Africa
In the Northern Hemisphere, in August it's the height of summer: in North Africa, south of the Sahara, the monsoon prevails, while in the Red Sea it's too hot. In the Southern Hemisphere it's winter, and even at tropical latitudes it can be a little cool. In Cape Verde, the rainy season begins, though irregular. You can visit the mountain cities that are located around the Equator or a little further to the south.
Where to go: Brazzaville, Dar es Salaam, Gaborone, Harare, Kampala, Kigali, Libreville, Lilongwe, Luanda, Lusaka, Maputo, Mbabane, Nairobi
Asia
In August it's still summer, and it's hot in many areas. The monsoon season continues in much of South-central and Eastern Asia, sparing some parts of Indonesia.
Where to go: Jakarta, Kuala Lumpur, Lhasa, Omsk, Singapore, Ulaanbaatar
North and Central America
August is the second central month of summer, and the climate is similar to that of July. Summer is the best period in the northern areas. It's often too hot in the United States, and sometimes even in Southern Canada, except on the Pacific Coast, which is cooler. In California and Baja California it's sunny, but sometimes the hot Santa Ana wind blows, especially on the southern coast, while in inland areas the heat is scorching. Hot, muggy and rainy weather lingers on in the Gulf of Mexico and Central America, where in addition the hurricane season reaches its climax.
Where to go: Anchorage, Ilulissat, San Francisco, Seattle, Vancouver
South America
In the Southern Hemisphere, in August it's still winter. In the north of the continent, in the Northern Hemisphere, it's summer, so it's hot and rainy. In some areas around the Equator, the dry season begins. In the Andean region, from Ecuador to the south, the dry season continues.
Where to go: Asunción, La Paz, Quito, Rio de Janeiro, Sao Paulo
Europe
August is the warmest month along with July. In Northern Europe, the days are still long, but less than in July, and generally the rains begin to increase a little, and the temperature begins to decrease, especially in the second half of the month. In Southern Europe it's still hot and sunny, while afternoon thunderstorms are still possible in Central Europe.
Where to go: Amsterdam, Berlin, Brussels, Copenhagen, Dublin, Edinburgh, Helsinki, Geneva, Kiev, London, Ljubljana (second half), Luxembourg, Minsk, Moscow, Oslo, Paris, Prague, Reykjavik, Riga, St. Petersburg, Stockholm, Tallinn, Tórshavn, Warsaw, Vilnius
Oceania
It's still winter in the Southern Hemisphere, so it's still the coolest and driest season on the tropical islands. In Northern Australia, the dry season continues, so you can go even though it's hot. In Brisbane and the Gold Coast the weather is still mild.
Where to go: Brisbane, Darwin, Papeete, Port Moresby