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The 'humid subtropical climate' (Köppen Cfa) is a climate zone characterized by hot, humid summers and chilly to mild winters. This climate type covers a broad category of climates, and the term "subtropical" may be a misnomer for the winter climate in the cooler areas within this category. Significant amounts of precipitation occur in all seasons in most areas. Winter rainfall —- and sometimes snowfall —- is associated with large storms that the westerlies steer from west to east. Most summer rainfall occurs during thunderstorms and an occasional tropical storm or hurricane.
Humid subtropical climates lie on the southeast side of all continents except Antarctica, roughly between 24 and 40 degrees. The only exception where this climate zone reaches up to latitude 44° North, is the Po Valley and the Toulouse region, in Europe. The main temperature range in this climate, considering normal annual extremes, is 10 to 110 °F (-12 to 43 °C), though this range may vary greatly depending on the exact location.

Contents

Africa

Asia

Isolated humid zones in western Asia

Australia

Variations in Australia

Europe

North America

Characteristics and variants

South America

Africa

In Africa, this climate type is found only on the east coast of South Africa including Durban and extends northward into extreme southern Mozambique.

Asia

Humid subtropical climates in Asia differ from those in other continents in generally having a very pronounced dry winter even on the poleward boundary of this region. They occupy extensive arcs of relatively low land from northern Pakistan circling the Himalayas to China, South Korea and Japan north to Tokyo and Niigata. However, the distinction is difficult to make in Japan, whose temperatures can either be considered subtropical or humid continental, especially in the south and depending on elevation. Some major Asian cities in this climate zone include Islamabad, Kathmandu, Chongqing, Chengdu, Shanghai, Nanjing, Busan, Kyoto and Tokyo ''(the latter on the very northern fringe)''. Hong Kong and Taipei are on the equatorward boundary of this zone.
In most of this region, there is very little precipiation during the winter owing to the powerful anticyclonic winds from Siberia. Only in those parts of coast eastern China between about the Yellow River and the Pearl River is there sufficient winter rainfall to produce a 'Cfa' climate and even in these areas rainfall and streamflow show a very pronounced summer peak quite unlike other regions of this climate type. The ''only'' area where the winter rainfall equals the summer rain is on the "San-in" (Sea of Japan) coast of Japan, which during winter is effectively on the windward side of the westerlies. The winter rainfall in these regions is usually produced by low pressure systems off the east coast that develop in the onshore flow from the Siberian High. Summer rainfall comes from the East Asian Monsoon and from frequent typhoons.
Annual rainfall, except in the northernmost regions around Tianjin and Shandong, is generally over 1,000 mm (40 inches), and in areas below the Himalayas can be much higher still. In the west humid subtropical climate border on continental climates as altitude increases, or on winter-rainfall climates in Pakistan.

Isolated humid zones in western Asia

Although humid climates in Asia are mostly confined to the southeastern quarter of the continent, there are some isolated areas on the Black and Caspian Seas than possess humid climates that are unusually warm for their high latitudes.
In the narrow Caspian coastal strip of Iran (Gilan and Mazandaran) a humid subtropical climate prevails at an unusually high latitude. Annual rainfall ranges from around 740 mm (29 inches) at Sari to over 2,000 mm (78 inches) at Astara, and is heavy throughout the year, with a maximum in October or November when Astara can average 400 millimetres (16 inches). Tempteratures are generally moderate in comparison with other parts of western Asia. In Rasht, the average maximum in July is around 28 °C (82 °F) but with near-saturation humidity, whilst in January it is around 9 °C (48 °F).
In Georgia and the adjacent region of Turkey, the Kolkheti Lowland has a climate similar to that of Gilan in Iran. Temperatures range from 22 °C in summer to 5 °C in winter and rainfall is even heavier than in Caspian Iran—up to 2,300 millimetres per year in Hopa—and it falls throughout the year. This climate is almost a 'Cfa'/'Cfb' borderline case, however.

Australia

The humid subtropical climate dominates most of eastern Australia south from about Bundaberg, Queensland down to about Bega on the south coast of New South Wales. It extends from the coast inland to about Dubbo and the Warrumbungle and Nandewar mountain ranges, where it grades into arid climates. In the Great Dividing Range and to the south of about Bega, this climate type grades into warm temperate climates (Köppen 'Cfb') as at Guyra and Katoomba, in New South Wales.
This zone contains the only regions where soils are not acutely deficient in phosphorus, as well as the heaviest rainfall south of the Tropic of Capricorn, making it prime agricultural country, centred on towns such as Coffs Harbour, Grafton, Port Macquarie, Tamworth, and Moree.
Many of Australia's major cities are also in this climate zone, including Sydney, Brisbane, Gold Coast-Tweed Heads, Newcastle and Wollongong.

