The ‘freak storm’ that wreaked havoc on Penang

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KINIGUIDE | From the late night of Nov 4 into the wee hours of Nov 5, the northwestern region of Peninsular Malaysia, including Penang and Kedah, was lashed by strong winds and unrelenting rain.

At around the same time, Typhoon Damrey slammed into Vietnam, killing at least 61 people.

Penang experienced its heaviest rainfall in recorded history, 315mm in a single day, according to the Penang Water Supply Corporation.

Devastating floods in Penang and parts of Kedah followed.

Malaysiakini puts this unusual weather event into context for this edition of KiniGuide.

Was the violent weather because of Typhoon Damrey?

No. Typhoon Damrey did not hit Penang. Damrey was a full-fledged typhoon. What hit the northwestern peninsula was a “tropical disturbance” referred to as “Invest 95W”.

What's the difference between a tropical disturbance and a typhoon?

A tropical disturbance is the very beginning of a possible typhoon. A tropical disturbance can progress into a tropical depression, then a tropical storm and finally - for this region - a typhoon.

The final stage is referred to as a hurricane in the North Atlantic Ocean and Northeast Pacific or a cyclone in the South Pacific and the Indian Ocean.

A tropical disturbance is an area of low pressure that brings with it clouds and rain. The US National Oceanic and Atmospheric Administration (NOAA) defines it as a discrete tropical weather system with an organised convection that is 200 to 600 kilometres in diameter.

According to the NOAA, if it gathers strength to a sustained wind speed of 20 to 33 knots (37 to 61km/h), it will be upgraded to a tropical depression and if it attains a sustained wind speed of 34 to 63 knots (63 to 117km/h) it is again upgraded to a tropical storm.

Sustained wind of 64 (118km/h) knots and above means, it has developed into a typhoon.

So how did the tropical disturbance over Penang develop?

At the end of October, meteorology enthusiasts have been observing two tropical disturbances that had developed - one over the Spratly Islands, west of the Philippines, referred to as “Invest 95W”, another called "Invest 96W" in the east of the Philippines...