The Black Sea · daily temperatures 1982–2026
Swimming days on the Black Sea, 1982–2026: how long the season lasts at each resort
From Sulina, at the Danube's mouth, to Varna in Bulgaria, the sea now stays at 20 °C or more for three to four weeks longer each year than in the 1980s: between 21 and 28 extra swimming days on every stretch of coast. At Mamaia, Romania's largest Black Sea resort, the water reaches 20 °C or more on about 123 days a year, against 99 in 1982–1991. The season opens about 7 days earlier and closes about 8 days later.
The sea, day by day
The map shows the sea on a single day, coloured by its measured temperature; from 20 °C up the tones turn warm, and the white line separates cooler water from water warm enough to swim. Play a summer and watch the sea cross the line. In 1982–1991 the first swimming day at Mamaia came, on average, on 12 June; in 2016–2025 it comes on 5 June.
Mamaia: every summer, day by day
Map: surface water temperature on the chosen day, on satellite cells of 0.25 degrees, blended smoothly between their centres; the white line is the 20 °C threshold. The drawing of summers: each row is one year, each column one day from 1 April to 31 October, off the chosen resort; days at 20 °C or more are in warm tones. Blue patches in mid-summer are cooler days. The dotted square on the map is the satellite cell that gives the chosen resort its figures.
Your beach and your holiday week
Pick a resort from the list or press the map above, next to your resort. Then pick a day in your usual holiday week: the answer shows in how many summers of 1990–1999 the water was warm enough to swim that week, and in how many of 2016–2025.
days a year at 20 °C or more (2016–2025 mean)
days more than the 1982–1991 mean
The season has stretched at both ends
The first day at 20 °C or more reached Mamaia on 12 June in an average year of 1982–1991. In 2016–2025 it arrives on 5 June. The last swimming day of the year has moved from 30 September to 8 October. The same happened along the whole coast.
The same measure across the whole strip of sea: days a year with water at 20 °C or more, ten-year mean, for each satellite cell. The figures are the days off each stretch of coast. Along the whole coast, from Sulina to Varna, the sea has gained between 21 and 28 days a year; most off Corbu.
The swimming season, from the first to the last day at 20 °C or more
average season 1982–1991 average season 2016–2025
Resorts that share the same nearest satellite cell share a series and are grouped. Each resort takes the nearest cell whose centre lies at sea, at most 24 km from the resort.
Very warm water has become ordinary
At 20 °C most people get in without a long hesitation. At 24 °C getting in takes no courage at all. The 24 °C line tells the clearest story: at Mamaia the water crossed it on about 15 days a year in 1982–1991 and crosses it on about 61 days a year in 2016–2025. The June-to-September mean temperature off Mamaia has risen by 0.6 °C a decade.
| Resorts | Days a year at 20 °C or more, 1982–1991 | 20 °C or more, 2016–2025 | 22 °C or more, 2016–2025 | 24 °C or more, 1982–1991 | 24 °C or more, 2016–2025 |
|---|---|---|---|---|---|
| Sulina | 94 | 117 | 95 | 13 | 54 |
| Gura Portiței | 96 | 122 | 98 | 16 | 59 |
| Corbu | 95 | 123 | 97 | 15 | 59 |
| Mamaia – Eforie | 99 | 123 | 98 | 15 | 61 |
| Costinești – Neptun – Mangalia – Vama Veche | 100 | 124 | 98 | 16 | 63 |
| Shabla | 101 | 122 | 98 | 15 | 63 |
| Kavarna | 103 | 126 | 102 | 16 | 67 |
| Balchik – Albena – Golden Sands | 104 | 127 | 104 | 17 | 68 |
| Varna | 105 | 128 | 104 | 18 | 69 |
Ten-year means, rounded to whole days. The year-by-year count for Mamaia follows.
