Record rainfall turns Nuku'alofa into lakes

Nuku'alofa, Tonga

Photos by Pesi Fonua

Catholic Cathedral lake. Flooding in Nuku'alofa, Tonga, 11 June 2016.

Exceptionally heavy, unseasonal rainfall fell across Tongatapu on June 10-11 causing flooding in Nuku’alofa, and turning the capital into a city of lakes, during what is supposed to be the “dry season”.

Fua’amotu recorded 273.1mm of rainfall in the 24 hours between 1:00pm Friday and 1:00pm Saturday 11 June, according to Tonga Met. No rainfall for a 24 hour period in June has exceeded this amount in the last 36 years of records.

This is more than three times above the rainfall expected for the whole month of June - when total monthly rainfall historically averages around 79mm. It was also approaching the record rainfall levels for the year brought to Tonga by Cyclone Winston in February when 293.8mm fell in Vava’u in a 24 hour period, during the wet season.

It was also unusual because the rainfall forecast for June to August 2016 was for continuing drier than normal conditions for most of Tonga, when Tongans were warned to conserve water.

Football fields under 'Apifo'ou College lake. Flooding in Nuku'alofa, Tonga, 11 June 2016.

Cold front

On Friday evening heavy rain lashed Tongatapu as a cold frontal system moved slowly over Tonga, with a north to northwest windflow.

Trees fell onto power lines in Western Tongatapu causing power outages late on Friday affecting the whole of Tongatapu, with falling branches also causing hazards on roads.

Flooding caused roads closures. Parts of By Pass Road were closed while some roads at Kolomotu'a and low lying areas of Nuku'alofa remained unpassable until the flood water levels dropped on Sunday.

Nuku’alofa enjoyed a sunny afternoon on Sunday. The relative humidity dropped from 100% on Saturday to 98% on Sunday at Fua’amotu at 6:00am.

Laitia Fifita the duty meteorological officer said the system bringing the heavy rain had travelled all the way from the east coast of Australia, and dissipated over Tonga today. It was exceptional and not related to a tropical cyclone that might be expected to bring heavy rain, and was outside of the range of the predicted weather forecast for June.

"We do climate analysis on statistics and one of the setbacks of using statistical analysis is that it does not capture the dynamic systems that move in like this," he said.

Sunset under dark rainclouds, Nuku'alofa boat harbour, Tonga, 11 June 2016.

Extreme weather

This year has been a year of extreme weather for Tonga. The hottest day in Tonga's recorded history was 35.5C at Niuafo’ou on February 1 this year, when a long heatwave was experienced during the month prior to Cyclone Winston reaching Tonga.

Historically, the climate of Tonga is characterized by the contrast between a wet season from November to April, and a dry season from May-October. About 60% of the rain is expected in the rainy season, but this year was characterized by below average rainfall.

In 2011 a Pacific Climate change science program predicted that Tonga’s Rainfall patterns would change over this century with more extreme rainfall days expected.

Tonga Met has supported the theme of World Meteorological Day this year – warning of climate change that is: “Hotter, drier, wetter: face the Future.”

On March 23 this year the Secretary General of the United Nations World Meteorological Organization, Mr Petteri Taala said the “future is happening now”. Of the world’s climate he stated, “the alarming rate of change we are now witnessing in our climate as a result of greenhouse gas emissions is unprecedented in modern records.” This included shattered temperature records, intense heat waves, exceptional rainfall, devastating drought and unusual tropical cyclone activity.

In 36 years, figures from the Fua'amotu Weather Centre for June show there has been nothing like the weekend's 24 hour rain experienced before during the same month (although 2006 experienced a high monthly rainfall totalling 359 mm the largest single day rainfall in June 2006 was 63mm on 9 June and 72mm on 30 June 2006).

Rainfall for Fua'amotu from 1980 to 2015 for the month of June (mm).