Wet start to the week, windy midweek, then sun
Thunder Bay residents should expect a damp, humid start to the week, with showers and a risk of thunderstorms through Tuesday morning before a sharp increase in wind later in the day. Environment Canada observations at 6:00 a.m. EDT Tuesday recorded light rain and a temperature of 17.3°C at Thunder Bay Airport, with humidity at 100%, barometric pressure falling at 101.7 kPa and visibility around 16 kilometres.
Forecasters warn of locally significant rainfall and strengthening winds as the system moves through. Showers are expected to taper off early Tuesday afternoon, but isolated thunderstorms are possible and some neighbourhoods could see 20 to 30 mm of rain. South winds will pick up to 20 km/h with gusts near 40 km/h.
Why it matters locally
That amount of rain in a short period can produce puddling on low-lying streets and slow drainage in areas with limited sewers. The strong gusts later Tuesday and the more significant wind event forecast for Wednesday — when gusts may reach 60 km/h — raise the risk of small branches downed, unsecured outdoor objects being displaced and more challenging driving conditions for high-profile vehicles.
| Day | High | Low | Winds (gusts) |
|---|---|---|---|
| Tuesday, Sept. 8 | 21°C | 14°C | South 20 km/h (gusts to 40 km/h) |
| Wednesday, Sept. 9 | 20°C | 7°C | West 40 km/h (gusts to 60 km/h) |
| Thursday, Sept. 10 | 21°C | Near 10°C | Light |
Timing and expectations
Tuesday: Showers continue through the morning and are expected to end by early afternoon. There is a risk of a thunderstorm during the morning. The humidex may push the perceived temperature to about 28 on the warmest hours of the day. Tuesday night will remain mainly cloudy with a 30 percent chance of additional showers and an evening thunderstorm risk.
Wednesday will be the windiest day of the short-range forecast. West winds are forecast to strengthen during the morning from about 20 km/h gusting to 40 km/h, then increase to sustained values near 40 km/h with gusts up to 60 km/h. Skies will be mainly cloudy with a 40 percent chance of showers late in the morning and afternoon. Temperatures will fall markedly, with a Wednesday night low near 7°C.
Thursday brings a clear improvement. Environment Canada is forecasting plenty of sunshine and a high back into the low 20s, around 21°C, as the cooler, drier air firmly settles over the region.
Local preparedness — practical steps
- Secure loose patio furniture, garbage cans and other lightweight items before Wednesday when gusts are expected to be strongest.
- Allow extra travel time on Tuesday morning for standing water and reduced visibility in heavy downpours; be cautious of hydroplaning.
- If you live near rivers or low-lying areas, monitor local drainage and municipal advisories — 20–30 mm falling quickly can overwhelm small drains.
- Those with outdoor plans later in the week should consider rescheduling to Thursday when sun and calmer conditions are expected.
Residents should monitor updates from Environment Canada and local municipal services in case showers intensify or wind warnings are issued. The weather will shift quickly over the next 48 hours — from humid and unsettled to brisk and clear — a reminder of how transitional September can be in Northwestern Ontario.