Days at 20 °C or more, year by year: Mamaia – Eforie
| Year | ≥20 °C | ≥22 °C | ≥24 °C | First day | Last day | Sudden drops |
|---|---|---|---|---|---|---|
| 1982 | 100 | 58 | 13 | 14 June | 5 October | 0 |
| 1983 | 106 | 65 | 8 | 26 May | 29 September | 0 |
| 1984 | 98 | 43 | 2 | 5 June | 11 October | 0 |
| 1985 | 80 | 37 | 0 | 5 June | 26 September | 0 |
| 1986 | 118 | 78 | 25 | 1 June | 26 September | 0 |
| 1987 | 98 | 47 | 4 | 25 June | 30 September | 0 |
| 1988 | 94 | 71 | 43 | 10 June | 25 September | 1 |
| 1989 | 90 | 71 | 17 | 26 June | 24 September | 0 |
| 1990 | 97 | 64 | 3 | 21 June | 27 September | 0 |
| 1991 | 108 | 56 | 35 | 16 June | 3 October | 0 |
| 1992 | 97 | 52 | 31 | 19 June | 23 September | 0 |
| 1993 | 97 | 36 | 1 | 13 June | 23 September | 0 |
| 1994 | 106 | 93 | 44 | 28 June | 11 October | 0 |
| 1995 | 112 | 94 | 45 | 4 June | 23 September | 0 |
| 1996 | 100 | 68 | 12 | 8 June | 17 September | 0 |
| 1997 | 91 | 53 | 3 | 15 June | 13 September | 0 |
| 1998 | 113 | 67 | 35 | 2 June | 22 September | 0 |
| 1999 | 125 | 83 | 47 | 1 June | 7 October | 0 |
| 2000 | 113 | 65 | 20 | 29 May | 24 September | 0 |
| 2001 | 103 | 82 | 54 | 25 June | 6 October | 0 |
| 2002 | 108 | 84 | 44 | 14 June | 29 September | 0 |
| 2003 | 112 | 77 | 31 | 4 June | 25 September | 0 |
| 2004 | 111 | 69 | 1 | 12 June | 3 October | 0 |
| 2005 | 118 | 74 | 46 | 1 June | 6 October | 0 |
| 2006 | 111 | 83 | 44 | 23 May | 7 October | 0 |
| 2007 | 120 | 91 | 50 | 8 June | 6 October | 0 |
| 2008 | 106 | 86 | 26 | 10 June | 23 September | 0 |
| 2009 | 124 | 72 | 31 | 8 June | 9 October | 0 |
| 2010 | 111 | 80 | 50 | 10 June | 29 September | 0 |
| 2011 | 125 | 90 | 23 | 24 May | 9 October | 1 |
| 2012 | 138 | 96 | 67 | 4 June | 19 October | 0 |
| 2013 | 112 | 89 | 46 | 20 May | 29 September | 1 |
| 2014 | 128 | 92 | 49 | 25 May | 3 October | 0 |
| 2015 | 123 | 101 | 50 | 1 June | 7 October | 0 |
| 2016 | 121 | 98 | 63 | 3 June | 7 October | 0 |
| 2017 | 119 | 95 | 35 | 5 June | 1 October | 0 |
| 2018 | 122 | 105 | 67 | 25 May | 2 October | 0 |
| 2019 | 129 | 105 | 75 | 1 June | 7 October | 0 |
| 2020 | 128 | 99 | 70 | 17 June | 22 October | 0 |
| 2021 | 109 | 91 | 59 | 10 June | 1 October | 0 |
| 2022 | 118 | 83 | 53 | 4 June | 2 October | 0 |
| 2023 | 133 | 103 | 44 | 2 June | 18 October | 0 |
| 2024 | 131 | 108 | 78 | 4 June | 12 October | 0 |
| 2025 | 119 | 95 | 65 | 7 June | 3 October | 0 |
| 2026 | 124 | 98 | 72 | 6 June | 12 October | 0 |
Sudden cold water: what the shore sees and the satellite misses
In mid-summer the water near the shore can lose several degrees from one day to the next. Wind pushes the warm surface layer out to sea and cold water rises from below to replace it. The process is called upwelling, and Romania's National Institute for Marine Research and Development "Grigore Antipa" in Constanța has measured it on this coast.
