page_title: Sky
section_title: Tropical cyclones
hierarchical_section_title: Sky / Use in weather forecasting / Tropical cyclones
caption_attribution_description: English: The eyewall of a tropical cyclone, taken from a P-3.
context_page_description: The sky is everything that lies above the surface of the Earth, including the atmosphere and outer space.
  In the field of astronomy, the sky is also called the celestial sphere. This is an abstract sphere, concentric to the Earth, on which the Sun, Moon, planets, and stars appear to be drifting. The celestial sphere is conventionally divided into designated areas called constellations.
  Usually, the term sky informally refers to a perspective from the Earth's surface; however, the meaning and usage can vary. An observer on the surface of the Earth can see a small part of the sky, which resembles a dome appearing flatter during the day than at night. In some cases, such as in discussing the weather, the sky refers to only the lower, denser layers of the atmosphere.
  The daytime sky appears blue because air molecules scatter shorter wavelengths of sunlight more than longer ones. The night sky appears to be a mostly dark surface or region spangled with stars. The Sun and sometimes the Moon are visible in the daytime sky unless obscured by clouds. At night, the Moon, planets, and stars are similarly visible in the sky.
context_section_description: Within 36 hours of the passage of a tropical cyclone's center, the pressure begins to fall and a veil of white cirrus clouds approaches from the cyclone's direction.  Within 24 hours of the closest approach to the center, low clouds begin to move in, also known as the bar of a tropical cyclone, as the barometric pressure begins to fall more rapidly and the winds begin to increase. Within 18 hours of the center's approach, squally weather is common, with sudden increases in wind accompanied by rain showers or thunderstorms. Within six hours of the center's arrival, rain becomes continuous. Within an hour of the center, the rain becomes very heavy and the highest winds within the tropical cyclone are experienced. When the center arrives with a strong tropical cyclone, weather conditions improve and the sun becomes visible as the eye moves overhead. Once the system departs, winds reverse and, along with the rain, suddenly increase. One day after the center's passage, the low overcast is replaced with a higher overcast, and the rain becomes intermittent. By 36 hours after the center's passage, the high overcast breaks and the pressure begins to level off.
caption: Picture of the sky in the eye of a tropical cyclone
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