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The amount of rain that fell from October 6 to 13 was two to six times higher than normal.
Ha Tinh Province received 150-400 mm during this period, Quang Binh got 400-500 mm, Quang Tri got 800-1,500 mm, Thua Thien Hue got 1,300-2,000 mm, Da Nang City got 1,100 mm, Quang Nam got 900-1,200 mm, and Quang Ngai got 600-800 mm.
Rainfall of 180 mm a day is considered heavy.
The entire central region suffered from severe flooding for days, more than 135,000 houses were submerged under 0.3-4 meters of water, and nearly 46,000 people had to be evacuated.
At least 36 people have died due to flooding and 12 are missing.
Nguyen Van Huong, head of the National Center for Hydro-Meteorological Forecasting’s Climate Forecast Office, said intertropical convergence zone stretches from the Bay of Bengal and across the center of Vietnam to the Philippines.
In these areas clouds and thunderstorms often develop, and when winds from the east meet them, there is an increase in moisture content, which means more thunderstorms, he said.
When the zone has favorable conditions such as the convergence of strong winds that moved over warm seawater, a tropical depression forms and then grows into a storm in the East Sea, also known as the South China Sea, he said.
Since October 6 two storms and a tropical depression have formed in this area.
On Sunday Storm Linfa intensified from a tropical depression and made landfall over Quang Nam and Quang Ngai.
A day later Storm Nangka formed and hit the coast between the northern Thai Binh and central Thanh Hoa Provinces on Wednesday.
"Storms and tropical depression already cause heavy rains. For instance, Storm Linfa caused rainfall of 500-700 mm," Huong said.
On Thursday morning another tropical depression formed over the sea and is heading straight for the central region also with a lot of moisture.
According to the center, more rains are expected in the region until Tuesday or later.
A cold spell coming down from the north and meeting winds from the east also caused heavy rains, Huong said.
The center said the root cause of all these phenomena was La Nina, which appeared in July and is expected to last until early next year. During this period, more storms would form over the East Sea and the rains would last longer than usual, it added.
Four to six more storms and tropical depressions are expected to brew this year with at least two making landfall over the central coast.
La Nina is a complex weather pattern that occurs every few years as a result of variations in ocean temperatures in the Equatorial Pacific. It occurs as strong winds blow warm water on the ocean's surface from South America across the Pacific Ocean toward Indonesia.
Natural disasters, mostly floods and landslides triggered by storms, killed 132 people and injured 207 last year.
Flood zone communities adapt to life with floods. Video by Hoang Tao, Anh Phu.