Variations in Australia

There is considerable variation in climate within this zone. Annual rainfall on the coast can reach as high as 2,000 mm (80 inches) in favourable locations and is generally above 1,000 mm (40 inches). However, because most of the heaviest two- and three-day rainfalls in the world occur in this coastal zone as a result of east coast cyclones forming to the north of a large high pressure system, there can be great variation in rainfall from year to year. At Lismore in the centre of this zone, the annual rainfall can range from less than 550 mm (22 inches) in 1915 to more than 2,780 mm (110 inches) in 1950. There is usually a distinct summer rainfall maximum that becomes more pronounced moving northwards: in Brisbane the wettest month (February) receives five times the rainfall of the driest (September).
Temperatures in this zone are typically very warm but not excessive: the average maximum in January is usually around 28 °C (82 °F) and in July around 19 °C (66 °F). Frosts are extremely rare except at higher elevations.
In the Darling Downs and further south, the summer rainfall maximum is less marked and by the time one reaches Dubbo, there are actually on average more rainy days in the winter months. Temperatures here are more extreme, with summers being generally very hot with maxima of around 32 °C (88 °F) and frosts being common during dry winters: at Mitchell the temperature has reached as low as -9.4 °C (15 °F).
North of the 'Cfa' climate zone there is a zone centred upon Rockhampton and extending up to the Atherton Tableland of Köppen 'Cwa' climate. This has a very pronounced dry winter with often negligible rainfall between June and October, and winter temperatures generally only slightly below the limit required for tropical climates.

Europe

The 'Cfa climate' can be found in an area going from the Po River valley in Northern Italy and southeast through coastal or near-coastal portions of Slovenia and Croatia. Summer rainfall is here considerably greater than in the mediterranean climates found around the Mediterranean Sea, and winter temperatures hover just above freezing.

North America

In North America, humid subtropical climates are almost exclusively the domain of the American South, including part or most of eastern Texas, Louisiana, most of Arkansas, Mississippi, Tennessee, Kentucky, Alabama, North Carolina, South Carolina, Georgia, most of Florida and Virginia, except for upland regions including Southwest Virginia. It also exists in low lying or urban areas, in some cases extending just south of 40N in Delaware, extreme southwestern and the eastern panhandle areas of West Virginia, eastern and central Maryland, southeastern Pennsylvania (Philadelphia metropolitan area), southern New Jersey, and extreme southern Ohio.
Major cities in this climate zone include Houston, San Antonio, Austin, Dallas, Atlanta, Memphis, New Orleans, Birmingham, Nashville, Chattanooga, Greenville (SC), Charlotte, Raleigh, Jackson (MS),Jacksonville, Orlando, Tampa, Richmond, and Little Rock. Cities on the northern periphery of this zone include Tulsa, Louisville, Cincinnati, Washington (DC), Baltimore, Philadelphia (northernmost metropolitan area), Wilmington (DE), and Atlantic City. Dallas and Oklahoma City show marked reduction in rainfall that suggests a shading into steppe climates to be found farther west, as in Lubbock, Texas. Some of these cities, such as Tampa, New Orleans and Atlanta, are of a warmer variety; and others, such as Washington, Cincinnati and Louisville, are of a colder variety.

Characteristics and variants

The southernmost limits of this climate are around Miami and southern coastal Texas, and areas further south have a true tropical climate with a very warm weather year round and minimal temperature differences between seasons. The northernmost limits of the humid subtropical climate are around Philadelphia and adjacent southern New Jersey or around 40°N, southwest to Washington, D.C. and the edge of the Blue Ridge west to Louisville, Kentucky then roughly along the Ohio River through Paducah, Kentucky to south of Springfield, Missouri. Areas further north, inland, or higher in elevation which have a humid continental climate with colder winters.
Snowfall varies greatly in this climate zone. In areas around Florida and the Gulf Coast, snowfall is very rare and it occurs a few times per generation. In southern cities farther north, such as Atlanta, Little Rock, Nashville, Dallas, Greenville, Charlotte, Raleigh, and Norfolk, snowfall is sporadic, but occasional light snow and ice storms are not unusual. Into the northern limits of this climate zone, in cities like Baltimore, Cincinnati, Philadelphia, and Louisville, snow is more common and it occurs every year, sometimes accumulating heavily.
Precipitation is plentiful in the humid subtropical climate zone. Although most areas tend to have precipitation spread evenly throughout the year, a somewhat monsoon-like pattern is seen in parts of the Southeast (in locales such as Augusta, Georgia and Columbia, South Carolina), which experience an extremely dry (by humid subtropical standards) and warm spring, followed immediately by a long, hot, rainy and humid summer. In addition, areas in Texas that are slightly inland from the Gulf of Mexico, such as Austin, generally see a peak of precipitation in the spring, and a deep, drought-like nadir in mid-summer.

South America

In South America, this climate type exists primarily in the Pampas of Argentina and Paraguay, Uruguay and southern Brazil (the states of São Paulo, Paraná, Santa Catarina and Rio Grande do Sul).
The 'Cwa' climate type with a distinctly dry winter is found to the west of this zone in Northwestern Argentina, extending south to the Sierra de Córdoba, where it grades into arid and semi-arid climates. In the Sierras and the Andes to the west, it grade into much colder climates where trees cannot grow.