Both the archipelagos of the Azores and Madeira have a subtropical climate, although variations between islands exist, making weather predictions very difficult (owing to rough topography). The Madeira and Azorean archipelagos have a narrower temperature range, with annual average temperatures exceeding 20 °C (68 °F) along the coast (according to the Portuguese Meteorological Institute). Some islands in Azores do have drier months in the summer. Consequently, the island of the Azores have been identified as having a Mediterranean climate (both Csa and Csb types), while some islands (such as Flores or Corvo) are classified as Maritime Temperate (Cfb) and Humid subtropical (Cfa), respectively, according to Köppen-Geiger classification.