According to the Koppen climatic classification, the letter code Cfa denotes a humid subtropical climate.

Option 1, tropical wet climate, does not match with the letter code Cfa. Tropical wet climates are denoted by the letter code Af in the Koppen classification. These climates are characterized by high temperatures and abundant rainfall throughout the year.

Option 3, tundra climate, also does not match with the letter code Cfa. Tundra climates are denoted by the letter code ET in the Koppen classification. These climates are characterized by very cold temperatures, low precipitation, and a short growing season.

Option 4, tropical wet and dry climate, is also not the correct choice for Cfa. Tropical wet and dry climates are denoted by the letter code Aw in the Koppen classification. These climates have distinct wet and dry seasons with high temperatures throughout the year.

Therefore, the correct answer is option 2, humid subtropical climate, which matches with the letter code Cfa in the Koppen classification. Humid subtropical climates are typically found in the southeastern parts of continents and are characterized by hot and humid summers, mild winters, and a moderate amount of precipitation throughout the year.