One example: in July 2017 an upwelling episode suddenly lowered the water near the East Constanța research profile to 10 °C, in mid-season, at the surface or at 10 metres (Tabarcea, PhD thesis, Institute of Biology of the Romanian Academy; the summary does not say which). That same month, the satellite cell off Corbu never fell below 22.4 °C, and the largest two-day fall in the cell off Mamaia and Eforie was 1.3 °C. The satellite series does not keep the episode.
Sudden drops are therefore counted here with care. The rule used — a fall of at least 3 °C within two days, between June and September, starting from water of at least 19 °C — finds only 26 episodes in the whole series, nine stretches of coast over 45 summers. The largest fall the satellite keeps: 5.1 °C within two days, off Sulina, starting on 26 June 2011. The blue patches in the drawing of summers show only offshore cooling; a cold week at the beach can hide inside a cell that stays warm.
How the days were counted
Daily temperatures come from the OISST series, version 2.1, produced by NOAA's National Centers for Environmental Information in the United States from satellite measurements blended with ship and buoy readings. The series covers every day from 1 January 1982 to 31 October 2026 on cells of 0.25 degrees, roughly 28 kilometres north to south and 20 kilometres east to west. The last two weeks are preliminary data; they change no figure here, because the last day at 20 °C or more in 2026 was 13 October.
Each resort takes the nearest cell whose centre lies at sea on the real shoreline from OpenStreetMap and whose series is complete; that centre lies at most 24 km from the resort. Resorts that share the same nearest cell share a series and are grouped in the tables. The map blends smoothly between cell centres; every figure in the text comes from the whole cell, not from the blending.
A swimming day is a day whose cell mean reaches at least 20 °C. The 22 °C and 24 °C lines stand beside it for readers with a different idea of comfort. Period figures are means over the whole years of each period. For a chosen week, the chance of swimmable water counts the years in which the water held at least 20 °C on five of the week's seven days (weeks are numbered by the calendar; the dates shown are those of 2025).
The series describes the top layer of the open sea, matched to ship and buoy readings from the first few metres, day and night together. The shallows at the beach, where people swim, warm further through a sunny day and can cool harder in an upwelling episode. The days counted here describe the water off each resort; at the shoreline the felt season can run a few days longer in calm summers and shorter in weeks when the wind pushes the surface water out to sea. Filling cloudy days by interpolation smooths sudden falls, so the count of sudden drops stays a minimum.
Two checks. The first years of the series have fewer satellite measurements; starting the reference period in 1984 instead of 1982 gives a gain of between 22 and 30 days per stretch of coast, so the gain does not shrink. For the whole Black Sea basin, Mohamed, Ibrahim and Nagy (2022, Remote Sensing) computed from daily satellite data at 0.05 degrees a warming of 0.65 ± 0.07 °C a decade, annual mean, between 1982 and 2020. Over the same years and on the same measure, the series used here gives between 0.49 and 0.53 °C a decade off each stretch of coast: the same direction, warming a little more slowly than the basin average.
Sources: NOAA NCEI, Optimum Interpolation Sea Surface Temperature (OISST) v2.1; Huang et al. (2021), "Improvements of the Daily Optimum Interpolation Sea Surface Temperature (DOISST) Version 2.1", Journal of Climate, doi:10.1175/JCLI-D-20-0166.1; Mohamed, Ibrahim & Nagy (2022), "Sea Surface Temperature Variability and Marine Heatwaves in the Black Sea", Remote Sensing 14, 2383, doi:10.3390/rs14102383; Mihailov et al. (2013), "Characteristics of up-welling, algal bloom and hypoxia events in the western Black Sea in 2010", Fresenius Environmental Bulletin 22 (10a), 2981–2990; C. Tabarcea, PhD thesis summary, Institute of Biology of the Romanian Academy (the July 2017 episode, East Constanța profile). Shoreline, lagoons and Danube arms: © OpenStreetMap contributors (ODbL); borders: Natural Earth.
On the same coast
The widened beaches of the Romanian coast — where sand was added and how much stayed. The Romanian seaside, resort by resort — prices, access and beaches. The turquoise sea — why the sea changes colour. Tropical nights — the nights that no longer cool, town by town.