Why it so often rains during Bangkok's evening rush-hour

Why it so often rains during Bangkok's evening rush-hour

Motorists on Tri Petch Road fight floodwater after a downpour in Bangkok on Friday. (Photo by Apichart Jinakul)
Motorists on Tri Petch Road fight floodwater after a downpour in Bangkok on Friday. (Photo by Apichart Jinakul)

Ever wonder why rain always seems to hit Bangkok just when you are about to go home after work? The Meteorological Department has an explanation.

Department official Wuttipong Nubanjong on Monday said clouds that produce rain gather strength from moisture and sunlight over the Andaman Sea in the morning. They grow bigger as the southwesterly winds in the rainy season blow them to the mainland.

Rain normally starts in western provinces including Ratchaburi and Phetchaburi early in the afternoon. When they move further inland they accumulate more moisture along the path, the official explained.

By the time the rainclouds reach Bangkok, it is late afternoon in the capital, he said, adding accumulated moisture sometimes turned into downpours.

"Bangkok is in the path of the southwesterly wind," Mr Wuttipong said. "It's a pattern in the rainy season."

How soon rain hits Bangkok depends on wind speeds, according to the official. "A faster speed means rain in the afternoon from 3pm and a slower speed means rain in the evening," he said. 

Bangkok was flooded on Friday after a two-hour downpour in the afternoon. It paralysed traffic in the capital and commuters had to wait for hours for public transport to go home.

Suffering commuters directed their anger at Bangkok governor Aswin Kwanmuang, blaming him for poor preparations of flood-prevention measures.

The governor posted a Facebook message on Saturday apologising to people for the "inconvenience" but said he was working with his staff at the Bangkok Metropolitan Administration's command centre to drain floodwaters from Bangkok streets.

"Why wasn't I more hands-on, going out on the streets [to direct workers to drain floodwater]? Allow me to explain. I decided to follow the situation at the centre so I could get the big picture and better solve the problem," he said.

The rainy season this year officially began on May 20.

The weather agency on Monday predicted rain and heavy rain in Bangkok on Monday and Tuesday, again between the late afternoon and early evening.

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