Unseasonal, record-breaking rainfall floods Tonga

Unseasonal, record-breaking rainfall floods Tonga

The Kingdom of Tonga was hit by an exceptionally heavy, unseasonal rainfall and very strong winds on June 10 and 11, 2016, causing heavy flooding in the Pacific nation and turning the capital Nuku’alofa in a city of lakes. The severe weather, brought by the same storms that battered Australia more than a week ago, caused major damage, coastal erosion, and widespread flooding. It did, however, bring some relief to the drought-stricken country.

Fua’amotu airport recorded 273.1 mm (10.75 inches) of rainfall in the 24 UTC hours of Friday, June 10, according to the Tonga Meteorological Services. In the last 36 years of records, no rainfall for a 24 hour period in June has exceeded this amount, Matangi Tonga Online reports.

This is more than three times above the rainfall expected for the whole month of June - when total monthly rainfall historically averages around 79 mm (3.11 inches). It was also approaching the record rainfall levels for the year brought to Tonga by the Tropical Cyclone "Winston" in February 2016 when 293.8 mm (11.56 inches) fell in Vava’u in a 24 hour period. TC Winston formed in Tonga's wet season, but this record-breaking storm came in the middle of what was suppose to be the dry season.

The weather system also brought strong winds that tore down trees and power lines. Trees fell onto power lines in Western Tongatapu, causing power outages late on Friday affecting the whole of Tongatapu, the main island of Tonga. The falling branches also caused hazards on roads.

72 hours of rainfall accumulation ending Jun 13, 2016 at 09:00 UTC. Credit: NASA/JAXA GPM; Google

Laitia Fifita, the duty meteorological officer, said the system bringing the heavy rain had traveled all the way from the east coast of Australia, and dissipated over Tonga on June 12. 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.

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

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 (14.1 inches). The largest single day rainfall in June 2006 was 63 mm (2.48 inches) on June 9 and 72 mm (2.83 inches) on June 30, 2006.

Featured image: Catholic Cathedral lake - Nuku’alofa, Tonga on June 11, 2016. Credit: Matangi Tonga Online

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