An increase in rainfall is expected in Kelantan, Terengganu, Pahang and Johor from this month until December following the northeast monsoon season.

Science, Technology and Innovation Minister, Datuk Seri Wilfred Madius Tangau said the monsoon season which was expected to begin in the middle of this month and ending in March next year, could result in continuous rain for three to five days and causing floods.

"According to the weather forecast for this month, Kelantan and Terengganu are expected to have between 300mm and 900mm of rainfall while some areas in the two states and east Pahang and east Johor will have 400mm to 800mm of rainfall in December.

"The temperature is also expected to drop to about 28 to 32 degrees Celsius and this is influenced by the weather condition," he told Bernama recently.

Madius said, meanwhile the northern states of Perlis, Kedah, Penang and Perak were predicted to have lesser rainfall than the East Coast states in December.

"The other states in the peninsula as well as Sabah and Sarawak are expected to have normal distribution of rainfall this month and in December," he said.

On the La Nina phenomenon, Madius said based on international weather models, a neutral condition or weak La Nina season was forecasted to occur until early next year.

"However, the formation of La Nina is currently slower in pace and the probability of it becoming weak is between 55 and 70 per cent," he said.

The phenomenon manifests when the sea surface temperatures across the east and central Pacific Ocean become lower than usual, resulting in monsoons acting erratically, among which causing extremely heavy rainfall.

Meanwhile, climatologist and oceanographer Prof Dr Fredolin Tangang from Universiti Kebangsaan Malaysia, said the impact of La Nina on the country was hard to predict as its depended on the sea surface temperature.

"However, based on my studies, the La Nina of moderate and weak force will result in heavy rainfall in the East Coast states of the peninsula rather than a strong La Nina," he said.

According to Tangang, attention should be given to the occurrence of weak or moderate La Nina in these states, expected to happen in November and December, while for Sabah and Sarawak it was estimated to occur in January and February.

He said, heavy rainfall, especially in the East Coast during the monsoon season in November and December would not only be caused by the La Nina phenomenon but also by the cold surge and the Madden-Julian Oscillation (MJO) phenomenon.

He explained that the collision between the cold surge and MJO could intensify the humidity concentration and the convection process on the East Coast, resulting in rainfall.

"However, the extreme rain and floods of December 2014 was not caused by La Nina but the presence of a strong cold surge as well as its clash with the MJO phenomenon then," he commented.

MJO is a large-scale climate variability occurrence that is generated by changes in temperature at the Indian Ocean which influences the humidity of the atmosphere and moves from there to the Pacific Seas, across Malaysia and Indonesia.

When the MJO is in its third phase, with an extensive convection centre on the west of Sumatra, the amount of rainfall in the East Coast of the Malaysian peninsula could double on the average.

Tangang reminded that the most critical condition for the East Coast states would be if both the MJO third phase and the cold surge occur concurrently, increasing the amount of rain in several areas.

However, he said, the MJO phenomenon and cold surge could not be predicted earlier by a month or two by agencies like the APEC Climate Center (APCC) as they did not have accurate information of the phenomenon. -- BERNAMA