Bangkok Seasonal Weather Outlook Aero Light Weather Analysis
Summary
Bangkok and central Thailand move into the dry northeast monsoon season from November 2025 through January 2026. This is the period when the South China Sea and Indo–China region come under the influence of cool, dry continental air masses from the north, replacing the humid southwest monsoon of mid-year. However, some irregular weather activity may still appear in early November and occasionally during MJO pulses or rare tropical systems tracking from the South China Sea. Overall, conditions trend drier, cooler, and more stable toward December and January.
1. Transition to Drier Monsoon Conditions
By early November, Bangkok begins transitioning from the retreating southwest monsoon to the northeast monsoon regime. Winds gradually shift from variable southwesterlies to steady northeasterlies, bringing in cooler, drier air from the Chinese mainland. Rainfall decreases sharply after mid-November, with clearer skies and lower humidity dominating by December. The dry period peaks in January when continental high pressure extends southward, keeping Bangkok mostly rain-free.
The reduction in convection and rainfall is aided by reduced sea surface temperatures in the Gulf of Thailand and reduced moisture inflow from the west. Nevertheless, occasional moisture incursions can bring brief cloudy or drizzly periods.
2. Cooling of the Himalayas and Its Northern Influence
As the Himalayas and northern Asian interior cool rapidly in late 2025, strong high-pressure systems form over northern China. These air masses push cool, dry air southward into mainland Southeast Asia, strengthening the northeast monsoon winds. Bangkok often experiences cooler mornings (18–22°C) and lower humidity during this period. The continental outflow also suppresses convection over the central plains, reinforcing the dry spell.
When strong surges of cold air descend, they can produce gusty northeasterly winds, lower nighttime temperatures, and rougher seas in the Gulf of Thailand. These surges may also create short-lived rainfall along the east coast of Thailand (Chumphon, Surat Thani, Nakhon Si Thammarat) but usually leave Bangkok dry.
3. Interaction from the Eastern Peninsula and South China Sea
The east side of the Thai–Malay Peninsula remains wetter than Bangkok during this period. When the northeast monsoon winds cross the Gulf of Thailand, they pick up moisture and release it as rainfall along the eastern slopes. Occasionally, moisture or thunderstorm clusters from this region can push inland and bring isolated light rain to central Thailand, especially in November.
Rare strong storms or tropical depressions forming over the South China Sea may curve west or northwestward across southern Vietnam or the Gulf of Thailand in early winter. If these occur, they can deliver brief heavy rain and gusty winds to Bangkok. However, under the expected weak La Niña and a strengthening subtropical high, the likelihood of such storms remains low but not zero in November; it decreases sharply by December.
4. Southern Influences — Weak La Niña and MJO Pulses
The forecast weak La Niña tends to enhance convection near the Maritime Continent and southern parts of Thailand. For Bangkok, this means slightly above-normal humidity in November but generally dry conditions afterward. If an active MJO (Madden–Julian Oscillation) pulse moves into the Maritime Continent phase (phases 4–6) during November–January, short-term rainfall spikes could occur, especially in early December.
Such MJO events can briefly reverse the dry trend, producing cloudiness or scattered showers over central Thailand. Still, these episodes usually last only a few days before conditions return to clear and dry.
5. Practical Advice for Bangkok Residents
- Comfort: Expect cooler mornings and evenings; a light jacket may be useful from late November through January.
- Rain planning: By mid-November, outdoor activities are generally safe from heavy rain; early November still has some thunderstorm risk.
- Air quality: As the monsoon weakens, temperature inversions may trap pollutants—air quality monitoring becomes more important from December onward.
- Travel & marine: Rough seas possible in the Gulf of Thailand during cold-air surges; avoid small craft operations during such events.
- Storm vigilance: Monitor forecasts in early November for rare tropical systems tracking from the South China Sea.