Weather statistics are here -

Varna

Bourgas

But the answer to your weather question is "who knows?"

Particularly in these times of climate change.

Based on our experience over many years it should be quite to very warm, could even be hot - you should get a tan, but you might have some rainy days.

Towards the end of September, some things might be starting to close down, especially if the weather isn't that good.

Good luck, it's probably around the time we will be there because we don't like it too hot!

Peter

Golden Sands/Varna is quite cold during September , I wouldn't go.
Better try Sunny Beach.

Sorry Marti, the statistics do not support Golden Sands/Varna being quite cold in September, whilst Sunny Beach is warmer.

The difference is precisely one degree Celsius with respect to both maximum and minimum average temperatures. Click on the links above and see.

Guess what, Varna comes up warmer!!

I don't call an average max temperature for Varna of 26, and a min of 14, 'quite cold'.

More a case of "How do you operate this air conditioner?"

Peter

You may watch the forecast and compare it through internet but actually it is more windy there, more rain , the sea water is always colder than the South .......I'm not saying that in Sunny Beach the weather is perfect but more South you go better it is.
IF you like using the swimming pool rather than going to the beach there is no much difference where you'll go.

IF you prefer the beach one of the best places is Sinemorec.

There are many reasons to prefer one resort over the other, but the weather isn't one of them, as the statistics plus our own experiences prove.

As for it being colder the further North you go, one of the hottest places I have been to in any country in the world is the delightful Bulgarian city of Russe.

You can't get much further North than that and not be in Romania - it's on the Danube.

One September I proceeded along the main pedestrian precinct at a rate of two bottles or cans of Coke or Fanta per 50 metres, it was that debilitatingly hot!

Peter

Hi, Can confirm that the weather in SB and GS at that time of year is about the same. We always go September and on the whole have no complaints. Plenty of hot/warm days, some torrential downpours(usually lasting a day) and the nights are quite cool/chilly enough for a jumper.
we always come back well tanned.
Look on the bright side, anything is better than the UK in late September.

The Toonman