East Asia Week 1 Weather Outlook
Rainfall, convection, surface winds, East Asian trough movement and South China Sea moisture transport for 16–23 July 2026.
Seven-Day Pattern Summary
The most important Week 1 feature is a broad low-pressure trough extending across the northern South China Sea and the coast of southern China. South-to-southwest winds feed warm, humid air toward Guangdong and Hong Kong, maintaining showers and thunderstorms through the weekend and into early next week.
Farther east, summer heating and high humidity support daily convection over the Philippines, eastern China, Korea and Japan. Rain becomes more locally organised where weak pressure minima, sea-breeze boundaries and upper-air disturbances intersect.
By roughly 21–23 July, the broad trough weakens and higher pressure aloft expands over southern China. Hong Kong and parts of southeastern China become hotter with fewer widespread showers, although isolated heat-triggered storms remain possible.
Where Rainfall Is Most Likely
Southern China and Hong Kong
Highest confidence for repeated showers and thunderstorms from 16–20 July. Heavy bursts are possible along the Guangdong coast while the broad trough and southwest flow remain aligned.
Western and Northern Luzon
Monsoon-fed showers favour western sections and extreme northern Luzon. Elsewhere, rainfall is more intermittent and driven by daily heating and local convergence.
Eastern China
Scattered rain and thunderstorms affect Fujian and nearby coastal provinces through about 20 July, followed by hotter and generally less widespread rainfall toward 22–23 July.
Korean Peninsula
A stronger rain episode is possible around 18 July, with heavy rain risk in places, followed by warmer and more humid weather and renewed local storms later.
Japan
Hot, humid and unstable conditions support repeated afternoon or evening thunderstorms, especially through 20–22 July. Rainfall placement will be locally variable.
Interior South and Southwest China
Strong rainfall remains possible over parts of Guangxi, Yunnan, the Sichuan Basin and adjoining zones, with local flash-flood and landslide risk.
Likelihood of Convection
Convection is most likely where three ingredients overlap: deep moisture, surface convergence and strong daytime heating. The broad trough supplies large-scale lift near southern China, while island and coastal heating creates smaller sea-breeze and terrain boundaries across the Philippines, Taiwan, Korea and Japan.
The greatest uncertainty is the exact location and timing of individual storm clusters. Under weak or moderate tropical winds, thunderstorms can organise rapidly along outflow boundaries that global models do not resolve precisely.
Surface Wind Pattern
| Region | Expected surface flow | Weather effect |
|---|---|---|
| Hong Kong / Guangdong coast | South to southwest, generally moderate and occasionally fresh offshore | Persistent marine moisture, morning rainbands, squally thunderstorms and rougher coastal waters early in the period |
| Philippines | Light to moderate south to southwest, locally south to southeast | Moist monsoon input in northern and western sections; local afternoon storms elsewhere |
| Fujian / southeast China | Mostly southerly or southwesterly, often light inland | Coastal showers plus strong daytime heating; local thunderstorm development |
| Korea | Variable humid flow around transient pressure systems | Rain episode near 18 July followed by hotter, humid conditions |
| Japan | Humid southerly background flow with local sea breezes | Heat, high humidity and repeated afternoon convection |
Yangtze River Basin: Full-Corridor Weather Pattern
The Yangtze forecast is best understood as a west-to-east chain rather than one uniform rain zone. The upper basin reacts strongly to terrain and plateau-edge disturbances; the middle reaches respond to converging monsoon moisture and the subtropical ridge boundary; and the lower reaches are sensitive to the East Asian trough, the Meiyu-style frontal zone and humid inflow from the East China Sea.
Upper Yangtze
Core areas: eastern Sichuan, Chongqing, western Hubei and the Three Gorges headwaters.
Most favourable for terrain-enhanced rain and repeated nocturnal convection. Local heavy totals are possible where southwesterly moisture rises against the Sichuan Basin rim and surrounding mountains.
Middle Yangtze
Core areas: Hubei, northern Hunan, Jiangxi and western Anhui.
Rainfall is more banded and convergence-driven. Thunderstorm clusters may form along the northern edge of the subtropical high and migrate eastward with short-wave troughs.
Lower Yangtze and Delta
Core areas: eastern Anhui, Jiangsu, Shanghai and northern Zhejiang.
Early-period showers and thunderstorms are possible, followed by a stronger trend toward heat, humidity and more isolated afternoon convection as the ridge expands late in the period.
