Dorian now a Catagory 5 hurricane. Be on alert for watches and warnings that pertain to your area. 

Eyewall (noun, “EYE-wall”)

This is a ring of intense rain and wind that swirls around the calm center of a tropical cyclone. These powerful storms develop over warm ocean waters just north and south of the equator. They have different names in different regions of the world. Tropical cyclones are “hurricanes” when they occur in the western Atlantic and eastern Pacific north of the equator. They’re “typhoons” in the western Pacific, and “cyclones” south of the equator. All tropical cyclones are destructive storms that have spinning bands of wind and rain. At the center, there’s a calm spot called the eye. Surrounding the eye are the strongest storms of the hurricane or cyclone — the eyewall. The eyewall gets its name because the clouds often pile up higher around the eye.  This creates a wall of clouds around the eye when the storm is seen from above.

When ocean waters get warm, they warm the air above them, too. That warm air rises up, leaving an area with low pressure below it. Cooler air rushes in to the space and begins to warm. As the warm air rises, it cools and forms clouds — which produce wind and rain. The clouds grow as more warm air comes up, and the system begins to spin. The spinning creates a calm eye in the middle of the storm. The clouds around the calm eye will have the fastest spin, piling up clouds around the calm center and creating the eyewall.

In a sentence

Scientists use the wind speeds in the eyewall of a tropical cyclone to judge its intensity.

A glimpse inside a super typhoon.

This is an internal profile of super-typhoon Uusagi, which struck Taiwan and the Philippines in 2013 (see http://tinyurl.com/mgdebue). As it approached Taiwan, a satellite borne radar system took this image of a meteorological phenomenon called hot towers in the outer eyewall of the typhoon along with the rain that was belting down in varied parts of the weather system. Hot towers are rapidly rising cumulonimbus anvil clouds that carry the moisture rapidly upwards up to an altitude of 15km. They can rise so high as to punch into the stratosphere depositing ice crystals. They are named after the immense amount of latent heat held by their moisture that is released as they condensate into rain.

The appearance of hot towers indicate a strengthening storm, and reveal the heat engine of rapidly rising moist air driving the typhoon. Shortly after this image was taken, Usagi briefly strengthened to category 5, the highest on the scale Both the eyewall and rainfall pattern are very symmetrical for a cyclone, and indicate an energy efficient system. Such annular eyewalls tend to indicate longer lived cyclones, as they do not dissipate their energy as much as turbulence.

Loz

Image credit: Owen Kelly/ NASA

http://earthobservatory.nasa.gov/blogs/earthmatters/2013/09/23/a-view-inside-super-typhoon-usagi/?src=fb

http://earthobservatory.nasa.gov/blogs/earthmatters/2012/09/12/discovering-hot-towers/