Weather in United States in September

September climate overview

Daytime highs across United States in September run from 23.7°C (New York) to 33.6°C (Las Vegas). In Las Vegas about 98% of September days reach 25°C. Nights average 22.4°C; the coldest 10% of nights in New York fall to 11°C or below.

Rainfall in September

Expect around 13 rainy days (1 mm or more) in September, with Las Vegas the driest (1 days) and Miami the wettest (22 days). The wettest September at Las Vegas between 1991 and 2020 was 1997 with 53 mm; the driest was 1994 with 0 mm.

Sea temperature

The sea averages 26.7°C around United States in September - warmest at Florida (29.3°C). That is comfortable for swimming.

Sunshine and daylight

Around 6.1 hours of sunshine a day on average, out of 12.2 hours of daylight (sunshine estimated from cloud cover).

September against the rest of the year in United States

September is the 4th warmest month of the twelve in United States. It is 1.9°C cooler than August and 3.3°C cooler in October. The hottest month here is July (31°C) and the coolest January (18°C).

Which part of United States in September?

• Most sunshine: Las Vegas, 10.3 h a day.
• Driest: Las Vegas, about 1 rainy days.
• Warmest sea: Florida, 29°C.
• Hottest: Las Vegas, 34°C by day - intense for sightseeing.
• Coolest (better for walking and cities): New York, 24°C.

What to pack for United States in September

Based on the averages: summer clothes for the day; a rain jacket - roughly 13 wet days; swimwear - the sea is 27°C.

Similar weather elsewhere in September

Within 1.5°C of United States's September daytime average: Seville (30°C), Limassol (30°C, sea 27°C), Puerto Vallarta (30°C, sea 30°C), Ho Chi Minh City (30°C), Antalya (30°C, sea 28°C). See the full ranking for September.

Las Vegas for dry heat, New York for milder days

Las Vegas is the hottest option here at 34°C by day, with just 1 rainy day. That makes it a strong choice if avoiding rain matters most, but the heat is the trade-off: plan outdoor time around the cooler parts of the day and leave room for breaks at midday. Nights average 21°C, so evenings offer some relief. New York is a better fit if you prefer walking around without such intense heat. Its 24°C days give way to 16°C nights, making a light layer useful after dark. With 9 rainy days, keep plans flexible rather than expecting an entirely dry city break.

Florida is warm, but rain is a real consideration

Florida suits travellers who value warm water more than reliably dry days. The sea averages 29°C, while daytime temperatures reach 30°C and nights stay at 24°C. The catch is 20 rainy days, so leave flexibility for indoor time rather than building every day around being outside. Orlando has similar daytime heat at 30°C, with 19 rainy days and 23°C nights. Miami is slightly less hot by day at 29°C, but its 26°C nights offer less cooling after sunset, and 22 rainy days make rain a frequent consideration. Pack light clothing and rain protection; this is not the strongest choice for avoiding wet weather.

Hawaii offers a balance of warmth and fewer rainy days

Hawaii is a good fit if you want warm days and sea swimming without Florida's frequency of rain. Daytime temperatures average 28°C, nights remain warm at 24°C, and the sea is 27°C. With 7 rainy days, it offers a more favourable balance for outdoor plans, though you should still allow for wet weather. Light clothing should cover most warm-weather needs, with rain protection handy when heading out. Compared with Las Vegas, the daytime heat is less intense; compared with New York, evenings and the sea are warmer. It suits travellers who want warmth to continue after sunset rather than a noticeably cooler end to the day.