During the summer months, it is common for temperatures to reach over 90 °F (32 °C), with an average of 106.5 days per year, including a majority from June to September, with a high of 90 °F or above and 4.6 days at or over 100 °F (38 °C). However, humidity usually yields a higher heat index. Summer mornings average over 90 percent relative humidity. Winds are often light in the summer and offer little relief, except in the far southeastern outskirts near the Gulf coast and Galveston. To cope with the strong humidity and heat, people use air conditioning in nearly every vehicle and building. In 1980, Houston was described as the "most air-conditioned place on earth". Officially, the hottest temperature ever recorded in Houston is 109 °F (43 °C), which was reached both on September 4, 2000 and August 28, 2011.

How many days per year are Houston temperatures over 90 degrees?