay of Plenty, Hawke Bay, Kapiti, Mana, Wellington, and Christchurch.

Understanding MetService's Coastal Marine Forecasts

MetService's forecasting team produces marine forecasts for New Zealand coastal waters. These forecasts are routinely issued four times every day; they are monitored continually and updated more frequently if conditions warrant it.

Coastal Forecasts

Forecasts for coastal waters cover the area from the coastline to 60 nautical miles (about 100km) out to sea. The New Zealand coast is divided into 18 areas, as shown in figure 1:

Weather balloons

Weather balloons have been released for decades around New Zealand to record data throughout the lower layers of the atmosphere. They have been used to measure everything from the base of low cloud to atmospheric wind and temperature profiles. One of the first people to use weather balloons was French Meteorologist Léon Teisserenc de Bort. He released hundreds of weather balloons from his observatory in Trappes, France. His experiments lead to the discovery of the tropopause and the stratosphere.