Hai Duong's Climate
Sitting between Hanoi and Hai Phong on the lower Thai Binh River, Hai Duong is classic Red River Delta country: flat paddies threaded by the Kinh Thay, Kinh Mon and Luoc rivers, with one hilly corner in the northeast where the Chi Linh hills and Kinh Mon's An Phu range rise above the plain. The climate is tropical monsoon with a genuinely cool winter, and the province collects about 2,072 mm of rain a year.
The wet half of the year
The rains run from April to October, opening with afternoon heat thunderstorms. June is the hottest month, with average highs of 33.7°C, and heatwaves can turn the waterlogged fields around Gia Loc and Tu Ky into a steam bath. September is the wettest month — roughly 409 mm spread across 24 rainy days — and it overlaps with typhoon season: storms landing over Hai Phong and Quang Ninh often push inland with driving rain and gusts. Low-lying land along the Thai Binh and Sat rivers floods easily, so farmers watch every storm bulletin.
Winter: north winds, drizzle and the delta damp
From November, surges of the northeast monsoon sweep down past the Luc Dau Giang river junction and the air turns dry, then cold. December is the coldest month, with average lows of just 13.9°C, and sharper cold snaps dip below 10°C — noticeably rawer at night on the Con Son and Phuong Hoang hillsides. Late winter brings days of fine drizzle under unbroken grey, and February–March ushers in the notorious "nom" damp, when floors sweat and laundry refuses to dry. The upside: this is when thousands of storks and herons winter at Chi Lang Nam Stork Island in Thanh Mien.
A farming calendar written by the weather
Thanh Ha lychees need the winter chill to set their flower buds before ripening in the May–June heat; an unusually mild winter can wreck the harvest in the orchards along the Huong River. In late autumn, when the first cool, dry northerly winds arrive, the brackish fields of Tu Ky erupt with ruoi — tidal ragworms harvested for only a few days around the high tides of the ninth and tenth lunar months. The dry winter season belongs to Duc Chinh carrots on the Thai Binh riverbanks and to the onion and garlic fields below An Phu mountain in Kinh Mon.
When to go and what to pack
October–November is the sweet spot: dry, mild and golden — ideal for climbing Con Son, visiting Kiep Bac temple or cycling through Thanh Ha's guava and lychee orchards. The spring festival at Con Son–Kiep Bac in the first lunar month is lively but usually drizzly, so bring grippy shoes and a light jacket. In summer pack sun protection and check typhoon bulletins from July to September; in winter layer up, and during the damp spell of February–March a room with a dehumidifying air-conditioner makes all the difference.