Yangtze Daily Rain, Wind and Convection Outlook
The amounts below are indicative basin-sector ranges derived from the combined ECMWF/GFS/Chinese operational pattern, not point forecasts. Local thunderstorms can exceed the listed area-average range.
| Date | Upper Yangtze | Middle Yangtze | Lower Yangtze / Delta | Surface wind and convection |
|---|---|---|---|---|
| 16 Jul | 10–35 mm; local 50+ mm | 5–25 mm; scattered heavier cells | 5–20 mm, locally stormy | Light S–SW flow; high afternoon/evening convection inland |
| 17 Jul | 15–45 mm; terrain-enhanced | 10–35 mm; organised clusters possible | 5–20 mm; humid thunderstorms | Moist SW inflow strengthens slightly; nocturnal upper-basin storms |
| 18 Jul | 10–30 mm | 15–45 mm; local heavy rain | 10–30 mm; thunderstorm bands possible | Convergence axis shifts east; moderate convective risk throughout corridor |
| 19 Jul | 5–25 mm | 10–35 mm | 10–30 mm, locally higher | Light variable to southerly winds; storms focus near boundaries and urban heat zones |
| 20 Jul | 5–20 mm | 5–25 mm | 5–20 mm | Broad rain begins easing; isolated strong convection remains possible |
| 21 Jul | 5–20 mm, mainly terrain storms | 5–15 mm, scattered | 0–10 mm, increasingly hot | Subtropical ridge expands; lighter winds and stronger thermal convection |
| 22–23 Jul | 5–20 mm, local mountain storms | 0–15 mm, isolated storms | 0–10 mm; mainly isolated afternoon storms | Hotter, more stable aloft in east; weak winds increase local sea-breeze/urban effects |
Expected rainfall trend
Convection trend
East Asian Trough (EAT): Movement and Intensity
The EAT is expected to remain an important organising feature during the first several days. Its southern extension interacts with the broad trough over southern China and the northern South China Sea, helping focus moisture and ascent from Guangdong toward the western Pacific subtropics. Farther north and west, short-wave energy travelling around the EAT helps organise rain bands from the Sichuan Basin through Hubei, Anhui and the lower Yangtze.
Early in the period, the trough is more effective because low-level southwesterlies continue to feed it. This supports repeated upper- and middle-basin convective episodes and intermittent lower-basin thunderstorms. Around 20–22 July, the southern portion weakens as an anticyclone aloft gradually expands over Guangdong and eastern China. This reduces broad ascent and shifts the Yangtze corridor from organised rain bands toward hotter weather with more isolated, heat-driven convection.
South China Sea Moisture Input toward Hong Kong
The northern South China Sea acts as the principal moisture reservoir. South and southwest winds transport warm humid air toward the Pearl River Estuary. When this air meets the coastal trough, terrain and thunderstorm outflows, it rises rapidly and can produce heavy short-duration rainfall.
Hong Kong’s official forecast keeps south-to-southwest winds through 21 July, with occasional showers and thunderstorms, before winds become more southerly and the weather turns sunnier and hotter on 22–23 July.
Daily Sequence: 16–23 July 2026
Regional Outlook
Wettest early; showers ease by mid-to-late week. Very hot by 23 July.
Daily thunderstorms, with western and northern Luzon more exposed to monsoon moisture.
Heat plus scattered storms; Fujian wetter through about 20 July.
Rain episode around 18 July, then warmer and humid with renewed storms later.
Hot, humid and repeatedly unstable; afternoon storms remain common.
Humid and convectively active, especially terrain and afternoon-favoured districts.
Persistent warm-moist source region feeding southern China and the Philippines.
Locally heavy rain and terrain-enhanced flood or landslide risk.
Other Influences on the Yangtze and East Asia Pattern
Subtropical western Pacific high
Its western and northern edge helps define the rain-band position. A stronger westward ridge pushes organised rainfall north or west; a retreat allows troughing and convection to spread eastward.
Plateau and Sichuan terrain
Night-time low-level jets and uplift along the basin rim favour nocturnal storms and locally enhanced rain in the upper Yangtze.
Southwest monsoon moisture
Moisture entering from the Bay of Bengal and South China Sea feeds the upper and middle basin through Yunnan, Guizhou and southern China.
East China Sea inflow
Humid southerly flow can reinforce lower-Yangtze dew points, night-time storms and coastal convergence near Jiangsu, Shanghai and Zhejiang.
Summer heat
When organised rain weakens after 20–21 July, strong surface heating raises instability and supports isolated severe thunderstorms despite lower basin-wide totals.
Residual tropical disturbances
Any remnant low or tropical wave moving inland can locally rearrange the rain band and create totals far above the broader model average.
Why the rating is 4 out of 5
The broad trough, southwesterly moisture feed and early-period rainfall signal are well supported by official forecasts. Confidence is lower for the exact placement and timing of individual convective storms, particularly after Day 4–5 and in weak-wind island environments.