Thomassin is a neighborhood on the mountainside south of Pétion-Ville, Haiti. Many upper-class citizens reside in the area. Climate is tropical with some variation depending on altitude. The average high temperature in Thomassin is 20.3 °C. August being the warmest month with an average of 21.9 °C. January has the lowest temperature of any month through…Thomassin is a neighborhood on the mountainside south of Pétion-Ville, Haiti. Many upper-class citizens reside in the area. Climate is tropical with some variation depending on altitude. The average high temperature in Thomassin is 20.3 °C. August being the warmest month with an average of 21.9 °C. January has the lowest temperature of any month throughout the year, with an average low of 71.3 °C.