A basin-scale pattern of climate variation similar to ENSO though on a timescale of decades (20-to-30 years) and not seasons. It primarily affects weather patterns and sea surface temperatures in the Pacific Northwest, Alaska, and northern Pacific Islands. Causes for the PDO have not yet been explained.

defining the variables for a model.

The time between two successive crests or troughs of a wave. Source: Canadian Hurricane Centre

A former tropical cyclone. This generic term describes a cyclone that no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. Post-tropical cyclones can continue carrying heavy rains and high winds. Note that former tropical cyclones that have become fully extratropical...as well as remnant lows...are two classes of post-tropical cyclones. Source: NOAA-NHC.

The process where water vapor condenses in the atmosphere to form water droplets that fall to the Earth as rain, sleet, snow, hail, etc.

Now known as the Tropical Cyclone Report. A report summarizing the life history and effects of an Atlantic or eastern Pacific tropical cyclone. It contains a summary of the cyclone life cycle and pertinent meteorological data, including the post-analysis best track (six-hourly positions and intensities) and other meteorological statistics. It also contains a description of damage and casualties the system produced, as well as information on forecasts and warnings associated with the cyclone. NHC writes a report on every tropical cyclone in its area of responsibility. Source: NOAA-NHC.

(symbol: p or sometimes P) The force per unit area applied to an object in a direction perpendicular to the surface. Atmospheric pressure is sometimes defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the atmosphere of the Earth. In most circumstances atmospheric pressure is closely approximated by hydrostatic pressure (the pressure at any given point of a non-moving [static] fluid) caused by the weight of air above the measurement point. Low-pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more atmospheric mass above their location. The standard atmosphere (symbol: atm) is a unit of pressure and is defined as being equal to 101.325 kPa. These other units are equivalent: 760 mmHg (torr), 29.92 inHg, 14.696 PSI, 1013.25 millibars.

Force acting on air that causes it to move from areas of higher pressure to areas of lower pressure. Source: NOAA-NWS ERH

The movement of an atmospheric phenomenon. This term is frequently applied to the motion of thunderstorms (or in this case hurricanes) into regions favorable for their continued development.

A vertical density gradient (as determined by the vertical temperature and salinity gradients and equation of state) in some layer of a body of water, which is appreciably greater than the gradients above and below it; also a layer in which such a gradient occurs. The principal pycnoclines in the ocean are either seasonal, due to heating of the surface water in summer or freshwater inputs, or permanent. Source: (c) 1999, American Meteorological Society. Used with permission.