What’s the difference between a hurricane watch and a hurricane warning? What separates a tropical depression from a tropical storm? During a hurricane season, understanding the ins and out of basic weather jargon could help you stay safe.
El Nino
The non-cyclical warming of East Pacific Ocean temperatures off the western coast of South America (extending into the central Pacific) that can result in significant changes in weather patterns in the United States and globally. Years with a strong El Nino tend to be linked to a below-average number of tropical storms and hurricanes across the Atlantic Basin.
Extratropical
A term used in advisories and tropical summaries to indicate that a cyclone has lost its “tropical” characteristics. It is important to note that cyclones can become extratropical and still retain winds of hurricane or tropical storm strength.
Eye
The center of a hurricane (and occasionally a strong tropical storm), characterized by a roughly circular area of light winds, no rain, and sometimes cloud-free skies. An eye will usually develop when the maximum sustained wind speeds exceed about 75 mph. The eye can range in size from as small as
4 miles up to 60 miles or more, but the average size is about
20 miles.
Eyewall
An organized band of deep showers and, at times, thunderstorms surrounding the eye, or center, of a tropical cyclone. Intense rainfall and typically the strongest winds are found within the eyewall.
Hurricane
The name for a tropical cyclone with sustained winds of 74 mph or greater in the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico, eastern and central North Pacific Ocean. Hurricanes are known as “typhoons” in the western Pacific and “tropical cyclones” in the remainder of the world.
Hurricane Season
The time of year when tropical cyclone formation is most likely. In the Atlantic, Caribbean, and Gulf of Mexico, hurricane season runs from June 1 to November 30. The Eastern Pacific hurricane season runs from May 15 to November 30. The Central Pacific hurricane season runs from June 1 to November 30. Hurricanes can — and do — form before and after the “official hurricane season.” Typhoons occur in every month of the year — more frequently than in the Atlantic basin — but are most common in summer and fall.
Hurricane Warning
Hurricane conditions are expected in a specified coastal area within 24 hours.
Hurricane Watch
Hurricane conditions are possible in a specified coastal area within 36 hours.
Landfall
The place that the center of circulation — the center of the eye, if there is one — crosses land. It’s important to note that impacts like rain, wind and surge can precede landfall and can extend far away from the precise point of landfall.
Rain Band
An elongated area of showers and/or thunderstorms often in the form of spiral bands extending away from the core of a tropical cyclone. The bands can span less than 50 miles to hundreds of miles and often persist for more than 12 hours. Rain band widths are usually less than 75 miles wide and, at times, can be less than 20 miles wide. Many individual cloud elements comprise a rain band; sometimes hundreds of individual clouds are associated with a single very long rain band. These individual raining clouds can sequentially move over roughly the same area resulting in severe flooding. Interestingly, some tropical cyclones have well-defined or even extreme rain bands while others appear to have very few rain bands associated with them.
Saffir-Simpson Scale
Developed in the early 1970s by Herbert Saffir, a consulting engineer, and Robert Simpson, then Director of the National Hurricane Center, it is a measure of hurricane intensity on a scale of 1 to 5. The scale categorizes potential wind damage.
Wind Shear
A change in wind speed and/or wind direction vertically or horizontally. Directional (speed) shear is a change in wind direction (wind speed).
Surge
The increase in sea water height (above the level that would normally occur if there was no storm/hurricane) due to onshore winds. Although the most dramatic surges are associated with hurricanes, weaker low pressure systems can cause surge. Surge is estimated by subtracting the normal astronomic tide from the observed tide.
Tropical Cyclone
A warm-core low pressure system which develops over tropical, and sometimes subtropical, waters, and has an organized circulation. Depending on its sustained surface winds, the system is classified as a tropical disturbance, a tropical depression, a tropical storm, or a hurricane or typhoon.
Tropical Depression
A tropical cyclone in which the maximum sustained surface winds are 38 mph or less. It may form slowly from a tropical disturbance oar from a tropical wave.
Tropical Disturbance
An area of organized convection, originating in the tropics and occasionally the subtropics, that maintains its identity for 24 hours or more. It is often the first developmental stage of any subsequent tropical depression, tropical storm or hurricane.
Tropical Storm
A tropical cyclone in which the maximum sustained surface winds are 39 mph to 73 mph. Upon gaining tropical storm intensity, the system is given a name to identify and track it.
Tropical Storm Warning
Tropical storm conditions are expected in a specified coastal area within 24 hours.
Tropical Storm Watch
Tropical storm conditions are possible in a specified coastal area generally within 36 hours.
Tropical Wave
A name for an easterly wave or other generally westward moving disturbance; it has an area of relatively low pressure most typically embedded in the trade wind easterlies. Generally, it is associated with cloudiness, showers, and windy weather. It can be a precursor to tropical cyclone development.
Typhoon
The name for a tropical cyclone with sustained winds of 74 mph or greater in the western North Pacific Ocean. This same
tropical “cyclone” is known as a “hurricane” in the eastern North Pacific and North Atlantic Ocean, and as a “cyclone” in the Indian Ocean.
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