This guide describes Chittagong's historical climate, not a live 15-day forecast. Monthly averages help compare seasons but cannot predict an individual day. Forecast uncertainty generally increases with lead time and depends on the location and weather variable. See the current seven-day forecast for upcoming weather.
What is normal in Chittagong, month by month
| Month | Max | Min | Rain | Rain days |
|---|---|---|---|---|
| January | 24.3° | 15.3° | 6.8 mm | 1 |
| February | 26.9° | 17.5° | 14.3 mm | 1.9 |
| March | 30.1° | 21.7° | 49.7 mm | 4.6 |
| April | 31° | 24.8° | 102.8 mm | 9.8 |
| May | 30.6° | 25.8° | 290.4 mm | 20.6 |
| June | 29.4° | 25.9° | 513 mm | 27.1 |
| July | 28.8° | 25.6° | 542.9 mm | 29.6 |
| August | 29° | 25.5° | 447.9 mm | 29.3 |
| September | 29.3° | 25.3° | 345.4 mm | 26.3 |
| October | 29.4° | 24.3° | 192 mm | 16.9 |
| November | 27.7° | 20.7° | 44 mm | 3.2 |
| December | 25.1° | 16.9° | 13 mm | 1.3 |
72% of Chittagong's 2562 mm falls between June and September, so during those four months a 15-day view is useful for spotting when the next wet spell is due, not for how much rain falls on a given day. The dry half of the year is not completely dry here: 22 rain days and 231 mm between November and April, enough that a two-week view is still worth checking for rain outside the monsoon.
How much a fortnight can tell you in Chittagong
The wet season builds here rather than breaking. July carries about 1.9 times the rain of May - a real increase, but a gradual one - so a fortnight's view is genuinely about how much and when, not simply whether the season has started.
The other thing worth knowing before reading a two-week forecast here is how far the year swings: 15.7°C between the hottest monthly average maximum and the coldest average minimum. The fastest change is into March, when the average daily maximum moves 3.2°C in a single month - and a forecast crossing that point is doing more work than one in a settled month.
The biggest turn in the year
Bangladesh Meteorological Department — BMD places the normal onset of the southwest monsoon over Bangladesh in the first week of June. The southeast coast, which includes Chittagong, is the first part of the country the monsoon reaches, typically in the last days of May or the first days of June. If you are looking at a 15-day outlook in late May, that is the real question you are asking.
We do not publish a calculated monsoon onset date for Chittagong, and the reason is worth stating plainly. Our method looks for the first sustained wet spell after 1 May. In most of South Asia that spell is the monsoon. In Chittagong it often is not: the pre-monsoon Kal Baisakhi thunderstorm season brings heavy, repeated rain through April and May that satisfies the same test. Applied to the 34-year record the method returns no usable answer in 10 of those years, and in the other 24 it returns dates that run two weeks earlier than the official normal. A rule that fails a third of the time is not measuring what it claims to measure, so we report the official figure instead.
The other turn is heat: April averages a daily maximum of 31°C, and that falls by 2.2°C once the monsoon is established.
When the monsoon reaches Chittagong — the full record
Sources
Source: Open-Meteo's historical weather archive, whose default model blends ERA5 and ERA5-Land reanalysis with ECMWF IFS HRES from 2017 — 1991-2024 (34 years). Open-Meteo offers no rainfall from ERA5-Land, so the rain figures come from ERA5 and IFS. Temperatures are monthly averages of daily highs and lows; rainfall is the average monthly total. A grid estimate can differ from a local weather station.
The live forecast for Chittagong is on a separate page and comes from Open-Meteo, which is built on ECMWF and other models.