MIAMI (CBSMiami) — When tropical weather starts to threaten, weather forecasts are filled with new terms and ideas that can be confusing especially to people new to South Florida and tropical weather. These terms should help de-mystify hurricane season, and help you to feel a bit more confident as we face the season of storms.
An inverted trough (an elongated area of relatively low pressure) or cyclonic curvature maximum moving east to west across the tropics. These can lead to the formation of a tropical cyclone. Also known as an easterly wave.
A tropical weather system with organized convection (generally 100-300 miles in diameter) originating in the tropics or subtropics, having a non-frontal migratory character and maintaining its identity for 24 hours or longer. It may or may not be associated with a detectable perturbation of the wind field.
A tropical cyclone in which the maximum sustained surface wind speed is 38 MPH (33 knots) or less. Sustained winds are defined as one-minute average wind measured at about 33 ft (10 meters) above the surface.
A tropical cyclone in which the maximum sustained surface wind speed is between 39 -73 MPH (34-63 knots).
An intense tropical cyclone with maximum sustained surface wind speeds of 74 MPH (64 knots) or higher. The term hurricane is used for Northern Hemisphere tropical cyclones east of the International Dateline to the Greenwich Meridian. The term typhoon is used for Pacific tropical cyclones north of the Equator west of the International Dateline.
An organized band of cumulonimbus clouds immediately surrounding the center of the tropical cyclone.
The intersection of the surface center of a tropical cyclone with a coastline. Because the strongest winds in a tropical cyclone are not located precisely at the center, it is possible for a cyclone’s strongest winds to be experienced over land even if landfall does not occur. Similarly, it is possible for a tropical cyclone to make landfall and have its strongest winds remain over the water.
A low pressure system (not associated with a front) that develops over tropical and sometimes sub-tropical waters and has organized deep convection with a closed wind circulation about a well-defined center.
A cyclone (of any intensity) for which the primary energy source is baroclinic (i.e., results from the temperature contrast between warm & cold air masses).
A cyclone that no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. Post-tropical cyclones can continue to carry heavy rains and high winds. Note: former tropical cyclones that become extratropical and remnant lows are 2 specific classes of post-tropical cyclones.
A class of post-tropical cyclone that no longer possesses the convective organization required of a tropical cyclone and has maximum sustained winds of less than 34 knots.
An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide.
The actual level of sea water resulting from the astronomic tide combined with the storm surge.
Tropical Storm Watch
An announcement that sustained winds of 39 to 73 mph are possible within the specified area within 48 hours in association with a tropical, subtropical, or post-tropical cyclone.
Tropical Storm Warning
An announcement that sustained winds of 39 to 73 mph are expected somewhere within the specified area within 36 hours in association with a tropical, subtropical, or post-tropical cyclone.
An announcement that sustained winds of 74 mph or higher are possible within the specified area in association with a tropical, subtropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical storm force winds.
An announcement that sustained winds of 74 mph or higher are expected somewhere within the specified area in association with a tropical, subtropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds. The warning can remain in effect when dangerously high water or a combination of dangerously high water and waves continue, even though winds may be less than hurricane force.
Short Term Watches and Warnings
These warnings provide detailed information about specific hurricane threats, such as flash floods and tornadoes.