Part 1: Weather & Climate

Annual Temperature Range

What are the annual temperature ranges (high, low, average)?
Tonga’s annual temperature range is about 73.4 degrees Fahrenheit to 78.8 degrees Fahrenheit. The warmest month is March when the temperature doesn't typically reach above 86 degrees Fahrenheit. The coolest month is August when temperatures don't typically reach below 63 degrees Fahrenheit (1). Mean temperatures has increased by 0.4–0.8°C since 1970, with warming most rapid in the warmest season (November–April). Ha'apai is the name given to a chain of islands in Tonga, and the temperature of Ha’apai has increased by 0.4°C. This is significantly higher than the other islands of Tonga (2).

Precipitation Distribution

How is precipitation distributed over the year at your location? Which type (rain, snow, etc), timing, and amount?

Of the annual amount of rainfall, 60% to 70% of precipitation occurs during the wet season (November to April) and is mostly caused by tropical cyclones and El Nino events. Most of the country's 1600 mm average annual rain usually falls during this humid season, which is also a cyclone season (3).

Humidity Ranges

What is the humidity range of your location and the incidence of fog?
Humidity averages around 75%. January is the least humid month, with an average around 42% (4). The most humid month is May, with humidity reaching 99%. From mid February to mid December, humidity levels are above 56% (5).

Wind Direction & Global Wind Patterns

What are the predominant wind directions? Which global wind patterns (trade winds, westerlies, etc.) affect your location and how does this change over the year?

There is a characteristic strong west-wind, which makes crossings from east to west very difficult especially for sailing boats. Wind blows from southwest to northeast. During the year, Tonga is subjected to south-east trade winds resulting in light/average wind forces. However, this wind is most substantial from May to October. In addition, tropical cyclones bring heavy winds to the country (6).

Air Masses

Which types of air masses (and where are their source regions) affect your location and what time of year?

Tonga experiences the Maritime Tropical air mass throughout the majority of the year. Tonga is an island in the middle of the pacific and it experiences similar weather to most other island countries like Australia and New Zealand. Maritime Tropical air masses are usually moist, warm, and unstable (7).

Severe Weather

What weather systems and severe weather affect your location (and what time of year)? What causes these patterns?

Between the months of November and April, tropical cyclones are the most common extreme weather events experienced by Tonga. These storms lead to flooding and storm surges that are especially detrimental because of Tonga’s low lying terrain. Climate change exacerbates these effects of tropical cyclones on Tonga with rising sea levels. Luckily, big cyclones only occur every 10-15 years. Additionally, there have been three major droughts in Tonga, which have occurred in 1983, 1998, and 2006. All three have been directly linked to El-Nino events (8).

Temperature & Precipitation Regimes

What are the temperature and precipitation regimes for your location?

Tonga experiences a maritime temperature regime due to the islands being surrounded by water. Because the rainy season is between November and April, Tonga has a winter max precipitation regime (9).

Climate Type

Which climate type(s) does your location have? What are the characteristics of this climate?

Tonga has a wet-equatorial climate meaning it is hot and wet all year round. For the most part, rainfall occurs daily in places with this kind of climate. On Average, temperature only changes a few degrees over the course of the year (10).

Work Cited

1 - https://weatherspark.com/y/65544/Average-Weather-in-Tonga-Cameroon-Year-Round

2 - https://climateknowledgeportal.worldbank.org/country/tonga/climate-data-historical#:~:text=The%20mean%20annual%20temperature%20in,%C2%B0C%2D24%C2%B0C

3 - https://weather-and-climate.com/average-monthly-Rainfall-Temperature-Sunshine-in-Tonga

4 - http://www.met.gov.to/index_files/climate_summary_tonga.pdf

5 - ​​https://weatherspark.com/y/65544/Average-Weather-in-Tonga-Cameroon-Year-Round#Sections-Humidity

6 - https://www.meteoblue.com/en/weather/historyclimate/climatemodelled/tonga_cameroon_2221394

7- https://okfirst.mesonet.org/train/meteorology/AirMasses.html

8 - https://climateknowledgeportal.worldbank.org/country/tonga/vulnerability

9- http://www.met.gov.to/index_files/climate_summary_tonga.pdf

10- https://www.britannica.com/science/wet-equatorial-climate

*Graphs are linked directly to site by clicking on each image above.