Climate Services » The Climate Of Vanuatu Tuesday, January 06, 2009
 The Climate Of Vanuatu
 
Introduction
Vanuatu luxuriates in a tropical maritime climate with characteristic uniform temperature, high humidity and variable rainfall. Winds are generally light except during a tropical storm. The climate of Vanuatu can be defined by two main seasons, the cold (dry) season from MAY to OCTOBER and the hot (wet/cyclone) season from NOVEMBER TO APRIL.
 
Location
The Y-shaped archipelago of Vanuatu stretches over some 1,300 km in the centre of a quadrangle marked by Fiji (to the east), Australia (west), Solomon Islands (north) and New Caledonia (south). (Cf. Appendix, Figure 1) The 83 islands, of which 65 are inhabited, have a total land area of 12,190 square kilometers. It lies between latitudes 13°S and 21°S and longitudes 165°E and 170°E. Most of the islands that make up the archipelago ranges from atolls to mountainous/volcanic with the highest peak about 1800 meters above mean sea level. Santo Island, the largest island in the chain, possesses the highest peak.
 
The Vanuatu territory including its marginal seas covers an area of approximately 700,000 square kilometers. The total population of the country is estimated in 2002 to be about 200,000 with an annual growth rate of 3.0% (UNDP, 2004).
Approximately 30% of the population lives in urban areas. The remaining 70% lives in rural villages ranging from a few families to several hundred people. Almost 80% of the population lives on seven islands: Efate, where the capital Port Vila is located, Santo, the largest island, Tanna, Malekula, Pentecost, Ambae and Ambrym (Vanuatu Government, 1999).
 
Time
The time Meridian is 165 degrees East, hence the time zone is Western Standard Time with 0000-hour midnight or 2300 hour Zulu (GMT)
 
Temperature
Being an equatorial country, Vanuatu has relatively uniform temperature throughout the year. The warmest month is February and the coolest is August. In the coastal areas, daily temperature average 26 °C in the hot season with an average maximum of 30°C and an average minimum of 24 °C. Extreme night-time minimum temperature in some coastal areas may reach 13°C.
Port Vila, the capital on the west coast of Efate has an average temperature of 25 °C with August averaging 23 °C and February 27 °C.
Rainfall Distribution
Rainfall is generally higher in the hot season than in the cold season. The seasonal windflow, coupled with the local topographic features determine the rainfall distribution patterns over the country. The predominant southeast wind-flow is often saturated with moisture and contributes to a highly variable rainfall pattern. 
 
Another major mechanism that produces rainfall in Vanuatu in the summer and especially during La Nina years is the South Pacific Convergence Zone (SPCZ) that often shifts over Vanuatu.
 
Orographic rainfall is a common feature on the main Islands. During the wet season, rainfall is particularly high on the windward side (southeast parts) of the bigger islands and scarce during the dry season especially on the leeward sides (northwest part). Rainfall is variable on the smaller islands depending on their location and size
 
Rainfall on the island of Efate shows this particular pattern. On the windward side, annual rainfall is measured from 2400 mm - 3000 mm and is almost half that amount on the leeward side.
 
The wettest month in Vanuatu is usually March and the driest month is August.
 
Afternoon showers are still a common feature of the weather in Vanuatu.
 
Winds
The predominant wind flows in any season are the trade winds from the east to southeast at about 5 knots. The wind flow during the summer (November to April) are generally light and variable. In the winter from May to October, the trade southeast wind flows become persistent and averaging at 10 knots.
 
Strong marine wind warnings over open waters are common in the winter season with speeds up to 25 knots. However, tropical cyclone and depression are also common, which can be responsible for high and disastrous winds in the summer.
Tropical Cyclone
 
The hot or wet season in Vanuatu, which is from November to April, is also known as the cyclone season. The geographical location of the archipelago in the southwest Pacific is on a route occasionally traversed by cyclones, which by definition are associated with winds of at least 34 knots (62 km/hr).
 
The area of Vanuatu (land and sea) receives about 2-3 cyclones in a cyclone season, and the greatest frequency is in January and February. On average, Vanuatu and its marginal seas is a common route to some 20 to 30 cyclones per decade, with 3 to 5 causing severe damage.
 
Cyclones are very erratic in their movement therefore often hard to predict, but they generally maintain their southerly movement until about 21 °S to 25 °S when they do a parabolic curve mostly to the east, and dissipate. The archipelago of Vanuatu being small islands grouped together in a north to south distribution are effected by almost every cyclone passing through.
Floods
Floodings are common on low-lying flood plains near rivers especially during tropical cyclones and during La Nina years. Prolonged rainfall during La Nina years often cause severe impacts to crops.
 
Droughts
Droughts in Vanuatu are related to the El Nino (ENSO – El Nino Southern Oscillation) phenomenon. During El Nino years when the SOI is on a negative phase, rainfall in Vanuatu is generally below average. The latest ENSO episodes, which resulted in dry conditions in Vanuatu, were in 1982/83, 1990/95 and the 1997/98. The worst drought year in Vanuatu was in 1993. However, during a normal year, drought effects can be experienced on rain-shadow areas during the dry season.