Tropical Wave: A "bump" or disruption of normal tropical easterly flow. Associated turning of wind causes low-level convergence of air, which helps with falling pressure and enhanced showers.
This can evolve into a Tropical Depression, which is a closed circulation of air in the low levels. This in turn increases convergence and pressure falls, and wind speeds increase in a Catch-22 effect (i.e. the stronger the wind blows the greater the convergence, the quicker the pressure falls... so the stronger the wind, etc.).
Once sustained winds reach 39 mph in the closed circulation a Tropical Storm is named. Usually there are at least 2 closed isobars (lines of equal pressure) of 4 mb increments around the center. If atmospheric conditions remain correct the system will evolve into a...
Hurricane. There is usually a difference in pressure of at least 0.60 inches of mercury between the center and surrounding pressure field, with the greatest change near the center (eyewall). It is this great difference in pressure, which sometimes can be as great as 2.95 inches of mercury, that causes the wind to be so strong.
A mature hurricane is a well-oiled meteorological machine, but disruption of the processes that drive the storm (i.e. interaction with land or colder air feeding in) will begin to destroy the storm, and the disintegration of a hurricane can often be quick and dramatic.
Weather plays a bigger role than you may think when it comes to seasonal outdoor allergies.
Why can different types of precipitation be seen on Earth while temperatures remain constant?
Dangerous flash flooding is captured as an arroyo becomes filled with water in Carson Valley, Nevada.
The RealFeel Temperature uses an equation to determine how it actually feels outside.
Knowing what the different advisories, watches, and warnings mean will lead to more informed decision making when a winter storm threatens a particular area.
How can you determine if and when the ice is thick enough for safely going out on?
Seeking shelter in the event of a tornado could save your life, but is there really any safe place to hide?
Driving on a 90-degree angle away from the tornado is a good strategy to follow in order to distance yourself from the tornado.
Supercell thunderstorms have been responsible for major tornadoes that have demolished parts of the U.S.
After a cold, clear winter night without much wind, the ground and nearby tree branches may be covered by tiny, white ice crystals.
Philadelphia, PA (1991)
96 degrees -- a record sixth 90-degree reading for the month. (The month ended with twelve 90-degree days.)
Chicago, IL (1992)
32 degrees, latest 32 or lower on record.
Iowa City, IA (1859)
Waterspout; 8 killed, one child was taken up, carried 500 yards and thrown in a slough but survived.