Meanwhile, Storm Koto, the 15th tropical storm of the year, is weakening faster than expected and is likely to turn into a low-pressure system before hitting the South Central Coast.
According to the Southern Regional Hydrometeorological Center, a weak easterly cold air system has returned but is expected to strengthen again from the night of December 2 and around December 7.
Storm Koto has been moving westward over the central South China Sea, shifting southwest and then west-southwest before gradually weakening into a low-pressure system heading toward the mainland.
Storm Koto nearly stationary, expected to weaken further
As of 10 a.m. on December 1, Vietnam's National Center for Hydro-Meteorological Forecasting reported the storm's center over the northwest area of the central South China Sea. Winds near the center reached 62-74 km/h (level 8), gusting to level 10.
The storm showed little movement during this time.
Over the next 24 hours, it is expected to drift southwest at about 5 km/h, downgrading into a tropical depression. By 10 a.m. on December 2, its center will likely be located 170 km east of the Gia Lai-Dak Lak coastline, with wind speeds down to level 6 and gusts to level 8.
In the following 12 hours, the tropical depression is expected to continue moving southwest at 10 km/h, weakening into a low-pressure system near the Gia Lai-Khanh Hoa coast.
This means that Storm Koto will transform into a tropical depression and then a low-pressure zone between tonight and midday tomorrow - earlier than initially forecast.
Rainfall forecast for central and southern provinces
Due to the storm's circulation combined with other weather patterns, moderate to heavy rain is expected from Quang Ngai to Dak Lak and Khanh Hoa between the night of December 2 and the end of December 3. Rainfall will average 70-120mm, with some areas receiving over 180mm.
From December 3 to 5, areas from Quang Tri to Da Nang and eastern Quang Ngai may see 50-150mm, with localized totals exceeding 250mm.
Heavy rainfall exceeding 100mm in 3 hours may lead to urban flooding, flash floods in small rivers and streams, and landslides on steep slopes.
10-day national weather outlook (Nov 30 - Dec 10)
November 30 - December 2: In the North and North Central regions: Light rain at night, fog in some areas early morning, followed by sunshine during the day. Cold mornings and evenings, with possible frost or freezing in high mountains.
Elsewhere: Isolated showers and thunderstorms. From December 2, expect scattered rain and storms in South Central Coast, Central Highlands, and Southern Vietnam. The Central Highlands will be chilly at night and early morning; other areas will be cool.
December 2-10: In northern provinces and Thanh Hoa, Nghe An: Scattered showers expected on Dec 2-3 and Dec 7-8. Cold mornings and evenings. From Dec 3, temperatures will drop further, especially in mountainous areas.
In Ha Tinh to Hue: Moderate to heavy rain expected from Dec 3-5, followed by scattered rain. Some areas may experience localized downpours.
In the South Central Coast: Moderate to heavy rain likely from Dec 2-4, especially in northern parts.
In the Central Highlands: Rain and thunderstorms expected from Dec 2-4, with isolated heavy rain. Later in the period, scattered showers.
In Southern Vietnam: Scattered showers and thunderstorms from Dec 2-4, easing into localized showers afterward.
Across all regions, thunderstorms may bring tornadoes, lightning, hail, and strong winds.