"Kalmaegi" intensifies as it heads toward Thailand, adding to the flood risk from heavy rains and La Niña

Chawalit Chantharat, Chief Executive Officer of Team Consulting Engineering and Management (Team Group), a water management expert, gave an exclusive interview to Bangkok Business about the complicated and concerning weather and flood situation. He pointed out two overlapping abnormal factors that are making the storm a more severe threat than originally predicted, with continued impacts on the central region.

Chawalit analyzed that the unusual heavy rainfall in several areas resulted from different atmospheric mechanisms:

• Northern Thailand (Chiang Mai-Sukhothai): This was caused by the direct clash between cold air from China and warm, moist air from the Andaman Sea, resulting in 2-3 days of heavy rain, expected to clear by November 4.
• Central Thailand (Bangkok and surrounding areas): This was caused by the phenomenon of "retreating cold winds" (where cold air weakens and retreats), which pulled the monsoon trough upwards from Phetchaburi, passing over Bangkok and the surrounding areas, leading to three days of heavy rain (November 1-3), due to massive moisture drawn from the Gulf of Thailand.

Typhoon Kalmaegi, the 25th storm of the year, is expected to intensify into a Category 3 typhoon as it makes landfall in Vietnam on November 6. Afterward, it will weaken into a tropical storm and move into Thailand, affecting areas like Ubon Ratchathani, Sisaket, and Yasothon on November 7, before dissipating around Khon Kaen on November 8-9.

Chawalit identified two main contributing factors for the intensified impact of Kalmaegi:

1. Excessive retreat of cold winds: The retreat of cold air from China, which usually acts as a "barrier," has created an opening for the storm to penetrate deep into northeastern Thailand, reaching as far as Khon Kaen.
2. La Niña influence: The onset of La Niña in November has strengthened the trade winds, making the storm more powerful and enabling it to retain its strength as it moves inland.

The influence of Kalmaegi will have the most severe effects in two main regions:

1. Northeastern Thailand: In areas along the Chi-Mun River Basin, the water levels are expected to exceed the riverbanks. Water will also reach the full capacity of reservoirs by November 9, including the areas around Ubolratana Dam (Khon Kaen), Lampao Dam (Kalasin), and along the Chi River (Maha Sarakham, Roi Et, Yasothon, Ubon Ratchathani).
2. Central Thailand: The water levels will rise again in areas downstream of the Chao Phraya River, especially in Bang Ban District, Sena District, and Phak Hai District in Phra Nakhon Si Ayutthaya. Increased water release from Chao Phraya Dam is expected to raise water levels by around 30 cm in these areas.

Chawalit emphasized that while Kalmaegi will help fill reservoirs in the lower northeastern region, the risk of severe flooding in downstream and riverside areas remains high. He urged people in these regions to prepare for possible disasters closely. Although Kalmaegi is the 25th storm this year, it is typical to have around 30 storms annually. Therefore, there is still a likelihood of up to five more storms before the end of the year, which could follow the monsoon trough into southern Thailand, potentially causing continuous heavy rainfall and flooding in the southern regions as well.